Topic 2 - Genes and Health

Question 1

Lungs

Answer 1

Main role is to deliver gases to and from the bloodstream.

Question 2

What makes a good gas exchange surface?

Answer 2

A high surface area to volume ratio.
A thinner surface.
A steep concentration gradient.

Question 3

Adaptations of the lungs

Answer 3

Large surface area -> alveoli, and lots of capillaries surrounding alveoli.
Concentration gradient -> breathing and blood circulation maintains a high concentration gradient between the alveoli air space and the blood stream. O2 always travel from a high concentration in the alveoli to low concentration in the bloodstream,and CO2 vice versa.
Thickness of diffusion surface -> alveoli and capillaries made of flattened or squamous issue, which relates a short diffusion distance for gaseous exchange.

Question 4

Fick’s Law

Answer 4

Rate of diffusion is proportional to:

surface area of gas exchange surface × difference in concentration
—————————————————————————
thickness of the membrane

A change in one of these can impact the rate of diffusion or gaseous exchange in the lungs.
Proportionality means he diffusion rate will double if:
the surface area or concentration difference doubles
- the diffusion pathway halves

Question 5

Fick’s Law - The lung adaptations

Answer 5

Large surface area -> both alveoli and the capillaries surrounding alveoli.
Concentration gradient -> breathing and blood circulation maintains a high concentration gradient between the alveoli air space and the blood stream. O2 always travel from a high concentration in the alveoli to low concentration in the bloodstream,and CO2 vice versa.
Thickness of diffusion surface -> alveoli and capillaries made of flattened or squamous issue, which relates a short diffusion distance for gaseous exchange.

Question 6

Genetic disorders and proteins

Answer 6

CF is a genetic disorder.
All genetic disorders have an impact on protein structure.
This is due to our DNA being responsible for determining protein structure.

Question 7

Proteins

Answer 7

Used within the body for growth and repair.
Amino acids are monomer units, form a polymer called polypeptide, and combine to form proteins.

Question 8

Amino acids - Structure

Answer 8

H H O
\ | //
N - C - C
/ | \
H H OH

Question 9

Amino acids - Structure

Answer 9

The R group is different for each amino acids.
There are 20 different amino acids, meaning there are 20 different R groups.

Question 10

Formation of a peptide bond

Answer 10

Condensation reaction, with the loss of water.
Peptide bond (covalent) is formed between the carbon of the carboxyl group and the nitrogen of the amine group.

Question 11

Breaking of a peptide bond

Answer 11

Hydrolysis reaction, with the addition of water.
Peptide bond (covalent) is broken.

Question 12

Proteins - Primary structure

Answer 12

A sequence of amino acids are held together by peptide bonds in a polypeptide chain, through a process called polymerisation.
Changing the amino acids may lead to a change in the shape of the protein and could stop it from functioning.

Question 13

Proteins - Secondary structure

Answer 13

Weak hydrogen bonds form between -NH+ and -C=O- groups, which forms a weak hydrogen bond.
This causes the chain to become twisted in either an alpha helix or beta pleated sheet.

Question 14

Proteins - Tertiary structure

Answer 14

Due to interactions between the R groups of amino acids that make up the protein
The protein folds into a 3D shape due to ionic, covalent and hydrophobic interactions.
The sequence of amino acids in the primary structure determines the folding.

The 3D shape is maintained by:
- ionic bonds -> formed between carboxylic and amine group, easily broken.- hydrogen bond -> many but easily broken.
- disulfide bonds -> fairly strong.

Question 15

Proteins - Quaternary structure

Answer 15

There is more than one polypeptide chain that forms the overall protein.

Question 16

Proteins - Tertiary structure - Becoming denatured

Answer 16

By heating.
The heat increases the kinetic energy of the molecule, which makes parts of it vibrate faster.
This means that the non-covalent bonds that hold the protein in its globular shape are broken, causing its complex shape to unravel.

Question 17

Fibrous protein - Collagen

Answer 17

• three long polypeptide chains wrapped around each other that are cross linked to provide strength.
• provides structural support and used in cartilage, ligaments, tendons etc.
• insoluble fibrous protein due to the hydrophobic R groups facing outwards.

