Biology Test Unit 2

What is a cell?

What is a cell?

• Smallest unit of structure and function in all living things- Enclosed by membranes that maintains an internal environment separate from external environment

Prokaryotes and Eukaryotes similarities

1. DNA (genetic material/hereditary material & RNA)

2. 2. ribosomes (protein synthesis)

3. 3. cytoplasm (most metabolism occurs here)

4. 4. plasma membrane (phospholipid bilayer)

Prokaryotes

• no nucleus- no membrane-bound organelles- has one circular chromosome DNA- bacteria only (archaebacteria & eubacteria)- all have cell wall

Eukaryotes

• has nucleus/nuclear envelope- membrane-bound organelles- multiple linear chromosomes- all other organisms (protist, fungi, plant, animal)- animal cells have no cell walls

Prokaryotes X energy efficiency

Due to very small size they have a very high surface area to volume ratio (100X smaller so my name is bella hadid) resulting in very fast metabolism and reproduction

Eukaryotes X energy efficiency

Maintain efficiency by use of membrane bound organelles (compartmentalization)

Energy efficiency

• High surface area to volume ratio

• Small cells have a larger SA (lots of membrane and contact with environment) and smaller volume (less cytoplasm to feed) = more efficient exchange rate with environment

• Specific cellular structures are used to maximize exchange of materials with the environment (these structures increase surface area without increasing volume)

Specific cellular structures to increase surface area

• Root hairs: thin extensions of root that increase surface area for water/mineral absorption

• Alveoli: thin, small sacs in lungs to increase surface area to maximize gas exchange

• Villi and microvilli (filled w/ microfilaments): finger like projections of small intestine to increase surface area to increase absorption of nutrients into bloodstream

As volume within a cell increases

number of reactions required to maintain cell efficiency increases

As a cell grows, SA:V ratio __________ because volume cubed ___________ _________ than SA squared

decreases, increases faster

At some point, SA:V ratio becomes so small that SA is too small (not enough contact with environment) to supply raw materials required to maintain cell's metabolic needs so cells......

1. Undergo apoptosis (cell death)

2. 2. Make more organelles

3. 3. Divide into 2 smaller cells

Advantages to compartmentalization (membrane bound organelles)

• All materials/enzymes together and ready to use; specialization and efficiency of each cell

• Allows for specialization of cells and more complex organisms without sacrificing efficiency-- Lots of mitochondria ---> muscle cells-- Lots of golgi bodies ---> endocrine cells that secrete

• Different reactions can occur simultaneously without disruption from other reactions

• Protects cytoplasmic proteins and DNA in nucleus to be protected and not degraded by enzymes from peroxisomes and lysosomes

Endosymbiotic theory

Explains how eukaryotes evolved from prokaryotes

According to this theory

1. Small, aerobic prokaryotic cells were engulfed by larger prokaryotes (endocytosis)

2. Rather than digesting the smaller cell, the 2 cells formed a mutualistic symbiotic relationship. The host cell helped provide nutrients and the internal cell helped to produce energy.(developed oxygen using internal membrane bound organelle: mitochondria)

3. Eventually, the 2 cells became interdependent to survive

Later a photosynthesizing prokaryote got engulfed in the same way becoming the _____________

chloroplast

Evidence of endosymbiotic theory

Mitochondria & chloroplasts are membrane bound organelles that:

1. are similar in size and shape to prokaryotes

2. 2. each have their own set of circular DNA and ribosomes (like prokaryotes)

3. 3. double membranes (showing endocytosis occurred)

4. 4. divide independently (not when the rest of the cell divides)

Some prokaryotic cells engulfed were blue-green algal cells which became

chloroplasts performing photosynthesis

The oxygen utilizing bacteria became

mitochondria performing cellular respiration

Organelles only in eukaryotes

• ER- nucleus- lysosome (animal only)- centrosome (animal only)- golgi apparatus- mitochondria- vacuole- nucleolus- chloroplasts (plant only)- nuclear membrane- cytoskeleton

Organelles in eukaryotes and prokaryotes

• plasma membrane- cytoplasm- ribosomes- cell wall (plant only)- DNA

Endoplasmic reticulum

• series of membrane tubes that allows materials to travel

• smooth: without ribosomes (synthesizes lipids like phospholipids, cholesterol, fatty acids), involved in detoxification of drugs/alcohol, stores Ca for cell signaling and muscle contraction

• rough: with ribosomes (synthesizes proteins to be shipped out of cell)

Nucleus

• serves as control center for cell metabolism and reproduction- double envelope openings: nuclear pores- contains genetic material (DNA)- components: chromosomes/chromatin, nucleolus

Lysosome (animal only)

• membrane enclosed organelle- components: hydrolytic enzymes (digestive enzymes)- break down nutrients, digest old cell parts, digest bacteria and viruses in white blood cells

Centrosome (animal only)

• make microtubules (spindle fibers) during mitosis (attach and arrange chromosomes)

Golgi apparatus

• packages, stores, secretes products of cells- protein processing (protein can be changed here) and sorting

Mitochondria

• performs respiration/releases energy (ATP) from food molecules- double; inner contains enzymes for ATP production

