cell physiology

Question 1

Describe the basic structure of the plasma membrane

Answer 1

surrounds the cell and most intracellular organelles.

- consists of a double layer of lipid molecule with embedded proteins (called phospholipid bilayer)

Question 2

What molecules make up the plasma membrane? Describe each in detail

Answer 2

Consists of phospholipids, cholesterol and glycolipids along with carbon and oxygen as primary molecules.

• Phospholipids are amphipathic with polar head groups and non polar tails.
• Cholesterol is a steroid that is also amphipathic and maintains cell fluidity (prevents phospholipids from touching each other)
• Glycolipids are lipids with a small CHO chain attached (also amphipathic) and form glycocalyx which is involved with identification and interaction between cells

Question 3

What is the function of the plasma membrane? (4 things)

Answer 3

1. Physical barrier (keeps organelles and proteins inside the cell, maintains fluid composition and homeostasis/ pH balance)
2. Cell-to-Cell communication (contains receptors that bind to specific signalling molecules arriving at cell surface)
3. Structural support (contains cell junctions and connections between plasma membranes or between membranes and ECF materials)
4. Transport (selectively permeable)

Question 4

What is the function of the organelle membrane?

Answer 4

they reflect different functions of cells or organelles and have different content of lipids and proteins

Question 5

What are the functions of desmosomes? What is its structure?

Answer 5

desmosomes are adhering junctions that anchor cells together in tissues that are subject to considerable stretching (like heart muscles)
- they are made up of the following proteins:
1 . plaques —> anchoring point for cadherins
2. Cadherins–> link cells together
3. Intermediate filaments –> structural supper and to anchors cytoskeleton of one cell to another to share the stress of stretching

Question 6

What are the functions of tight junctions? What is its structure?

Answer 6

Tight junctions are found in epithelial tissue

• involved in molecular transport
• consist of:
  1. occluding (link adjacent cells together to form impermeable function and limits movement of molecules between cells so molecules pass THROUGH cells instead)
• essential for polarized cells

Question 7

What is the function of gap junctions? What is its structure?

Answer 7

gap junctions are transmembrane channels linking cytoplasms of adjacent cells

• allows small molecules and ions to move between cells
• are made up of connexions

Question 8

What is the basic function and structure of the nucleus?

Answer 8

basic function of the nucleus is transmission of genetic material and contains information for protein synthesis
Has:
- nuclear envelope (porous)
- nuclear pores
- nucleolus (where RNA synthesis occurs)
and
Chromatin (DNA associated w proteins)

Question 9

what is basic function and structure of endoplasmic reticulum?

Answer 9

The rough ER:

• synthesis of proteins with bound functional ribosomes
• water soluble proteins, transmembrane proteins and post-translational modification of proteins
• Granular, with ribosomes on its surface
• flat

The smooth ER:

• synthesizes lipids, stores Calcium and involved in drug detoxification in liver cells
• argranular, with no ribosomes
• tubular

Question 10

What is the basic function and structure of Golgi apparatus?

Answer 10

Composed of cisternae which have many vesicles.
- sorts and packages proteins
it preforms post translational modification on them and then packages them up in vesicles and sends them to their destination

Question 11

What is the basic function and structure of lysosomes and peroxisomes?

Answer 11

lysosomes are digestive enzymes that are hydrolytic (break down large molecules to their smaller subunits)

• function at pH 5.0
• recycle organelles and destroy endocytose bacteria and viruses

Peroxisomes

• use oxygen to remove hydrogen from molecules
• a lot in kidney and liver
• breaks down a toxic called = 2H2O2 —> 2H2O + O2

Question 12

What is the basic function and structure of mitochondria?

Answer 12

is the cell’s powerhouse, and consists of a double membrane and is involved in cellular respiration (production of ATP from oxygen)

Question 13

What are two non membranous structures?

Answer 13

Ribosomes and cytoskeleton

Question 14

What is the function and structure of ribosomes?

Answer 14

Ribosomes are non-membrane bound and they are involved in protein synthesis
they have two subunits called small and large and stye are composed of RNA
The two major types of functional ribosomes are free ribosomes and ribosomes bound to rough ER

Question 15

What is the function and structure of cytoskeleton?

Answer 15

non-membrane bounce and is made up of protein filaments that sit in the cytoplasm.
- they maintain cell shape, maintain organelle positions and mediate cell and organelle motility (flagella)

Question 16

What compromises the cytosol?

Answer 16

• Water, high potassium concentration, and low sodium concentration.
• High protein concentration. Carbohydrates, amino acids and lipids.
• Inclusion bodies (storage granules for triglycerides)
• Secretory vesicles (move to surface of cell when hormone needs to be released).

Question 17

What are the different forms of vesicular transport? Define endocytosis and the three types of endocytosis? Define exocytosis?

Answer 17

Endocytosis --> uptake of material into a cell via vesicles that pinch off from cell membrane
The three types of endocytosis are:
1. Phagocytosis "cell eating"
2. Pinocytosis "cell drinking"
3. Receptor-mediated endocytosis

Exocytosis is the release of material from the cell via vesicles that fuse with the cell membrane

Question 18

What are the three driving forces of non-vesicular transport?

Answer 18

1. Chemical
2. Electrical
3. Electrochemical

Question 19

Describe chemical driving forces

Answer 19

when molecules flow passively down their concentration gradients (from high to low concentration). As size of gradient increases, the rate of transport of substance increases.

Question 20

Describe electrical driving forces

Answer 20

when the cell’s membrane potential (difference in electrical potential or voltage across cell membrane) causes flow of certain ions into or out of the cell.

