Intro to Human Biology- Lecture 1-27

Biology: the study of living things- Bacteria, fungi, protists (single-celled organism living on soil), plants, animals

Characteristics of Living Organisms:

1. Organized
2. Utilize energy
3. Reproduction- copies of themselves (ex. Like a computer virus)
4. Growth and development- Develop families (ex. Like AI)
5. Maintain Homeostasis- organism must sense its environment to know that a change occurred (alteration in homeostasis)
6. Respond to stimuli- signals sent all across the body
7. Evolutionary history- differences in traits across time

Human Characteristics - From atoms to organs

1. Atoms - smallest particles of matter
2. Molecules - formed by atoms - make up cells of the body
3. Cells - humans are multicellular - we have many different types of cells, specialized to different roles
4. Tissues - collections of similar cells grouped together (neuro, muscular, connective, epithelial)
5. Organs - collections of similar tissues grouped together to make a functional unit
6. Organ systems - collections of different organs that work together to carry out physiological processes

Utilize Energy

• Processes that sustain life require energy
• Energy taken in from the products we consume
  • Animal products- energy held/stored in the chemical bonds of the animal tissue
  • Plant products- energy taken in from the Sun - the source of all energy for life on Earth
  • Sun → plants → animals → humans
• Food is broken down when consumed, breaking chemical bonds within the food → where energy is stored to be released

Reproduction

• All living organisms pass on their genetic material to their offspring- achieving this through sexual reproduction
  • Combining of genetic material from two distinctly different individuals
  • Results in offspring that are not exact copies of either parents → increased variability in the population
• Individual cells also replicate in humans – result is identical copies of these cells
• Plays into evolution & natural selection in the human population

Growth & Development

Growth: an increase in the size and number of cells; part of the development process

Development: all changed that occur from fertilization of the egg until death

Development is broken into stages:

• Infant
• Child
• Adolescent
• Adult
• Elderly

Maintain Homeostasis

Homeostasis: the maintenance of a stable internal environment within an organism

• Not static!
• Homeostasis is the combination of many processes within the body that allow it to be stable
• EX]
  • Body temperature - 98.6ºF (37ºC) in humans
  • Humans are warm blooded - they maintain a constant temp. - important b/c chemical reactions in the body work at this optimum temperature
  • Body temperature does vary throughout the day - wake/sleep cycles - but within a narrow range;
    • Ever noticed temperature changes based on time of day?
• Maintaining temperature as a homeostatic point
  • Shivering- decreased body temp. & muscles will contract quickly in order to generate heat (byproduct)
  • Goosebumps- decrease body temp.; raise the hair on the body to trap a layer of heat
  • Sweating- increased body temp.; fluid released to surface of the skin; evaporation of fluid cools the skin
• Blood vessels and body temp
  • Vasoconstriction- pulls blood away from the surface of the body; decreased access of blood to the colder environment → heats the core of the body
  • Vasodilation- opens the blood vessels in extremities in order for blood to be at surface of the skin; heat released from blood through skin → cools the body → allows for components of sweat to exit the blood

Respond to Stimuli - necessary for homeostasis to be maintained

• Mechanisms for things like increasing body temperature and regulating blood pressure
• Cells within the body communicate with the brain and cause changes to occur within the body to return to set point
• EX.] Baroreceptors (pressure receptors) within the body detect changes in blood pressure and allow for the blood pressure to be changed as necessary
  • Stand up quickly, BP drops
  • Baroreceptors increase the BP in order to drive blood to the brain against gravity

Evolutionary History

• Living organisms evolve - undergo change over time
• Adaptation: changes in the genetic makeup of a population in response to a change in environment
• Ex.] Sickle cell trait in Africa
  • Protective against malaria
  • Seen more frequently as these genes are passed on while others do not survive to reproduce

** These characteristics of life are NOT exclusive to humans

• All living organisms in some way share these traits: Unicellular & Multicellular, plants & animals, bacteria & fungi
• Mammals (Animal Kingdom) share other traits:

1. Backbones (vertebrates)
2. Lungs (and diaphragms)
3. Warm blooded (homeotherm / endotherm)
4. Birth of live young
5. Milk for young
6. Hair
7. 4 Chambered heart