Question 18

Globular protein - Haemoglobin

Answer 18

• oxygen-carrying pigment that is found in large quantities in red blood cells.
• has a quaternary structure due to it having four polypeptide chains.
• soluble due to the hydrophilic R groups facing outwards.
• if changes happen to the sequence of amino acids in the subunits, the oxygen-carrying capacity of the blood will decrease. (this is what happens to cause sickle cell anaemia which makes haemoglobin less soluble)

Question 19

Membrane structure - Cell membranes and phospholipids

Answer 19

Cell membranes are made up of phospholipids.
Rule:
- allow lipid soluble substances through
- prevent water soluble substances through
- make membrane flexible and self sealing

Question 20

Phospholipids - Structure

Answer 20

One phosphate (and glycerol) head -> polar, hydrophilic.
Two fatty acid tails -> non-polar, hydrophobic.

Question 21

Cell membrane

Answer 21

Controls the movement substances in and out of cells and organelles.
It is selectively permeable to ions and organic molecules.

Question 22

Fluid Mosaic Model

Answer 22

Multiple components (mosaic).
All components move around constantly, they are fluid.
Made by Singer and Nicholson (1972).
A build on Davison and Danielli’s model.
Bilayer of phospholipids molecules - fluidity.
Proteins floating in the phospholipid bilayer - mosaic appearance.

Question 23

Fluid Mosaic Model

Answer 23

• The freeze fracture images of the cell membranes were evidence against the Davson–Danielli model
• Led to the development of the fluid mosaic model
  •This model suggested that proteins are found within, instead of outside, the phospholipid bilayer.

Question 24

Evidence for the Davson-Danielli model (1970s)

Answer 24

• Clear electron micrographs of membranes -> showed support for the model as it showed a three layered structure.
• It was taken to be the phospholipids bilayer surrounded by two protein layers.

Question 25

Problems with the Davson-Danielli model

Answer 25

- not clear how the proteins in the model would allow the membrane to change shape - no fluidity. - membrane proteins are mainly hydrophobic, so therefore shouldn’t be found where the model positioned them, in the aqueous cytoplasm and extracellular environment. - the proteins would prevent endocytosis and exocytosis from happening.

Question 26

Transport across membranes - Cell membranes, polarity and diffusion

Answer 26

The non-polar, hydrophobic tails of phospholipid molecules in a cell membranes act as a barrier to many substances. Usually, the smaller and less polar a molecule, the easier and quicker it will diffuse across a cell membrane. - small, non-polar molecules, e.g. O2 and CO2, quickly diffuse through the phospholipid bilayer. - small, dipole molecules, e.g. water and urea, diffuse across the phospholipid bilayer, but much slower. Charged ions (particles) can’t diffuse.

Question 27

Exocytosis

Answer 27

Very large, polar or non-polar substances are transported. Requires ATP (energy). e.g. enzymes, antibodies, hormones. Vesicle fuses with cell membrane and the contents are released out of the cell.

Question 28

Endocytosis

Answer 28

Very large, polar or non-polar molecules are transported. Requires ATP (energy). e.g. pathogens. Vesicle formed from the cell membrane and the contents travel into the cell.

Question 29

Facilitated diffusion

Answer 29

Small, polar/charged molecules are transported. Doesn’t require ATP (energy) and goes down the concentration gradient. e.g. Na+, Cl-, glucose. Channel or carrier protein is used. Channel/carrier proteins specific to the substance. High to low concentration.

Question 30

Active transport

Answer 30

Small, polar/charged molecules are transported. Requires ATP (energy), and goes against the concentration gradient. Carrier proteins are used. Carrier proteins specific to the substance. Low to high concentration.

Question 31

Simple diffusion

Answer 31

Small, non-polar molecules are transported. Doesn’t require ATP (energy), and goes down the concentration gradient. e.g. O2, CO2. Net movement of molecules from a high to low concentration until equilibrium is established.

Question 32

Osmosis

Answer 32

Small, dipolar molecules are transported. Doesn’t require ATP (energy), and goes down the concentration gradient. e.g. water (only). Net movement of water through a partially permeable membrane from an area of high concentration to an area of low concentration.

Question 33

CF symptoms and membrane transport

Answer 33

CF ends in more viscous mucus. In a non-CF sufferer, mucus viscosity is able to be regulated: - to make mucus less viscous, water needs to be added by osmosis - to make mucus more viscous, water needs to be removed by osmosis Therefore, the concentration of solutes (in this scenario, chloride ions) determines where water move to by osmosis.