Vacuole

• components: pigments, food, oils, carbs, water, toxins/waste- membrane-enclosed organelle- storage- animals: have many small ones- plants: one or two large central

Nucleolus

• production of ribosomes inside nucleus

Chloroplasts (plant only)

• site of photosynthesis- double membrane- components: pigments (chlorophyll), enzymes catalyze oxidation-reduction reactions- produces ATP and sugars for plant cells

Nuclear membrane/envelope

• controls movement into and out of nucleus- contains pores

Cytoskeleton

• three proteins in cytoplasm help give structure to the cell and aid in cell movement1. microtubules2. microfilaments3. intermediate fibers

Structural evidence to support common ancestry of all eukaryotes

cytoskeleton, endomembrane system, nucleus

Microtubules

• long, hollow tubes made of protein tubulin- form rigid skeleton- provides framework for organelles/vesicles to move within cell (uses motor proteins)- spindle fibers (from centrosomes used to separate chromatids during cell division)- found in: centrioles/centrosomes, flagella, cilia

Microfilaments

• thinnest, threadlike strands of contractile protein actin- attach to inside of cell membrane allowing movement- cyclosis/cytoplasmic streaming moving cytoplasm by contracting and relaxing- microfilaments form pseudopods- found in: microvilli extensions

Intermediate fibers

• fibrous, rope-like, protein keratin- stabilizes a cell's structure by resisting tension (prevents tearing of tissues)- helps anchor nucleus and other organelles- found in: hair and fingernails

Plasma membrane

• selectively permeable nonpolar barrier (maintains homeostasis by controlling movement into and out of cell)- components: phospholipid bilayer with membrane proteins (aka integrins, transmembrane proteins, integral proteins)- polar heads- nonpolar fatty acid tails- fluid mosaic model: lateral movement and bobbing of membrane proteins within phospholipid components

Cytoplasm

• watery material/gel which contains many of materials (nutrients & ions) involved in cell metabolism

Ribosomes

• components: RNA and proteins- protein synthesis- no membrane- free floating ribosomes make proteins/enzymes that stay/work inside cell

Cell wall (plant only)

• gives cells shape/structure and protection- outside cell membrane- plants: cellulose (carb fibers)

DNA

• genetic material- eukaryotes: multiple, linear- prokaryotes: sinlgle, circular

Membrane Transport

transport of nutrients, ions, and secretory substances (like enzymes and hormones) from one side to the other is a major function of the cell membrane

Factors that determine how or if a substance will cross the cell membrane

1. polarity/charge (nonpolar, uncharged molecules can pass through easily)

2. size (still must be uncharged and nonpolar to pass without a protein channel)

3. concentration gradient (ions/molecules move down or with the concentration gradient without energy)

4. does it need a receptor (LDL) or protein channel (glucose)

Structure and functions of ECM

• support: collagen, fibronectin, proteoglycans- adhesion (cell-to-cell and outside-of-cell to inside-of-cell): fibronectin, proteoglycans- regulation (coordination & communication): fibronectin, proteoglycans- movement: fibronectin, proteoglycans

Cholesterol (animal cell membranes)

• at low temperatures: increases membrane fluidity by preventing membrane lipids from packing close together- at high temperatures: decreases membrane fluidity by decreasing the movement of membrane

Integrin/integral proteins

embedded in plasma membrane; transmit signals between ECM and cytoskeleton

Functions of membrane proteins

6 functions TIRES T - transport I - identity markers R - receptor E - enzymes S - structure

Transport proteins

• protein channels and carriers (passive)- protein pumps (active)- moves substances across membrane

Enzymes

catalyzes reactions (active site faces cytoplasm)

Identity markers

carbohydrates antenna detect surroundings (cell-to-cell recognition; self vs. non-self)- glycoprotein: short polysaccharide attached to protein- glycolipid: short polysaccharide attached to phospholipid if an antigen enters the body, glycoproteins are not recognized and immune attack will occur

Receptors

receives external signals from ligands (hormones, ions, neurotransmitters) and sends information into cell causing signal transductions (a specific response inside the cell)

Cell junction

uses peripheral and integral proteins connecting one cell to another (anchoring junctions, gap, and tight junctions)

Structure

attachment to cytoskeleton (microtubules and microfilaments) and extracellular matrix (outside of cell) maintain shape; includes the peripheral proteins

Protein processing and secretion

Step 1 (inside nucleus)

DNA (order of nucleotides) transcripts (copies) to mRNA (final edited)

Step 2 (leaving nucleus)

mRNA transcript leaves nucleus through nuclear pores and attaches to a ribosome (translation) on rough ER OR free floating ribosome

• rough ER: protein will modified and transported from inside lumen- free-floating: protein stays in cell

Step 3

protein is transported to transport vesicle

Step 4

golgi apparatus receives incoming protein at cis end then packages and prepares protein for secretion at trans end

Step 5

secretory vesicles (with final protein) fuse with cell membrane, releasing protein (enzymes, hormones, antibodies, neurotransmitters) outside cell (exocytosis) into blood stream or any cavity- if vesicle stays in cell ---> lysosome