Uniqueness of Humans

• Intelligence: larger cerebrum that allows for higher thoughts, language, reasoning
• Posture: walk on two legs, hands free of weight support
• Skin: able to lose heat to the environment in order to cool the body – we can be active for longer periods
• Opposable Thumbs: able to use hands with more efficiency
• Throat: able to speak and communicate due to structure of human throat
• Slower maturation: young more dependent for longer period

Intelligence

• Cerebrum is the center of higher thoughts - we seek knowledge, unlike other mammals
• How do we gain knowledge:
  • Culture – how we are raised, traditions of family
  • Authority – what we are told
  • Experience – touch the hot stove…
  • Reasoning
    • Deductive: applying general rule to specific cases (ex. Generally this is true about this population, so it must be true about this specific individual)
    • Inductive: learn from a specific case and apply as general rule
  • Scientific discovery – experiment!

Scientific Method- Lecture 2: 1-27-25

Science: the body of knowledge derived from observation & experimentation

Scientific Method: technique used with specific steps in order to take a question formed from an observation and draw conclusions; utilized hypotheses, variables, & controls

Steps

1. Observe & Question: drawn from the natural environment. A question is formed based on what is seen
2. Formulate a Hypothesis: A tentative explanation of what you have observed, including what you predict is happening
3. Experimentation and Data Collection: An experiment is used to test the hypothesis & data is taken from the experiment
4. Reject or accept hypothesis: Did the experiment support what you thought was occurring in the observation?
5. Draw Conclusions: State for others what you have found and how it applies; This often involves peer review in order to remove experimenter bias

Variables

• Independent variable: Variable that will be manipulated during the experiment
• Dependent Variable: Variable that will be changed due to the manipulation of the independent variable (what you measure)
• Control: The group in the experiment that does not undergo any manipulation. This is for baseline comparisons
• Standardized Variable: the variable that is kept consistent for the experimental groups and the control group

Theory vs Hypothesis

• Theory: generally accepted statements in science that aren’t testable by a single hypothesis. These have not yet been disproved but could be.
  • Germ Theory: Disease is caused by medical microorganisms (pathogen)
    • S. aureus skin infections
    • Rhinovirus and the common cold
  • Hypothesis: part of the scientific method that states an observation about a specific case. Not widely accepted and not supported by multiple experiments

Rejection of a theory-

Theory of Spontaneous Generation: stated that living things arose spontaneously from nonliving matter (Aristotle)

Critical Thinking

• The process that allows us to objectively analyze facts, issues, problems and information
• Distinguish between beliefs and knowledge to support the idea
• You have to believe in the scientific method; 7 general rules

1. Gather complete info, not just from sources that support your viewpoint
2. Understand and define all terms
3. Question the methods by which data and information were derived
   1. Were the facts derived from experiments?
   2. Were the experiments well executed? Have they been repeated?
   3. Did the experiment include a control group and an experimental group?
4. Question the conclusions?
   1. Are the conclusions appropriate?
   2. Was there enough info on which to base the conclusions?
5. Uncover assumptions and biases
   1. Was the experimental design biased?
   2. Are the underlying assumptions that affect the conclusions?
6. Question the source of the information
   1. Is the source credible?
   2. Is the source an expert or supposed expert?
7. Understand your own biases and values

Chemistry and the Body

• All organisms are made up of different combinations of chemicals
• Chemical reactions within the body allow for life to exist
  • All chemical reactions within the body occur in an aqueous environment
• Water (a chemical!) makes up nearly ⅔ of our body
• Hydrogen bonding, seen in water, is also observed in other places in the body

Atoms

• The smallest unit of matter we will consider for this course
  • Matter = anything that takes up space
• Atoms are made of subatomic particles

1. Protons- positively charged, found in the nucleus of the atom
2. Neutrons- neutral charge, found in the nucleus
3. Electrons- negatively charged, found in the space around the nucleus

Elements

• Pure substances that are the basis for all of compounds found on earth
• 92 naturally occurring
• 20 found in organisms
  • Carbon, Nitrogen, Oxygen and Hydrogen make up 98% of atoms in living organisms
• Atomic number = number of protons in the atom
  • This number NEVER changes

