topic 2 - genes and health

Question 1

how is air drawn into the lungs?

Answer 1

via the trachea, due to low pressure in the lungs, created by an increase in the volume of the thorax as the ribs move up and the diaphragm moves down

Question 2

how is air forced out of the lungs?

Answer 2

when the diaphragm muscles and those between the ribs relax, volume decreases, pressure rises, and air is forced out through the trachea

Question 3

what is the function of the alveoli?

Answer 3

they are the site of gas exchange

Question 4

what cells produce mucus in the gas exchange system?

Answer 4

goblet cells

Question 5

how is mucus removed from the gas exchange system?

Answer 5

the cilia that cover the epithelial cells lining the tubes of the gas exchange system sweep mucus along (mucus may contain dust, debris, or microorganisms so needs to be removed)

Question 6

how does cystic fibrosis increase the risk of lung infection?

Answer 6

pathogens could get caught in the mucus, which then cannot be swept away by cilia as mucus is too sticky. there are low levels of oxygen in the mucus, and harmful bacteria can thrive in these anaerobic conditions

Question 7

what are the two types of epithelial cells?

Answer 7

squamous/pavement + columnar

Question 8

what are the features of the gas exchange surface in an alveoli?

Answer 8

• large surface area
• numerous capillaries around
• thin walls to create short diffusion pathways

Question 9

what is fick’s law?

Answer 9

rate of diffusion is directly proportional to (surface area x difference in concentrations) / thickness of the gas exchange surface

Question 10

how does sticky mucus from CF affect gas exchange?

Answer 10

the sticky mucus layer tends to block the bronchioles, preventing movement of air into the alveoli beyond the blockage. this reduces the number of alveoli providing surface area for gas exchange.
some blockages allow gas to pass when the person breathes in but not when they breathe out. this results in over-inflation of the lung tissue, damaging the elasticity of the lungs

Question 11

why is CF mucus so sticky?

Answer 11

the mucus layer on the surface of the epithelial cels is sticky because it contains less water than normal due to abnormal salt (NaCl) and water transport across the cell surface membranes caused by a faulty transport protein channel in the membrane

Question 12

what is the primary structure of a protein?

Answer 12

a sequence of amino acids joined together with peptide bonds to form a polypeptide chain

Question 13

what are the components of an amino acid?

Answer 13

amine group (NH2) carboxylic acid group (COOH), central carbon, hydrogen, and the R group

Question 14

what is the secondary structure of a protein?

Answer 14

the chain of amino acids may twist to form an a-helix
- looks like an extended spring
- hydrogen bonds form between C=O and -NH

amino acid chains may fold back on themselves or link together to form a B-pleated sheet
- hydrogen bonds holding parallel chains in an arrangement
- cumulative effect of many hydrogen bonds makes it quite stable

Question 15

what is the tertiary structure of a protein?

Answer 15

further folding of the polypeptide chain to produce a 3D shape. hydrophilic/hydrophobic interactions, disulphide bonds, hydrogen bonds, and ionic bonds between R groups maintain this structure.

Question 16

how do hydrophilic/hydrophobic interactions determine structure?

Answer 16

• polar R groups attract other polar molecules, and are hydrophilic
• non-polar R groups are hydrophobic
• the hydrophobic R groups are arranged so they face the inside of the protein, excluding water from the centre of the molecule

Question 17

what is quaternary structure of a protein?

Answer 17

only some proteins have a quaternary structure. some proteins can only be functional if they are made up of several polypeptide chains held together. only proteins with more than one polypeptide chain have a quaternary structure

Question 18

what is a conjugated protein?

Answer 18

proteins which have another chemical group associated with their polypeptide chain

Question 19

what is the structure and function of a globular protein?

Answer 19

• compact spherical shape
• soluble
• hydrophilic side chains project from the outside
• important in metabolic reactions
• e.g. enzymes/antibodies
• used as transport proteins

Question 20

what is the structure and function of a fibrous protein?

Answer 20

• long chains
• several polypeptide chains cross-linked for additional strength
• insoluble
• important structural molecules
• e.g. collagen

Question 21

what is the structure of a phospholipid molecule?

Answer 21

two fatty acids, a negatively charged phosphate group, and a glycerol (similar to triglyceride but third fatty acid replaced with phosphate)

Question 22

why is the phosphate molecule polar?

Answer 22

hydrophilic head and hydrophobic tail
- when added to water, phospholipids become arranged with no contact between fatty acid hydrophobic tails and the water

Question 23

what are the features of diffusion across cell membranes?

