Biology Keystone

The Cell

The Cell Theory

• All living things are made up of cells

• All living things function through the activities of their cells (metabolism)

• Cells come only from pre-existing cells

“Cell People”

• Schleiden: Plants are made of cells

• Schwann: Animals are made of cells

• Virchow: Cells come only from cells

• Hooke: Named the cell

• van Leeuwenhoek: Invented a crude microscope; first to see living cells

• Brown: Discovered the nucleus

Structure and Function

• Nerve cells have long processes to transmit information over long distances

Epithelial Cells (Skin)

• Epithelial cells are flat and platelike in order to form a protective covering over the organism

Prokaryotic Cells

• Lack an organized nucleus

• Lack membrane-bound organelles

• Usually have a cell wall

Plant Cells

• Have a cell wall

• Contain a large central vacuole

• Usually contain chloroplasts

Animal Cells

• Do not have a cell wall

• Have centrioles

• Have smaller vacuoles

• Have lysosomes

The Cell Wall

• Made of cellulose

• Gives support to the plant cell

• Gives strength to the plant cell

• Is permeable

Plasma Membrane

• Controls what enters and leaves the cell

• Made of a phospholipid bilayer

• Found in all types of cells

Cytosol

• The area of the cytoplasm outside of the individual organelles is called the cytosol

• The cytosol contains thousands of enzymes

• The cytosol takes molecules and breaks them down, so that the individual organelles can use them

The Nucleus

• Contains the cell’s DNA

• Is surrounded by its own nuclear envelope

• Often referred to as the “control center” of the cell

DNA

• The genetic material in the nucleus

• Double helix

• Forms chromatin (working DNA) and chromosomes (nonworking DNA)

Nucleolus

• The nucleolus is an approximately spherical region within the nucleus of eukaryotic cells

• It stores RNA and ribosomal subunits

Mitochondria

• Mitochondria generate the cell’s energy through cellular respiration

• Usually they are rod-shaped, however, they can be round

• The inner membrane is thrown into folds or shelves called cristae

• Mitochondria have their own DNA and ribosomes

• They are capable of reproducing themselves

• Humans inherit mitochondrial DNA only from the mother

• Powerhouses of the cell

• Site of cellular respiration

• Breakdown of food to release energy and generate ATP

Chloroplasts

• Chloroplasts are the site of photosynthesis, the process by which autotrophs make food

• Chlorophyll is the light-trapping pigment in the chloroplast

• Stroma is the semi-fluid filled space that contains enzymes

• Thylakoids are hollow sacs that provide membrane for photosynthetic reactions

• Grana are stacks of thylakoids

• Lamellae connect the grana

• Like mitochondria, chloroplasts have a double membrane, their own DNA, and ribosomes

• Chloroplasts can reproduce themselves

Ribosomes

• Granular organelles

• Site of protein synthesis

• Attached to the rough ER or located in the cytoplasm

• Manufactured in the nucleolus

• Made of RNA and protein subunits

Rough Endoplasmic Reticulum

• A complex network of membranes

• Bears the ribosomes during protein synthesis

• Processes and transports polypeptides to the Golgi complex

• Hollow interior is known as the “lumen”

Smooth Endoplasmic Reticulum

• Smooth ER is associated with the production and storage of lipids, especially steroids

• Releases calcium in cardiac and skeletal muscle cells so that contraction can occur

• Detoxifies alcohol and poisons in the liver and kidney cells

Golgi Apparatus

• Receives proteins from the rough ER

• Processes, packages, and delivers the proteins

• Packaging occurs via vesicles

• Responsible for packaging proteins for the cell

• Proteins produced by the rough ER pass into the Golgi cisternae

• These proteins are then squeezed off into vesicles (small vacuoles) for transport out of the cell

Lysosomes

• Found in animal cells

• Contains hydrolytic enzymes to digest almost everything in the cell

• Manufactured by the Golgi Apparatus

• Autophagy

  • Digestion of worn organelles

• Autolysis

  • Digestion of damaged or extra cells

Peroxisomes

• Not from the Golgi apparatus

• Neutralize free radicals (Oxygen ions that damage cells) in the liver and kidneys

• Detoxify alcohol and drugs

• Break down fatty acids for the mitochondria to use for energy

Glyoxysomes

• Found in some seeds

• Break down stored fats to provide energy for the developing plant embryo

Vacuole

• Large fluid-filled vesicle surrounded by a membrane

• Can store water, nutrients, wastes, and pigments

• Larger in plant cells

• Help plant cells create turgor, internal water pressure

Contractile Vacuoles

• Membrane-bound sac

• Plays roles in release of excess water from protists that live in watery environments