Chemical Bonds

• All atoms want to have 8 total electrons around their shell
  • Exception: hydrogen only has 2 valence electrons
• Atoms join together by
  • Ionic bonds- bonds formed when one atom gains an electron and one atom loses and electron (NaCl – table salt)
  • Covalent bonds- bonds formed when electrons are shared between two atoms
    • Nonpolar covalent- equal sharing of electrons (methane- CH4)
    • Polar covalent- unequal sharing of electrons (water- H2O)

Polar Covalent Bonds

• Unequal sharing of electrons due to one atom attracting electrons more strongly than the other atom
• Partial negative and positive charges are created within the molecule

Electronegativity

• Nonpolar covalent → polar covalent → Ionic (Least to most electronegativity; determines strength of bond)
• Hydrogen (valence =+1; electroneg. = 2.20), Carbon (valence =+4, -4; electroneg. = 2.55), Oxygen (valence =-2; electroneg. = 3.44)

Hydrogen Bonds

• These are intermolecular bonds - occur between the atoms of different molecules
• This is what holds water together; also seen in DNA; gives water important characteristics that are vital to life!!

Intramolecular (Intra- Within)

• Bonds within a single molecules
  • Ionic
  • Polar covalent bonds
  • Nonpolar Covalent
• NOT easily broken- requires a chemical reaction

Intermolecular (In between)

• Hydrogen bonds
  • In between 2 molecules
• Easily broken and reformed (unless frozen)

Why is water vital to life?

• Liquid at room temperature; drink it, cook with it, bathe in it, wash objects w it
• Its temperature changes slowly, prevents sudden changes in environment of chemical reactions
• Maintains new temperature – acts as a temperature buffer
  • Takes twice as much energy to change the temp. of water when compared to other covalently bonded liquids
• High heat of vaporization - prevents body from overheating
  • Evaporations of sweat removes heat generated by the body
• Water is most dense at 4 degrees C, not at freezing. Rather than contracting when it freezes, water expands
• Cohesive due to hydrogen bonds joining water molecules; important in blood moving in the body
• Solvent for polar and charged molecule – facilitates chemical reactions inside and outside of the body

Acids and Bases

• Acids- substances that release hydrogen ions
  • Causes a higher concentration of H+ than OH- (written [H+] > [OH-])
• Bases - substances that accept hydrogen ions or release hydroxide ion
  • Causes there to be a higher concentration of OH- than H+ (written [H+ < [OH-])
• Neutral solutions have equal amounts on both ions

Strong vs. Weak

• Strong acids: Complete dissociation (“ionization”) in solutions
• Weak acids: Partial dissociation; some hydrogen will remain bound
• Strong bases: Complete dissociation; releases hydroxide ion
• Weak bases: Partial dissociation

Buffers in the Body

• Buffer systems are:
  • A way to regulate pH change
  • Weak acids and bases that resist pH changes
• Ex. H2O + CO2 ←→ H2CO3 ←→ H+ + HCO3-
• This reaction goes both directions. If an acid is added to this, H+ will be in abundance, shifting the reaction to the left to increase the pH by forming more H2CO3. If the H+ is removed from the solution, the reaction shifts to the right to form more hydrogen ion and decrease the pH

