1&2. Proteins and Cell Membranes

Question 1

What is the SA:V ratio on a small organism?

Answer 1

Large compared to that of larger organsims

Question 2

Why do most large organisms have a respiratory system?

Answer 2

They have a small SA:V ratio so cannot meet the requirements through diffusion over the surface alone

Question 3

How can the rate of diffusion be increased?

Answer 3

Large surface area, steep conc gradient, thin exchange surface/short diffusion pathway

Question 4

How is the mammalian lung adapted for rapid gas exchange?

Answer 4

Alveoli have a large SA, steep concentration gradient which is maintained by ventilation, thin walls and capillaries that run close to the alveoli create a short diffusion pathway so it is rapid

Question 5

Describe the structure of an amino acid.

Answer 5

Amine group, central carbon with H and R group, carboxyl group

Question 6

What type of bond holds amino acids together?

Answer 6

Peptide

Question 7

How is the primary structure of a protein formed?

Answer 7

Individual amino acids join in condensation reactions and are held together by peptide bonds.
Also known as a polypeptide chain

Question 8

How is the secondary structure of a protein formed and what are its features?

Answer 8

Alpha helices form as a result of the chain twisting and are held in place by hydrogen bonds formed between amine and carboxyl group.
Beta-Pleated sheets form as a result of several chains linking together with hydrogen bonds stabilising the parallel arrangement.

Question 9

How is the tertiary structure formed?

Answer 9

Interactions between R groups fold the polypeptide chain into a unique 3D shape

Question 10

What type of bonds maintain the tertiary structure?

Answer 10

Ionic, hydrogen and disulfide

Question 11

How is the quaternary structure formed?

Answer 11

When several polypeptide chains link together.

Question 12

What is a globular protein?

Answer 12

The polypeptide chain is folded into a compact spherical shape. Hydrophilic side chains on outside make them soluble.
Enzymes are an example

Question 13

What is a fibrous protein?

Answer 13

Several polypeptide chain twisted together like a rope and held together by hydrogen bonds and cross links.
They are insoluble
Collagen is an example

Question 14

What is the purpose of staggered cross links in a fibrous protein?

Answer 14

They hold each strand together and the staggering prevents any weak points along the strand.

Question 15

What is a cell membrane primarily made up of?

Answer 15

A phospholipid bilayer

Question 16

Why do phospholipids arrange in the way that they do in water?

Answer 16

Phosphate head is hydrophillic as it is slightly positive so attracted to other polar molecules i.e water
Fatty acid tails are hydrophobic as they are slightly negative

Question 17

Why does the bilayer arrange the way that it does?

Answer 17

If all the fatty acids tails turned towards the inside there would be very little space within the cell

Question 18

What other components make up the phospholipid bilayer?

Answer 18

cholesterol, glycoprotein, glycolipid, proteins that can be embedded or peripheral

Question 19

Why is the bilayer described as ‘fluid’?

Answer 19

The phospholipids are constantly moving and proteins can move round within it

Question 20

What is a glycoprotein?

Answer 20

A protein with a polysaccharide chain

Question 21

What is a glycolipid?

Answer 21

A lipid with a polysaccharide chain

Question 22

What effect does cholesterol have on the membrane?

Answer 22

Effects fluidity as it forms bonds with phospholipids making the bilayer more rigid.
More cholesterol=less fluidity

Question 23

Describe the features of diffusion.

Answer 23

High to low conc until equilibrium
Hydrophobic or small uncharged molecules move through bilayer
passive process

Question 24

Describe the features of facilitated diffusion.

Answer 24

High to low conc until equilibrium
Hydrophillic molecules or ions through channel proteins or carrier proteins
passive process

Question 25

Describe the features of osmosis

Answer 25

Movement of water molecules from a high to low conc of free water molecules/ movement of water molecules from low solute conc to high solute conc Through bilayer or channel proteins passive process

Question 26

Describe the features of active transport.

Answer 26

low to high conc through carrier proteins requiring energy from ATP active process

Question 27

Describe the features of exocytosis.

Answer 27

Bulk transport of substances out of the cell | Vesicles fuse with cell surface membrane and release their contents

Question 28

Describe the features of endocytosis.

Answer 28

Bulk transport of substances into the cell | Vesicles are created from cell surface membrane and bring their contents into the cell

Question 29

How is excess water removed from the mucus?

Answer 29

1. Na+ actively pumped across basal membrane into tissue fluid 2. Na+ diffuses through sodium channel in apical membrane due to change in conc 3. Cl- diffuses down electrochemical gradient into the tissue fluid 4. High salt conc in tissue fluid drawn water out of cells 5. Water drawn out of mucus due to change in conc gradient (goes from high to low)

Question 30

How is water added to the mucus?

Answer 30

1. Cl- actively pumped across basal membrane into the cell 2. Cl- diffuses through open CFTR channel in apical membrane into the mucus 3. Na+ diffuses down electrochemical gradient into the mucus 4. High salt conc in mucus draws water out of cell into mucus 5. Water taken into the cell by osmosis from the tissue fluid

Question 31

What happens in water content regulation in a person with CF?

Answer 31

1. CFTR channel not functional or absent 2. Na+ channel permanently open 3. The electrochemical gradient cannot be reversed as Cl- always moves toward tissue fluid and Na+ into the cell 4. Water is constantly removed from the mucus

Question 32

What effect does CF have on the digestive system?

Answer 32

CFTR channel is absent or not functioning so viscous mucus blocks the pancreatic duct so fewer enzymes are secreted into the small intestine. Food is not properly digested which can lead to weight loss

Question 33

What effect does CF have on the male reproductive system?

Answer 33

Vas deferens can be missing or blocked by viscous mucus, so fewer/no sperm are released which causes infertility

Question 34

What effect does CF have on the female reproductive system?

Answer 34

A viscous mucus plug builds up in the cervix preventing sperm from swimming through to fertilise an egg in the oviduct.

Question 35

What effect doe CF have on the respiratory system?

Answer 35

Viscous mucus can not be wafted away by cilia so builds up. Bacteria are therefore not removed and so can cause lung infections as conditions are anaerobic as oxygen cannot easily diffuse through the mucus layer