Other Vacuoles

• Amyloplasts

  • Store starch in plant cells

• Chromoplasts

  • Store pigments other than chlorophyll; give color to petals and leaves

Cytoskeleton

• For mobility and stability

• Primary types of fibers comprising the cytoskeleton are microfilaments, microtubules, and intermediate filaments

Centrioles

• In animal cells only

• Two cylinders at right angles to one another

• Close to the nucleus

• Help to form the spindle fibers for cell division

Flagella and Cilia

• Flagella are long and whiplike

• Cilia are short and hairlike

• Both are used for locomotion

• Cilia are also used internally to sweep cells or particles

Animal Cell

Plant Cell

Organic Compounds

Organic Compounds

• The Molecules of Life

• Made of

  • Carbon

  • Hydrogen

  • Usually Oxygen

    • Sometimes:

      • Nitrogen

      • Phosphorus

      • Sulfur

The Carbon Atom

• Has four valence electrons

• Forms strong covalent bonds

• Can form single, double, and triple bonds

• Likes to bond to itself

• Carbon compounds take many shapes such as:

  Chains

Branched Chains

Rings

Functional Groups

• Groups of atoms sometimes bond to carbon chains

• These “functional” groups give the carbon compound unique properties

  • Hydroxyl: OH

    

    Carbonyl: CO

    • 

  • Carboxyl: CO2H

    • (R is a placeholder)

      

  • Amino: NH2

    • 

  • Methyl: CH3

    • 

  • Phosphate: PO4H2

Building Organic Compounds

• Monomers are single units of an organic compound that have all the properties of the compound

• Polymers are large organic compounds consisting of several monomers bonded together

• Macromolecules refer to extremely large polymers

• Glucose is the monomer of starch, glycogen, chitin, and cellulose

Organic Compounds

• The four categories of Organic Compounds found in living things

  • Carbohydrates

  • Lipids

  • Proteins

  • Nucleic Acids

Carbohydrates

• Sugars

  • Used for energy

  • Produced by plants through photosynthesis

  • Simple sugars

• Made of Carbon, Hydrogen, and Oxygen

• The ratio of C:H:O is 1:2:1

• Monosaccharides are the monomers of carbohydrates

  • C6H12O6 is the formula for a monosaccharide

    • Glucose: blood sugar

    • Fructose: fruit sugar

    • Galactose: found in milk

• Disaccharides

  • Are built from two monosaccharides

  • C12H22O11 is the general formula

    • Sucrose: table sugar; sweet

    • Lactose: milk sugar; nourishment for young mammals

    • Maltose: sugar in seeds; nourishment for embryo plants

      • Glucose + Glucose = Maltose + H2O

      • Glucose + Fructose = Sucrose + H2O

      • Glucose + Galactose = Lactose + H2O

• Polysaccharides

  • Large molecules (polymers)

  • Made of many monosaccharides bonded together

    • Starch: energy storage in plants

    • Glycogen: energy storage in animals

    • Cellulose: cell wall construction

    • Chitin: cell walls in fungi and exoskeletons in arthropods

• Isomers

  • Compounds that have the same molecular formula but different structures are called isomers

  • Each isomer has its own properties because the shape of the molecule determines its characteristics

  • Shape determines properties

• Condensation Reaction (Dehydration Synthesis)

  • Building a large organic molecule from two smaller organic molecules by removing a molecule of H2O through a process called condensation reaction

  • The water is produced by removing an OH group from one molecule and a H from a hydroxide group in the other molecule

• Hydrolysis

  • The breaking of polymers into monomers through the addition of water

Lipids

• Made of Carbon, Hydrogen, and Oxygen

• Monomers are glycerol and fatty acids

• The high Carbon:Hydrogen ratio enables the molecules to store more energy than carbohydrates

  • Fatty Acids

    • Made of long hydrocarbon chains

    • Attached to a carboxyl functional group

    • Saturated Fatty Acids

      • Have only single Carbon to Carbon bonds

      • Fatty acid tails are straight

      • Can cause Cardiovascular disease

      • The bad fat

    • Unsaturated Fatty acids

      • Have one or more double Carbon to Carbon bonds

      • Fatty acid tails are “kinked”

      • Less likely to cause cardiovascular problems

      • The good fat

    • Unsaturated fats are liquid at room temperature

    • Olive oil and corn oil are unsaturated fats

    • Most saturated fats are solid at room temperature

    • Butter and lard are saturated fats

      • Coconut oil is an exception

    • Trans Fat

      • The new health threat

Types of Lipids

• Triglycerides

  • 3 fatty acids:1 glycerol

  • Used for insulation under the skin and around organs

  • Store energy for future use

• Phospholipids

  • Composed of

    • Two fatty acids

    • One glycerol

    • One phosphate group

  • Phospholipid Structure

    • Hydrophilic head

    • Hydrophobic tails

    • The unsaturated fatty acid tails create kinks that enable the phospholipid to spin freely