Organic and Inorganic Molecules

• Inorganic Molecules - Not made primarily of carbon
  • Generally small
  • Usually contain ionic bonds
  • Sodium chloride; dissociate well in water
• Organic compounds/molecules - contain molecules that are made primarily of carbon (able to form 4 covalent bonds); ex. Methane
  • Proteins, carbohydrates, nucleic acids, lipids
  • Usually large
  • Covalently bonded; nonpolar or polar
  • Exception – carbon dioxide is inorganic
• Carbohydrates (carbons that are fully hydrated)
  • “Sugar”; made of carbon, hydrogen and oxygen
  • 1% of body weight in human body, carbs are essential to life
  • Starches, vegetables, fruits, and added sugars
• Simple sugars
  • Monosaccharides - monomers - smallest subunit (simplest form of carbs)
    • Example: C6H12O6 (Glucose)
  • Disaccharides - formed by the joining of two monosaccharides by a dehydration reaction
    • Glucose + Fructose = sucrose (honey, maple syrup)
    • Glucose + Galactose = lactose
    • Glucose + Glucose = maltose (beer)
  • Oligosaccharides - between simple sugars and polysaccharides (3-100 monomers)
    • Join with proteins to make glycoproteins (cell markers)
• Complex carb/sugar: Polysaccharides
  • Hundreds of monomers joined together
  • Can be structural or storage polysaccharides; not easily broken down
  • Plants
    • Fiber- forms the cell wall, not digestible by humans; Binds to water and some cholesterol. Works to soften and add bulk to stool
    • Starch- the storage form in plants; Found in the cytoplasm of the cells
      • Corn, potatoes, grains, peas, and beans contain starch in high amounts
      • Largest source of carbohydrates in the American diet (sugars are closer)
  • Animals
    • Glycogen - storage form in humans, mostly found in the liver and muscle
      • Muscle - broken down to provide energy in the muscle tissue (bc it can´t pass through the cell membrane in it´s OG size)
      • Liver - broken down if blood sugar drops in order to provide sugar for cells
    • Chitin - structural - seen in the exoskeleton of insects
• Lipids (ex. Oil, avocado)
  • Nonpolar - will not dissolve in water
  • Made of carbon, hydrogen and oxygen
    • Phosphate as well in some cases
  • 15% of body mass
• 4 categories of Lipids
  • Triglycerides
    • Three long hydrocarbon chains; the chains are called fatty acids
    • Bond to glycerol (the backbone of the molecule)
    • All fatty acids have a carboxyl group at the top; this is a carbon double bonded to one oxygen and single bonded to a second oxygen
  • Saturated Fatty Acid
    • No carbon/carbon double bonds found in the fatty acid chains
      • “Saturated” - all carbon molecules are bound to the maximum amount of hydrogen atoms possible
    • Chains are straight and are able to stack - makes these solids at room temperature
    • Ex. Butter, bacon
  • Unsaturated Fatty Acids
    • Contain at least one carbon/carbon double bond
      • More than one of these double bonds - polyunsaturated
      • “Unsaturated” - carbon atoms do not have maximum amount of hydrogen bound
    • Not able to stack due to double bond - liquid at room temperature (Ex. veg oil)
  • Trans Fats
    • Manipulated hydrogens around the double bond to make these stackable
    • Makes unsaturated fatty acids into a form that is a solid at room temperature
    • Not recognized by the body; associated with increased risk of heart disease and high cholesterol (Ex. Margarine, donut)
• Phospholipids
  • One of the main components of the cell membrane
  • Glycerol is bound to 2 fatty acids and 1 phosphate group
  • Hydrophilic (water loving) head- polar, hydrophobic (water fearing) tail- nonpolar
    • Lipid bilayer
• Steroids
  • 4 interconnected carbon rings
  • Whatever is attached to the 4 ring structure determines the molecule
  • Examples: cholesterol, glucocorticoids, sex hormones
• Waxes
  • Forms of fatty acid chains with alcohols
  • Feathers of birds, fur of some animals
    • Water repellent
  • Found on leaves and plant surfaces
• Proteins
  • 17% of the mass of the human body is made up of protein
  • Carbon, hydrogen, oxygen and NITROGEN (primary difference between lipids)
    • Some have sulfur as well
  • Monomers (most basic form) = amino acids - joined by peptide bonds
  • Polypeptides = 50 Amino Acids (or less)
  • Proteins = more than 50 Amino acids
• Protein Structure- type of amino acid and where it is in position that forms the structure
  • Primary structure: the amino acid sequence within the polypeptide
  • Secondary structure: results from hydrogen bonds forming between different portions of the long chain
  • Tertiary structure (interactions with water): Overall structure is created by different R groups interacting with water in the cells. Hydrophobic R groups move to the center of the structure and hydrophilic (polar or ionic- charge) to the outside
  • Quaternary structure: Created from interactions between multiple polypeptide subunits of one protein- multiple chains and how they interact. Many proteins consist of many subunits of polypeptides (ex. Hemoglobin has 4 polypeptide subunits)