Lysosomal storage disorders

genetic disorders that cause lysosomes to be missing one functional enzyme

Blood types are named for

glycoproteins (antigens) found on the surface of red blood cels

Each blood type can only recognize

its own proteins

To protect itself from foreign proteins entering the body, each blood type makes special ___________________

plasma proteins (antibodies)

Antibodies

proteins made by white blood cells that attack and kill antigens that body doesn't recognize found in blood plasma "binding sites attack" antibody produced and reacts to presence of antigen never fit with its own red blood protein (when an antibody fits into the red blood cell protein clumping/agglutination occurs = clots in blood vessel = death)

Antigens

glycoproteins on the surface of red blood cells "markers"

Type A

antigen/glycoproteins: protein Aproteins not recognized: protein Bplasma proteins made/antibodies: anti-B

Type B

antigen/glycoproteins: protein Bproteins not recognized: protein Aplasma proteins made/antibodies: anti-A

Type AB

antigen/glycoproteins: protein A and protein Bproteins not recognized: noneplasma proteins made/antibodies: none

Type O

antigen/glycoproteins: noneproteins not recognized: protein A and protein bplasma proteins made/antibodies: anti-A and anti-B

Rhesus (Rh) factor

inherited trait that refers to a specific protein found on surface of red blood cells

Passive transport

• no energy required to move substance across membrane down gradient [high] --> [low]^^ energy is released (entropy increases) used to do work inside cell- diffusion and facilitated diffusion

Diffusion (passive)

• small, uncharged, nonpolar (lipid soluble) molecules pass through easily- ex. O2, CO2, alcohol, cholesterol

When do molecules stop moving?

At equilibrium: equal number of molecules on both (no more gradient)

• molecules are in constant motion and will always move across membrane but no net movement occurs once equilibrium is reached

Facilitated diffusion (passive)

• medium, charged ions, polar molecules use protein channels/carriers to get through membrane (inside channel is hydrophilic/charged)- ex. K+, Na+, amino acids, glucose, Cl-- osmosis: movement of water across membrane---> water is polar so must use transport proteins (aquaporins)

Entropy

measure of disorder

Active transport

• requires energy (ATP) to move substance across membrane^^ energy is required (entropy decreases) increasing order- no gradient required [low] --> [high]- protein pumps and bulk transport

Protein pumps

• move ions across membrane to higher concentration against electrochemical gradient- uses ATP to change shape of protein pump- ex. Na+/K+ pump (animal), H+ pump (bacteria, plants)- create difference in charge across membrane: membrane potential--- cells always have relative negative charge inside of cell; outside is positive---- maintaining membrane potential is crucial for nerve conduction

Bulk transport

• large, bulky molecules across membrane using exocytosis (protein secretion) or endocytosis (phagocytosis/pinocytosis)- ex. starch, proteins, bacteria

Exocytosis

• move materials out of cell using secretory vesicles (secretory vesicle fuses with membrane to release product requiring energy)

Endocytosis

• move materials into cell (nonspecific process: does not require receptors or specific molecules)- phagocytosis: moves solids into cell using pseudopods- pinocytosis: moves liquids into cell

Receptor mediated endocytosis

• require specific receptor proteins that only endocytose a specific molecule (ligand) that activate receptors- ex. LDL (cholesterol + protein), insulin

LDL and endocytosis

body cells remove bad LDL cholesterol from circulating in blood by receptor mediated endocytosis: vesicle filled with LDL will fuse with lysosome to break down bad cholesterol

Hypercholesterolemia

• recessive genetic condition where there are no functional LDL receptors HH --> normal for LDL receptorsHh --> half the amount of functioning LDL receptorshh --> no functioning LDL receptors

How glucose gets into cell

1. insulin activates receptor in membrane causing signal transduction

2. 2. glucose channel proteins fuse with membrane

3. 3. glucose channels allow glucose in lowering blood glucose levels

4. 4. insulin receptors are endocytosed by receptor mediated endocytosis, breaking down insulin, fusing back to membrane to replace receptors in membrane

Cotransport

Secondary active transport across biological membrane in which transport protein couples movement of ion (usually Na+ or H+) down electrochemical gradient to movement of another ion or molecule against a concentration or electrochemical gradient

• Energy released from H+ moving down its gradient is harnessed to pull sucrose across membrane at the same time against its gradient

Cell junction

• plasmodesmata: channels between adjacent plant cells that allow chemical messages and nourishment to be shared- animal cells lack cells walls but most secret extracellular matrix that helps hold cells together

3 types of junctions in animal cells

1. tight junctions

2. 2. anchoring junctions/desmosomes

3. 3. gap junctions

Tight junctions

bind cells tightly, leakproof (ex. epithelial cells that line blood vessels, digestive tracts, or any covering/linings)

Anchoring junctions/desmosomes

fasten cells together with cytoskeletal fibers allowing stretching (ex. muscles and skin)

Gap junctions

allows neighboring cells to exchange signals and materials (ex. ions are sent through gap junctions for nerve cells to fire) like plasmodesmata!