Chapter 5 Cell membranes and Signalling

Question 1

What determines the structure and function of the cell membrane

Answer 1

Its contents - lipids, proteins and carbohydrates

Lipid molecules are phospholipids, which may vary in length, degree of saturation and kinds of polar groups present

Question 2

What is the role of cholesterol it the cell membrane?

Answer 2

their hydroxyl groups interact with phospholipid head and modulate membrane fluidity

Question 3

What factors affect membrane fluidity

Answer 3

Lipid composition - short unsaturated chains increase fluidity
Temperature - fluidity decreases with temperature

Question 4

What are the two types of proteins present in the cell membrane

Answer 4

Peripheral membrane protein - lack hydrophobic group, not embedded in bilayer
Integral membrane protein - have hydrophobic lipid component (may have domains that function differently on inner and outer sides of membrane)

Question 5

What factors restrict the movement of membrane proteins

Answer 5

Intracellular proteins and cytoskeleton attachments

Question 6

What is the role of carbohydrates in the cell membare

Answer 6

Communication and cell adherence via carbohydrate + protein interactions

Question 7

What are the three main types of proteins in thee cell membrne

Answer 7

Glycolipids - carbohydrate + Lipid
Glycoprotein - oligosaccharide and protein
Proteoglycan - Protein + longer carbohydrate

Question 8

What are the differences between passive and active transport?

Answer 8

passive - does not require energy. Substance move down concentration gradient
Active- requires metabolic energy. Substances move against concentration gradient.

Question 9

What are the 2 types of passive transport?

Answer 9

Simple diffusion through phospholipid bilayer

Facilitated diffusion through channel proteins or aided by carrier proteisn

Question 10

What is diffusion?

Answer 10

process of random movement towards equilibrium. Net movement down a concentration gradient

Question 11

What factors affect the speed of diffusion

Answer 11

Diameter of molecules
Temperature
Concentration gradient

Question 12

What is osmosis and osmotic pressure

Answer 12

Osmosis - diffusion of water through special channels

Osmotic pressure - pressure that when applied to solution prevents water diffusion across a membrane

Question 13

What molecules can pass via simple diffusion

Answer 13

O2, CO2, small, nonpolar, lipid soluble molecules

Question 14

What is a hypertonic solution

Answer 14

Solution has higher solute concentration

Question 15

What is turgor pressure

Answer 15

Internal pressure against a cell wall

Question 16

What are the structures that allow faciliated diffusion?

Answer 16

Channel proteins (less specific)
Ion channels (Specific ions)
Aquaporins (Water with concentration gradient)

Question 17

What is the role of carrier proteins

Answer 17

speed up diffusion through channel proteins by binding to substances
Can become saturation, so rate of diffusion reaches maximum

Question 18

Ion channels are mostly gates. What stimuli commonly activate?

Answer 18

Voltage gated

ligand gated

Question 19

What are the 2 types of active transport?

Answer 19

Primary active - involves direct hydrolysis of ATP for energy
Secondary active - uses energy from ion concentration gradient or electrical gradient

Question 20

How do cell smove large macromolecules in and out?

Answer 20

Exocytosis and Endocytosis

Question 21

How does exocytosis work?

Answer 21

Vesicle membrane fuses with the cell membrane and contents are released into the environment

Question 22

How does endocytosis work?

Answer 22

Cell membrane invaginates or folds around particles to form a vesicle that then separates from the cell membrane
- depends on receptors (integral proteins) that bind to ligand

Question 23

What is phagocytosis?

Answer 23

cellular eating
Process of specialised cell engulfing a larger particle or another cell - forms vesicle that then fuses with lysosome for digestion

Question 24

What is pinocytosis

Answer 24

cellular drinking

Smaller vesicles than in phagocytosis bring in fluids and dissolve substances

Question 25

What does receptor endocytosis do?

Answer 25

bring specific large molecules into cell via specific receptors - plays role in cell signalling and allows cells to control internal processes

Question 26

what are the receptors for endocytosis on the cell membrane called?

Answer 26

coated pits - when binds to ligand coated pit invaginates to form coated vesicle (coated with clatharin which stabilizes the vesicle, which is lost when the vesicle is inside the cell)

Question 27

What happens to receptors for endocytosis

Answer 27

recycled to cell membrane or degraded in a lysosome - controls abundance on the cell

Question 28

Cells can process external signals from their environment including:

Answer 28

heat, light and chemicals (ligands) | - Must have a receptor for the signal to respond

Question 29

What happens when a cell's receptor is acrivated

Answer 29

Signal transduction pathway is initiated

Question 30

What are the types of signals that occur in animal cells?

Answer 30

Autrocrine - affect same cells that release them Paracrine - diffuse to and affect nearby cells Justacrine - requrie direct contact between signalling and responing cells Hormones- travel to distant cells

Question 31

What are the components of a signal transduction pathway

Answer 31

signal + receptor + response often include allosteric regulation

Question 32

What is allostreric regulation

Answer 32

Proteins change shape as a result of a molecule binding at a site other than the active site

Question 33

How are receptors classified?

Answer 33

Location - Intracellular (small ligands or nonpular and can diffuse across membrane) - Membrane (large or polar ligands)

Question 34

What type of bond is ligand-receptor bonding and why is this important

Answer 34

noncovalent and reversible | Allows for signal to stop

Question 35

How do Ion channel receptors work

Answer 35

Are ligand gated - change shape when ligand binds

Question 36

Describe the activation of protein kinase receptors

Answer 36

Ligand binds, exposes or activated cytoplasmic domain that has protein kinase acrivity - adds phosphate group to proteins

Question 37

Describe the activation of G protein-linked receptors

Answer 37

ligand binds, exposes site on cytoplasmic side that binds to mobile membrane protein (G protein) - Activated receptor exchanges GDP nucleotide bound to G protein for higher energy GTP protein - Activated protein activated effector protein à signal amplification

Question 38

What parts make up G proteins

Answer 38

receptor, effector protein and GDP and GTP (are used for energy transfer)

Question 39

Describe the process of signal transduction

Answer 39

Signal -> activated receptor -> cellular response: mediated by singal transduction pathway -> signal initiates protein interactions -> amplifies and distrubutes signal -> changes cell function

Question 40

What are the different cell responses to signals

Answer 40

Ion channels open Altering gene expression Enzyme activity alteration Same signal can have different responses in different cells

Question 41

What is the role of secontary messengers for signals

Answer 41

regulate enzymes by non-covalently binding | Distribute the signal further (allow the cell to respond to single event with many events inside the cell)

Question 42

How do signal transduction pathways affect the original signal?

Answer 42

Amplify it at each step

Question 43

How is the signal transduction stopped?

Answer 43

End the signal after the cell response - transducer converted into precursor by enzymes - Balance between regulating and signalling enzymes determines the cell's response

Question 44

How do cells alter enzyme balance

Answer 44

Synthesis and breakdown of enzymes | activation and inhibition of enzymes