Functions of Proteins

1. Support - keratin - hair, nails, tendons, ligaments, skin
2. Enzymes - catalyze chemical reactions (enzymes are a type of protein)- decrease the activation energy of a reaction
3. Transport - channels and carriers in cells
4. Defense - antibodies of the immune system
5. Hormone - (interpreted as a message) regulation of body function
6. Motion and force- actin and myosin in muscle
7. Energy - last resort (carbon bonds → energy stored in protein, typically not used)

** Enzymes

Nucleic Acids

• DNA and RNA
• 3 subunits - Elements included = phosphate, nitrogen, carbon, hydrogen and oxygen
  • Phosphate group
  • Pentose sugar (deoxyribose [ex. cytosine] or ribose)
  • Nitrogen containing base (adenine, thymine, guanine, cytosine, uracil)

Unit 3: Cell Structure Overview - 2/5

Microscopes: Illuminating Structure of Cells

• Microscopes fall into two broad categories
  • Light microscopes
    • Use ordinary visible light to illuminate the specimen
    • Can magnify objects 100-400x their original size
  • Electron microscopes
    • Use a beam of electrons to create a visual image of the specimen
    • Can enlarge objects 100,000x their original size

Cell structure

• The cell consists of two main compartments:
  • The nuclear (nucleus) compartment
    • Contains genetic info
    • Regulates the structure and function of the cell
  • The cytoplasmic compartment
    • Space b/w the nucleus and the plasma membrane
    • Contains numerous cellular organelles, which perform specific functions
• Eukaryotic - identifiable nucleus
• Prokaryotic- plant/bacteria

The Nuclear and Cytoplasmic Compartments

• Cytoplasmic compartment is home to the cytoskeleton- network of tubules and filaments
• Binds to enzymes, putting them in order for metabolic pathways

Structure and Function of the Plasma Membrane

• Plasma membrane - outermost boundary of the cell
• Consists of lipids, protein, & carbohydrates
• Lipids (fats) are biochemicals characterized by their lack of water solubility
  • In the plasma membrane, they form a double layer in which many of the proteins float freely
• Human cells have thousands of different types of proteins
  • Each type is structurally and functionally unique
  • Proteins have four levels of structure
  • Amino acids join by peptide bonds, forming peptides (short chains of amino acids- building blocks of proteins) and proteins

Cell vs organelle membrane

• Different types of proteins inserted

Cell Structure - Membrane Transport

• Molecules move through the plasma membrane in five ways:
  • Diffusion- the movement of water molecules from high to low concentrations
    • Simple diffusion - goes directly through the cell membrane w/o the need for transfer proteins
  • Carrier proteins and Facilitated Diffusion/Transport
    • Carrier molecules help water molecules diffuse through membranes
  • Active Transport (facilitated transport, done by protein)- molecules are also actively transported across the membrane; against the transport gradient
    • Needs energy to move against it
    • Movement of molecules across membranes with:
      • The aid of protein carrier molecules in the plasma membrane
      • Energy supplied by ATP
    • ATP consists of 3 smaller molecules
      • Adenine
      • Ribose
      • 3 phosphate groups
    • When cells needs energy, ATP splits off a phosphate, forming ADP; the breaking of the phosphate bond yields energy that the cell can use directly (ATP → ADP + Pi + Energy)
    • Reactions that give off energy often turn the energy over to ADP, so new ATP can be formed (ADP + Pi → Energy + ATP)
  • Endocytosis - cell releases large membranes from its interior to the outside; done by fusing a vesicle containing this molecule within the cell membrane
    • Large molecules and cells are ingested by endocytosis; two types exist, phagocytosis (cells ingest large molecules and other cells) and pinocytosis (cells ingest extracellular fluids including dissolved materials)
  • Exocytosis - take something within and change its shape, expelling it
    • Cells regurgitate materials, releasing large molecules
• Osmosis- the diffusion of water across the plasma membrane
  • Situation: two fluids with different concentration of solute are separated by a selectively permeable membrane → result: the fluid will flow from one side to the other, moving down the concentration gradient
  • In humans, osmosis helps regulate the concentration of fluid surrounding the cell

Cellular Compartmentalization: Organelles

The Nucleus - nucleus houses the genetic information that controls the structure and function of the cell