Question 34

CFTR Protein

Answer 34

Cystic Fibrosis Transmembrane Regulator. A channel protein that is either non-functional, partially functional or absent in CF sufferers. It allows for the facilitated diffusion of chloride ions only.

Question 35

A non-CF sufferer is able to change mucus viscosity

Answer 35

CFTR channels open. Chloride ions travel through the channels by facilitated diffusion. Water follows by osmosis, and moves to an area of high solute concentration from an area of low solute concentration. This makes the mucus less viscous. Reverse effect if the CFTR channels close - the solutes will be transported away from the mucus and the water i’ll follow.

Question 36

A CF sufferer can’t change mucus viscosity

Answer 36

CFTR channels are absent or are non-functional. No chloride ions can move through the channels to the mucus by facilitated diffusion. Water moves away from the mucus by osmosis and moves to an area of high solute concentration from an area of low solute concentration. This makes the mucus become excessively dehydrated.

Question 37

Changing enzyme concentration

Answer 37

- rate of reaction increases as more active sites start to be available - more successful enzyme-substrate complexes form - until the substrate becomes the limiting factor

Question 38

Changing substrate concentration

Answer 38

- rate of reaction increases as there is more substrate to it into active sites - more successful enzyme-substrate complexes form - until the enzyme becomes the limiting factor

Question 39

Specificity of enzymes - Intracellular enzymes

Answer 39

Intracellular enzymes are produced in cells by protein synthesis and stay in the cell to perform their function. These enzymes can carry out hydrolysis or catabolic reactions, or polymerisation or anabolic reactions.

Question 40

Specificity of enzymes - Extracellular enzymes

Answer 40

Extracellular enzymes are produced in cells by protein synthesis and are then transported out of the cell by exocytosis to perform their function. These enzymes usually carry out hydrolysis or catabolic reactions.

Question 41

Specificity of enzymes - Catabolic reactions

Answer 41

Metabolic processes that break down large molecules into smaller ones, whilst breaking down ATP and releasing ATP.

Question 42

Specificity of enzymes - Anabolic reactions

Answer 42

Joining smaller molecules together to form larger ones.

Question 43

Structure of DNA

Answer 43

Polymers made up of monomers called (mono)nucleotides. A phosphate group (circle), a penrose sugar (pentagon) and a nitrogen-containing base. The sugar in DNA is deoxyribose. Antiparallel -> two strands of DNA in opposing directions to each other.

Question 44

Structure of RNA

Answer 44

Polymers made up of monomers called (mono)nucleotides. A phosphate group (circle), a penrose sugar (pentagon) and a nitrogen-containing base. The sugar in RNA is ribose sugar.

Question 45

How DNA nucleotides join together, forming a DNA polymer

Answer 45

Condensation reaction between the deoxyribose sugar of one nucleotide and the phosphate group of another. This forms a phosphodiester bond with the loss of water.

Question 46

How RNA nucleotides join together, forming a RNA polymer

Answer 46

Condensation reaction between the ribose sugar of one nucleotide and the phosphate group of another. This forms a phosphodiester bond with the loss of water.

Question 47

Differences between DNA and RNA

Answer 47

DNA is double stranded, the two strands are held together by hydrogen bonds between bases. Whereas, RNA is single stranded. Both have a pentose sugar, but DNA has deoxyribose sugar, and RNA has ribose sugar. Both have (mono)nucleotides joined together by condensation reactions that form phosphodiester bonds. DNA contains the base thymine, whereas RNA has the bae uracil.

Question 48

Complementary base pairing - DNA

Answer 48

Adenine pairs with thymine. Cytosine pairs with guanine. This is called complementary base pairing.

Question 49

Complementary base pairing - RNA

Answer 49

Only temporarily happens during protein synthesis, RNA is single stranded. Because there is no thymine in RNA, adenine pairs with uracil.

Question 50

Mnemonic to help remember which bond goes with which biochemical molecule

Answer 50

Catch -> Carbohydrates Greedy -> Glycosidic Louise -> Lipids Eating -> Ester Poppy’s -> Proteins Pepperoni -> Peptide Dominoes -> DNA/RNA Pizza -> Phosphodiester

Question 51

tRNA cloverleaf shape

Answer 51

Despite it being folded around on itself, tRNA is still single-stranded as all RNA is.