  • Allow our membranes to be fluid

• Steroids

  • Chemical messengers

  • Composed of four fused Carbon rings

  • Cholesterol

    • Keeps membrane’s fluid at low temperatures

    • Stabilizes membranes at high temperatures (keeps them together)

  • Estrogen and Testosterone

    • Responsible for the development of secondary sexual characteristics

• Waxes

  • Waterproof

    • Form a protective coating on plants

    • Form protective layers in animals

      • Earwax prevents bacteria from entering the ear

Proteins

• Made of Carbon, Hydrogen, Oxygen, and Nitrogen

• Monomers are called amino acids

• Amino acids are help together by peptide bonds

• Amino Acids

  • Essential

    • Cannot be made by the body

    • Must be supplied in the diet

  • Nonessential

    • Can be made by the body

  • Ex:

    • 
      

      

  • The alpha carbon is in the center

  • A hydrogen atom, a carboxyl group (acid group), and an amino group are bonded to the alpha carbon in all amino acids

  • The rest of the amino acid referred to as the “R” group is unique to each of the 20 amino acids

• Condensation Reaction

  • Polypeptide is the name given to protein polymers

  • They can be built by removing a molecule of water from every two amino acids bonded together

  • Peptide Bonds

    • H is removed from the amino group of one amino acid, and the OH is removed from the carboxyl group of the other amino acid

• Hydrolysis

  • Polypeptides can be broken down into amino acids by adding back the H2O

• Structural Proteins

  • Uniquely made in each person

  • Used for skin, hair, nails, muscles, bones

    • Examples: collagen and keratin

• Transport Proteins

  • Found in the cell membrane to bring molecules in and out

  • Some are unique to particular cells

    • Example: Hemoglobin- carries oxygen

• Messenger Proteins

  • Hormones are chemical messengers

    • Example: Insulin- regulates blood sugar

• Motile Proteins (Mobility)

  • Found in cytoskeleton and muscles

    • Examples: actin and myosin

• Storage Proteins

  • Proteins that remain in supply for growth and development

    • Example: egg white

• Defense Proteins

  • Antibodies fight specific infections

• Enzymes

  • Controls every activity in the cell

  • Speed up reactions at least one-million times

  • Examples: lactase and sucrase

• Heat can change protein structure

• Other agents that denature proteins are:

  • Extreme pH

  • Exposure to Lead (Pb) and Mercury (Hg)

Nucleic Acids

• Made of monomers called nucleotides

  • One 5-Carbon sugar

  • One phosphate group

  • One Nitrogen base

• DNA

  • Transmits genetic information from one generation to the next

  • Contains the information necessary to tell the cell how to make proteins

  • The genetic material in the nucleus

  • Double Helix

  • Forms chromatin and chromosomes

  • Sugar in DNA is deoxyribose

  • Always in a double strand called a helix

  • Has four bases:

    • Adenine

    • Thymine

    • Guanine

    • Cytosine

• Watson and Crick

  • Used the research of many people

  • Put together the double helix model of DNA

  • Won the Nobel Prize with Wilkins for the model

• Rosalind Franklin

  • Took the x-ray pictures of DNA that enabled Watson and Crick to figure out the double helix model

  • Died before the Nobel Prize was awarded

• RNA

  • Copies the DNA genetic code

  • Controls protein synthesis according to directions from DNA

  • Sugar in RNA is ribose

  • Exists as a single strand

  • Has four bases:

    • Adenine

    • Uracil

    • Guanine

    • Cytosine

• ATP

  • Adenosine Triphosphate

  • Composed of

    • Adenine- a nitrogen base

    • Ribose- a five carbon sugar

    • Three phosphate groups

  • The molecule is the energy storage mechanism for all living things

  • Recycling ATP

    • When energy is needed, the cell breaks down ATP molecules

    • ATP → Energy + ADP + Phosphate

    • During cellular respiration, energy is released and used to replace the phosphate

    • ADP + Energy + Phosphate → ATP

Embedded Proteins

The Cell Membrane

• Regulates what goes in and out of the cell

• Protects the cell

• Communication (with other cells)

Fluid Mosaic Model

• Proteins embedded in the cell membrane:

  • Enzymes are chemicals that catalyze biochemical proteins

  • Receptor proteins: The receptor proteins are always found on the outer cell membrane surface. This is where hormones and neurotransmitters and other chemicals attach (binding site) to the surface of the cell. We know hormones affect the activity of the cells.

    • Ex: Insulin regulates glucose

  • Ion Channels: ion channels are a very narrow tube-shaped protein that help establish a tiny pore in the cell membrane. They are only large enough to allow an ion to go through. Each ion channel is for specific ions. They can open and close and are very important in understanfing the rest of physiology.