Answer 23

• down a concentration gradient (from high to low until equilibrium is reached)
• hydrophobic or small uncharged molecules
• through phospholipid bilayer
• passive so no energy required

Question 24

what are the features of facilitated diffusion across cell membranes?

Answer 24

• down a concentration gradient (from high to low until equilibrium is reached)
• hydrophilic molecules or ions
• through channel proteins or via carrier proteins that change shape
• passive so no energy required

Question 25

what are the features of osmosis across cell membranes?

Answer 25

- movement of free water molecules - high to low concentration of free water molecules until equilibrium (low solute concentration to high solute concentration) - through phospholipid bilayer - passive so no energy required

Question 26

what are the features of active transport across cell membranes?

Answer 26

- against a concentration gradient (low to high concentration) - through carrier proteins that change shape - requires energy, supplied by ATP

Question 27

what are the features of exocytosis?

Answer 27

- used for bulk transport of substances out of the cell - vesicles fuse with the cell surface membrane, releasing their contents

Question 28

what are the features of endocytosis?

Answer 28

- used for bulk transport of substances into the cell - vesicles are created from the cell surface membrane, bringing their contents into the cell

Question 29

why do phospholipids form a bilayer?

Answer 29

the two fatty acids are too bulky to fit into the interior of a micelle (spherical cluster of phospholipids)

Question 30

what is the cell surface membrane made up of?

Answer 30

- phospholipid bilayer - proteins - cholesterol - glycoproteins - glycolipids arranged into the fluid mosaic model

Question 31

what is the difference between peripheral and integral proteins in a phospholipid bilayer?

Answer 31

peripheral proteins are loosely attached on the outside surface of the membrane whilst integral proteins are fully embedded within the phospholipids, sometimes spanning both layers

Question 32

what was the mouse an human membrane protein experiment?

Answer 32

- the mouse membrane protein was given a green fluorescent label - the human membrane protein was given a red fluorescent label - the cells were fused, and a light microscope was used to follow where the proteins moved - the coloured labels all remained in their respective halves - after 40 minutes at 37°C, there was complete intermixing of proteins - they intermixed by diffusing through the membranes, showing the components were indeed fluid

Question 33

what determines the fluidity of a cell membrane?

Answer 33

the ratio of unsaturated fatty acids to unsaturated fatty acids. higher ratio = more fluid as the kinks in the hydrocarbon tails prevent them from packing closely together, so more movement is possible. cholesterol sits between the phospholipids, and maintains the fluidity by affecting movement of the phospholipids

Question 34

how do molecules/ions move across membranes?

Answer 34

- diffusion - osmosis - active transport - endocytosis - exocytosis

Question 35

what is diffusion?

Answer 35

the net movement of molecules or ions from a region where they are at a higher concentration to a region of their lower concentration

Question 36

which molecules can diffuse across a membrane easily (via diffusion)?

Answer 36

small uncharged particles can diffuse directly across the cell membrane rapidly, passing between the lipid molecules as they move down the concentration gradient (e.g. oxygen and carbon dioxide). although carbon dioxide is polar, its small size still allows rapid diffusion

Question 37

why is facilitated diffusion necessary?

Answer 37

polar (hydrophilic) molecules and ions larger than carbon dioxide cannot simply diffuse. they are insoluble in lipids (hydrophobic tails of phospholipids provide a barrier), and instead need to cross the membrane with the aid of proteins through water-filled pores within channel proteins

Question 38

how do channel proteins allow facilitated diffusion?

Answer 38

each type of channel protein has a specific shape that permits the passage of only one particular type of ion or molecule

Question 39

what are gated channels and how do they allow facilitated diffusion?

Answer 39

some channel proteins can be opened or closed depending on the presence of a signal (e.g. hormone, change in potential difference), and these are called gated channels

Question 40

hat are carrier proteins?

Answer 40

the ion or molecule binds onto a specific site on the protein. the protein changes shape, and as a result, the ion or molecule crosses the membrane. this can occur in either direction

Question 41

what is osmosis?

Answer 41

the net movement of water molecules from a solution with a lower concentration of solute to a solution with a higher concentration of solute through a partially permeable membrane. osmosis will continue until the solutions on either side are equally concentrated or isotonic

Question 42

how does active transport work?

Answer 42

the substance to be transported across the membrane binds to the carrier protein. one phosphate group is removed from ATP by hydrolysis and ADP forms. he phosphate group then becomes hydrated, releasing a lot of energy as bonds form between the water and the phosphate. this energy changes the shape of the carrier protein, causing the substance to be released