Question 21

Describe electrochemical forces

Answer 21

the sum of electrical and chemical driving forces acting on ion. Direction depends on net direction of electrical and chemical driving forces

Question 22

Define simple diffusion

Answer 22

Passive movement of molecules through a biological membrane’s lipid bilayer. it does not require energy

Question 23

What factors determine if a substance can cross a membrane by simple diffusion?

Answer 23

1. solubility in lipid (polar or non polar)
2. Size (smaller diffuse more readily)
3. High to low concentration

Question 24

What factors influence the rate of simple diffusion? Describe each

Answer 24

1. Magnitude of driving force
2. Membrane surface area (higher the Sa, the higher rate of SD)
3. Membrane permeability –>
   - non polar cross easily
   - smaller and more regularly shaped diffuse faster
   - increasing temperature increases diffusion rate
   - rate of diffusion inversely proportional to the distance (thicker membrane is longer time to diffuse)

Question 25

Which factor is most important in determining if a substance can cross a membrane by simple diffusion?

Answer 25

Lipid solubility of diffusing substances

Question 26

What are the two types of facilitated transport and what do they have in common?

Answer 26

The two types are carriers and channels. They are both passive transport (does not require energy)

Question 27

What is the difference between the movement of molecules across plasma membranes via carrier and via a channel?

Answer 27

carrier mediated facilitated diffusion is when the protein in the membrane undergoes a conformational change to allow binding of a molecule and is continuously working until concentrations on each side of membrane are equal - does not require energy Channel mediated facilitated diffusion - selective and involves electrochemical gradient that determines the ion flux coming in or out - can be voltage gated, ligand gated, or mechanically gated (stretch or swell to open) - channels need something to open it

Question 28

What is the difference between primary and secondary active transport? provide an example of each

Answer 28

Primary active transport DIRECTLY hydrolyses ATP ( ATP --> ADP + pi) - an example is the sodium potassium pump

Question 29

What is the difference between saturable and non saturable transport?

Answer 29

Secondary active channels use electrochemical gradients from another ion channel that is moving an ion down its electrochemical gradient. involves cotransport, counter transport (symport and anti port)

Question 30

Define single transduction?

Answer 30

sequence of events between the binding of the molecule to the receptor and the production of a cellular response

Question 31

Define the role of first and second messengers

Answer 31

- First messengers is an extracellular chemical messenger that binds to a specific membrane receptor - Second messengers are substances that enter or are generated in the cytoplasm of a cell in response to the binding of an extracellular messenger

Question 32

What is the difference between lipid-solvable and lipid-insolvable chemical messengers? Where are the receptors located to which they bind?

Answer 32

Lipid soluble messengers can diffuse through the plasma membrane while lipid-insoluble (water-soluble) messengers need protein (receptors) to cross membrane. - lipid soluble chemical messengers bind to receptors in cytosol or nucleus (straight to the point) - lipid insoluble chemical messengers bind to receptors on extracellular surface of plasma membrane (channel-linked receptors, enzyme linked receptors and g-protein linked receptors)

Question 33

How do lipid-soluble chemical messengers produce an effect in the cell?

Answer 33

alter the transcription of mRNA by binding to response element and they alter the rate of synthesis of a particular protein (either increases or decreases mRNA responsible for a particular protein)

Question 34

What are two mechanisms of intercellular communication (between cells)?

Answer 34

Direct --> gap junctions and Indirect --> chemical messengers (incl. lipid-soluble or lipid-insoluble (water soluble)

Question 35

What are 3 properties of receptors?

Answer 35

1. Specificity --> binds to specific ligand 2. Saturation --> can be saturated if all the binding sites are filled with ligands 3. Affinity --> binds with high strength of interaction to the ligand

Question 36

Describe the role of channel-linked receptors?

Answer 36

- proteins that function as a receptor and ion channel 1. First messengers bind to receptor that opens the ion channel 2. ions cross membrane 3. change in electrical properties of the cell - -> these are fast and can include calcium channels for muscle contractions

Question 37

Describe role of enzyme-linked receptors?

Answer 37

proteins that function as a receptor also have intrinsic enzyme activity - i.e. can phosphorylate a molecule as it crosses

Question 38

Describe role of G-protein linked receptors?

Answer 38

- binds GDP and GTP and has 3 subunits: alpha, beta and gamma - first messenger binds to receptor - alpha subunit binds to guanosine nucleotides and adds a phosphate to it making it active --> GTP. - GTP powers the effector protein somewhere else in the cell

Question 39

What are G-proteins? What are the steps involved in the G-protein cascade?

Answer 39

G proteins: 1. effect ion channels (causing them to open or close) 2. Stimulate G-proteins: activate enzymes 3. Inhibit g-proteins: inhibit enzymes

Question 40

Describe the steps in the cAMP second messenger system

Answer 40

a

Question 41

Describe the steps in the calcium-calmodulin second messenger system

Answer 41

aa

Question 42

What is signal amplification?

Answer 42

ability of small changes in concentration of a chemical messenger to elicit marked responses in target cells

Question 43

What are 3 different types of membrane proteins? Describe each. What are 2 properties of them.

Answer 43

- Phospholipids are amphipathic with polar head groups and non polar tails. - Cholesterol is a steroid that is also amphipathic and maintains cell fluidity (prevents phospholipids from touching each other) - Glycolipids are lipids with a small CHO chain attached (also amphipathic) and form glycocalyx which is involved with identification and interaction between cells - Glycoproteins are proteins with attached carbohydrates that form glycocalyx for cell communication - Distributed unequally and selectively permeable.