Mitochondria - Mitochondria are the site of cellular energy production

• Double sided
• Drives formation of phosphate bonds
• Proteins of the electron transport system sit in there to make it easier for the reaction to go in a certain direction
• Unique- they have their own DNA
  • We inherit our own maternal DNA
  • Consume oxygen in the body to produce energy- looks like a cell (fits some descriptions of a living organism)
    • Theory: Maybe at one time they were an individual organism and combined with another organism that didn’t require oxygen
• Glucose breakdown takes place mostly in the mitochondrion
• Energy liberated from glucose molecules capture by ATP molecules
• Cellular energy production captures about 30% of the energy contained in glucose
  • The rest is given off as heat; increase rate of energy production (or metabolism) → increase in heat production
  • Muscles twitch when cold which helps generate some heat

Protein Production

• 3 organelles are involved in manufacturing protein
  • Endoplasmic reticulum- some proteins are produced by ribosomes on the surface of the rough endoplasmic reticulum
    • Proteins that are going to be imbedded or associated with membranes (like EPR) are made in the endoplasmic reticulum; membranes may gravitate towards surface
  • Ribosomes- involved in all protein synthesis
    • Free to roam around the cytoplasm
    • Where the RNA go to deliver the message about sequence that amino acids need to be put in order
  • The Golgi Complex - type of endoplasmic reticulum
    • The golgi sorts, modifies, and repackages proteins for extracellular use
    • Ex. peptides that act as hormones would be produced here (and merge in membrane to secrete peptide-type hormones)

Lysosomes

• Membrane-bound organelles that contain digestive enzymes
• Break down substances within the cell- digesting organelles, damaged protein (ex. due to heat) that have finished their purpose
• What's different? What the composition of their membrane is- after all how much phospholipid what type of proteins may or may not be embedded in that so that's one way to identify these different types of organelles
• Inside environment: Digestive enzymes and it also often much more acidic than the rest of the cell
  • Play a part in embryonic development

Cellular Movement

• Flagella - relate to sperm cells produced in the body; sticks out
  • Organelles that permit cellular motility
  • Wiggling type-option - provides locomotion to the cilia;
• Cilia - provides movement across the surface of cells and tissues; slender and projets from the much larger cell body
  • Primarily cilia may plan an important role in cellular communication
  • As things move across the surface and try to recognize what's out there we see them predominant in the digestive system and moving food particles and molecules across the membranes of the digestive system
  • Not common for human cells to move through it
• Some cells move by amoeboid motion
  • Seen earlier in endothelial cells where the membrane is sort of reaching out and then there's growth or movement to that area

Cell Cycle and Chromosomes

Cell Cycle - events between one cell division and the next

2 major stages:

1. Interphase - cell is not dividing but is very active ; cells just existing doing its normal work; functioning
   1. G₁ - cell grows and carries out basic functions
      1. Signals tell cell to divide, stop for repair or DNA, die or enter G₀
   2. Go or S- genetic material replicates (or dies)
   3. G₂ - cell prepares to divide and chromosomes begin to condense
   4. Prophase
   5. Prometaphase
   6. Metaphase
   7. Anaphase
   8. Metaphase
   9. Cytokinesis
2. Cell division - mitosis (copying of everything) and cytokinesis (the actual division)
   1. Nuclear and cytoplasmic division occur separately
      1. Requires two separate but related processes:
         1. Mitosis, or nuclear division
         2. Cytokinesis, or cytoplasmic division

Chromosome Duplication

• Entire genome (tells the cell everything there is to know about it and human body) must be duplicated before cell division
• In prokaryotic cells, genomes is single circular DNA molecule
• In eukaryotic cells, genome divided among multiple chromosomes housed in nucleus
  • Humans have 46, chickens have 78, rice has 24
    • **Statistically it’s more common for humans to have 46; it’s possible to have a different number → resulting in a functional difference that could be problematic from typical human lifespan (ex.

