Biological membranes

Question 1

Partially permeable meaning?

Answer 1

The membrane can adjust its permeability to only allow certain substances to pass in and out

Question 2

What four mechanisms do molecules move through the membrane?

Answer 2

Diffusion, facilitated diffusion, osmosis, active transport

Question 3

What is osmosis?

Answer 3

Net movement of water molecules from a more dilute solution to a more concentrated solution, across a partially permeable membrane

Question 4

What would the word turgid be used to describe?

Answer 4

When a plant cell contains as much water as possible

Question 5

What is cell lysis?

Answer 5

When an animal cell takes in too much water and it bursts

Question 6

What is active transport?

Answer 6

Movement of ions of molecules through a membrane, against a concentration gradient, with the help of enzymes and energy

Question 7

What is diffusion?

Answer 7

Net movement of ions or molecules down a concentration gradient

Question 8

What is facilitated diffusion?

Answer 8

Passive transport of molecules or ions across a biological membrane via specific transmembrane integral proteins

Question 9

Specific structure of plasma membrane?

Answer 9

Made up of two layers of phospholipids molecules. Their hydrophilic heads (dissolve easily in water) meet the water medium inside and outside the cell, their hydrophobic tails (do not dissolve in water) only present inside the membrane

Question 10

What is embedded between the phospholipid bilayer?

Answer 10

Proteins, intrinsic = completely span, extrinsic = partly embedded

Question 11

Difference between channel and carrier proteins?

Answer 11

Carrier = use ATP to actively move molecules through membrane, Channel = If molecules are too big, forms a tube shape through whole membrane for them to pass

Question 12

What are phagocytes?

Answer 12

WBC whose role is to trap and kill pathogens

Question 13

2 types of phagocytes?

Answer 13

Neutrophils (small and lots), macrophage’ (big and not man y)

Question 14

What is phagocytosis?

Answer 14

When a phagocyte envelopes and engulfs a pathogen and the membrane folds in (now in a phagosome)

Question 15

What does the lysosome do after phagocytosis?

Answer 15

Lysosome fuse with the phagosome forming phagolysosome, releases enzymes into it (lysins), Lysins digest the bacterium

Question 16

Why are B or T cells made?

Answer 16

Produced as part of the specific immune response

Question 17

B plasma cells?

Answer 17

Produce and secrete antibodies while circulating blood

Question 18

B memory cells?

Answer 18

Remain in the body for many years after the initial infection, serve to ‘remember’ the antigen

Question 19

Antigen?

Answer 19

A molecule that is foreign to the body and that stimulates an immune response and production of antibodies

Question 20

What is a glycoprotein?

Answer 20

Proteins with short carbohydrate chain attached

Question 21

What is the role of the carbohydrate chains in glycoproteins?

Answer 21

Form hydrogen bonds with water, stabilising the plasma membrane, also act as receptors in cell signalling

Question 22

What are glycolipids?

Answer 22

Lipids with short carbohydrate chain attached

Question 23

What do glycoproteins and glycolipids form together?

Answer 23

The surface antigens which the immune system identifies as being a cell from its body or a foreign cell

Question 24

What is the main function of cholesterol?

Answer 24

Maintain suitable level of fluidity in plasma membrane

Question 25

What is special about the structure of cholesterol molecules?

Answer 25

Has a hydrophobic and hydrophilic region (can bind to phospholipids and prevent membrane being too fluid

Question 26

What prevents two adjacent fatty acid molecules coming together and crystallising?

Answer 26

The presence of cholesterol molecules between the fatty acid chains, keeping the membrane fluid

Question 27

What affects the membrane structure and permeability?

Answer 27

Temperature, affects both proteins and lipids working

Question 28

What happens to the membrane when temp is increase, in terms of the lipid component?

Answer 28

It becomes more fluid, reducing its effectiveness to polar molecules (some get through barrier)

Question 29

How does temperature affect the cell membrane generally?

Answer 29

Speeds up diffusion of any (polar) molecules getting through, including those not allowed in

Question 30

What critical change happens to cell membranes at about 40 degrees C?

Answer 30

Proteins start to denature, disrupting membrane structure and no longer and effective barrier (this is irreversible)

Question 31

How do multicellular organisms cells work in isolation?

Answer 31

They don’t, they communicate with other cells (near and far)

Question 32

What is cell signalling?

Answer 32

Communication between cells of chemical messenger molecules - produced in one cell and transported to another - only detected by target cells

Question 33

What forms the receptors for cell signalling?

Answer 33

Glycoproteins in the plasma membrane (some evidence that glycolipids might have a role)

Question 34

What do liver cell receptors respond to?

Answer 34

The hormone glucagon, causes them to release glucose from stores of glycogen within cells

Question 35

What is a target cell?

Answer 35

A cell that responds to a particular messengers, due to having complementary receptors

Question 36

What three things might happen as a result of of the messenger molecule binding to a receptor?

Answer 36

Change in receptor may cause release of second messenger inside cell
May result in the opening of a protein channel or closing of one thats open
May activate an enzyme within the cell

Question 37

How can medicinal drugs affect membranes?

Answer 37

Half drugs target specific membrane receptors, can create responses or or block responses