    • Ex: “Calcium channel blockers” are important in regulating blood pressure

  • Transport/Carrier Proteins are embedded in the cell membrane to help transport glucose and amino acids across the membrane. These molecules are too large to go through ion channels.

  • Glycoproteins have carbs attached to the protein which are used as cell surface markers. Key in transplantation.

  • Sodium-Potassium Pump (carrier protein) is a pump which moves 3 sodium ions out of the cell for every 2 potassium ions that enter the cell

  • Aquaporin: small proteins that allow for osmosis to occur

• Cholesterol helps maintain the cell’s firmness and integrity

Functions of Receptor Proteins

• Changes in Permeability

  • The binding of a signal molecule to the receptor protein causes an ion channel to open, allowing specific ions to cross the cell membrane

• Second Messengers

  • The receptor protein may cause the formation of a second messenger inside the cell. The second messenger acts as a signal molecule and amplifies the signal of the first messenger, that is, the original signal molecule

• Enzyme Action

  • The receptor protein may act as an enzyme. When a signal molecule binds to the receptor protein, the receptor protein may speed up chemical reactions inside the cell

Easiest type of molecule to cross the cell membrane: Small, Nonpolar

Cell Transport

Diffusion

• One way cells maintain homeostasis is by controlling the movement of substances across their cell membrane

• Cells must use energy to transport some substances across the cell membrane

• Other substances move across the cell membrane without any use of energy by the cell

Random Motion & Concentration

• Passive Transport

  • Movement across the cell membrane that does not require energy from the cell

• Concentration Gradient

  • A difference in the concentration of a substance, such as the balls, across a space

• Equilibrium

  • A condition in which the concentration of a substance is equal throughout a space

• Diffusion

  • The movement of a substance from an area of high concentration to an area of lower concentration caused by the random motion of particles of the substance

  • Many substances, such as molecules and ions dissolved in the cytoplasm and in the fluid outside cells, enter or leave cells by diffusing across the cell membrane

• Osmosis

  • The diffusion of water through a selectively permeable membrane

  • Like other forms of diffusion, osmosis involves the movement of a substance, water, down its concentration gradient

  • Osmosis is a type of passive transport

  • Hypertonic solution

    • Water moves out. When water diffuses out of the cell, the cell shrinks.

  • Hypotonic solution

    • Water moves in. When water diffuses into the cell, the cell swells.

  • Isotonic solution

    • No net water movement. A solution that produces no change in cell volume.

Diffusion Through Ion Channels

• An ion channel is a transport protein with a polar pore through which ions can pass

• The pore of an ion channel spans the thickness of the cell membrane

• An ion that enters the pore can cross the cell membrane without contacting the nonpolar interior of the lipid bilayer

Electrical Charge and Ion Transport

• The movement of a charged particle, such as an ion, across the cell membran is also influenced by the particle’s positive or negative electrical charge

• A more positively charged ion located outside the cell is more likely to diffuse into the cell, where the charge is negative

• A more negatively charged ion located inside the cell is more likely to diffuse out of the cell

Facilitated Diffusion

• Most cells also have a different kind of transport protein, called carrier proteins, that can bind to a specific substance on one side of the cell membrane, carry the substance across the cell membrane, and release it on the other side

• Definition: when carrier proteins are used to transport specific substances, such as amino acids and sugars, down their concentration gradient

Movement Against a Concentration Gradient

• Active Transport

  • The transport of a substance across the cell membrane against its concentration gradient

  • Unlike passive transport, active transport requires the cell to use energy because the substance is being moved against its concentration gradient

  • Most often, the energy needed for active transport is supplied directly or indirectly by ATP

• Sodium-Potassium Pump

  • One of the most important membrane pumps in animal cells is this carrier protein

  • In a complete cycle, the Na-K pump transports three sodium ions, Na+, out of a cell and two potassium ions, K-, into the cell

  • The Na-K pump has four steps:

    • Three sodium ions inside the cell bind to the sodium-potassium pump

    • The pump changes shape, transporting the three sodium ions across the cell membrane and releasing them outside the cell

    • Two potassium ions outside the cell bind to the pump

    • The two potassium ions are transported across the cell membrane and are released inside the cell

Movement in Vesicles

• Many substances, such as proteins and polysaccharides, are too large to be transported by carrier proteins. These substances are moved across the cell membrane by vesicles

• Endocytosis is the movement of a substance into a cell by a vesicle

• Exocytosis is the movement of a substance by a vesicle to the outside of a cell

Membrane Receptor Proteins

• Cells must also respond to important information and filter out unimportant information

• Cells can receive the messages carries by certain signal molecules because the cell membrane contains specialized proteins, called receptor proteins, that bind these signal molecules

• Receptor protein is a protein that binds to a specific signal molecule, enabling the cell to respond to the signal molecule