Chromosome

• Contain all of the genetic information required to control cellular activity
• Each organism has a set number of chromosomes
• All body cells, except the germ cells, are called somatic cells
• Somatic cells- containing full complement of chromosomes; they are diploid
• Germ cells (gametes- sperm and egg) contain 23 (half the number of chromosomes of somatic cells); they are haploid

Chromosomal Condensation - chromosomes condense after replication, which facilitates mitosis and allows for separation

• Condensed chromosomes are metabolically inactivity; you have to unwind them to read
• Chromatids- head of the chromosome
  • Made up of chromatin fiber - made up of …
  • Middle of structure Centromere
  • The # of chromatids varies (one or two)- depends on the stage of the cell cycle

Replication

• Before a cell divides, DNA must be replicated so each daughter cell gets the same set of genetic instructions
• Semiconservative - each new DNA strand is half old and half new DNA
• Uses an army of enzymes
  • DNA polymerase adds new nucleotides complementary to the bases on the exposed strands
  • It takes a protein to put the right nucleic acid in the right spot in the sequence
• Enzymes copy DNA simultaneously at hundreds of origins of replication → proceeds in both directions at once
• DNA polymerase can only work at 3’ (3 prime- moving from 5 to 3) end
  • Leading strand synthesized continuously - lagging strand requires ligase to put it back together (ligase joins Ozakazi fragments and seals nicks in sugar-phosphate backbone)
  • Lagging strand synthesized discontinuously forming Okazaki fragments- short segments of DNA that are created during DNA replication (formed on the lagging strand of DNA & are essential for cell division)
  • HUGE amount of energy required to make the copies - anytime there is movement or a rebinding, it takes energy
  • Very accurate but mutations do occur - skip, add, changed order of sequence in base pairs
    • Important as this creates new alleles (variants of genes);
• Helicase = unwinds DNA double helix
• DNA polymerase = adds new nucleotides to growing strands

DNA Condensation - DNA condenses into visible chromosomes before cell division

• Chromatid - one of 2 identical copies of a replicated chromosome
• Sister chromatids - pair with identical DNA sequence
• Centromere - point of attachment

Mitosis - 2/10

• Overall, the goal is to separate genetic material evenly between the 2 daughter cells
• Forms a mitotic spindle - consists of a centrosome (centriole and cloud of proteins- w microtubules reaching out to chromatid); pulls half to each new cell
• Centrosomes organize mitotic spindle
• Kinetochores attach chromosomes to the spindle

Phases of Mitosis

• Prophase - chromosomes condense, mitotic spindle begins to form → nuclear envelope breaks down
• Metaphase - chromosomes line up on mitotic spindle, middle of cell
• Anaphase - centromeres split, one chromatic of each pair pulled to opposite pole
• Telophase - mitotic spindle disassembles, chromosomes begin to unwind → nuclear envelope reforms

Cytokinesis - cell membrane pinches off → ending up with two new cells

• Animal cells - cleavage furrow results from contractile ring
• Plant cells construct a new cell wall

Cell Cycle Regulation

• Some cells divide more or less constantly (constant turnover)
• Signals to divide come from outside of the cell
• Growth factors → proteins stimulating cell division
• Checkpoints - ensure cell does not enter next stage until previous stage is complete

Telomeres - tips of eukaryotic chromosomes

• Lose nucleotides and become shorter at each cell division
• Cell division stops (most of the time) after about 50 cell divisions
• Telomerase - enzyme that keeps telomeres long
  • Cancer cells (Malignant)- Active telomerase so they are immortal (Immortal life of Henrietta Lacks- her cell division never stopped → cells would keep growing
  • Normal cells - Inactive telomerase so they die off when telomeres get short
• Apoptosis - a type of cell death in which a series of molecular steps in a cell lead to its death. The body uses this to get rid of unneeded or abnormal cells
  • Process of apoptosis may be blocked by cancer cells

Meiosis

• Sexual reproduction requires a fertilization event that occurs between two haploid cells (cells that contain a single set of unpaired chromosomes - 23, no duplicates of any of the chromosomes)
• All human cells outside gametes (sperm/egg) are diploid (contains two complete sets of each chromosome - one maternal (mother’s side) , one paternal (father’s side)
• Meiosis is the process of diploid cells undergoing meiosis two divisions to produce 4 haploid daughter cells

Meiosis I

• Prophase I - Chromosomes condense
  • Bivalents form - maternal & paternal replicated copies of each chromosome that will line up side by side on equator of cell
  • Crossing over can occur - exchange of maternal & paternal genetic info
  • Nuclear membrane breaks down
• Prometaphase I - spindle apparatus completes - a structure in eukaryotic cells that separates sister chromatids during cell division