Genes and Health

Question 1

SURFACE AREA AND DIFFUSION

Answer 1

Smaller organisms area able to rely on diffusion to take in nutrients and oxygen and remove waste materials such as carbon dioxide. In unicellular organisms the whole cell surface membrane is the exchange surface - the substances diffuse down the concentration gradient and the gradient is maintained by the cell continuously using the substances and producing waste.

SMALLER ORGANISMS HAVE A MUCH HIGHER SURFACE AREA TO VOLUME RATIO - SO DIFFUSION IS RELIABLE

Question 2

Why can larger organisms not rely on solely diffusion?

Answer 2

Larger organisms have a much smaller surface area to volume ratio.

Larger organisms have a much larger volume than their surface area and more exchange of materials has to take place to meet the organisms metabolic needs (***) - larger organisms more problems absorbing substances because of the size of the organisms surface area compared to its volume.

(***) More chemical reactions happen every second in organisms with a large volume compared to smaller volumed organisms - this means that more oxygen, nutrients and waste products have to be exchanged across the membrane of cells.

Question 3

GAS EXCHANGE SURFACES

Answer 3

The alveoli in lungs have a large surface area for gas exchanges between the air and the blood.

• *NUMEROUS CAPILLARIES AROUND THE ALVEOLI**
• The gas exchange of oxygen and carbon dioxide takes place in the alveoli
• Oxygen from the inhaled air diffuses (from a region of higher concentration to a region of lower concentration) through the walls of the alveoli (epithelial cells) int adjacent capillaries into the red blood cells which carry haemoglobin.
• The oxygen is then carried by the blood to the body tissues
• *THIN ALVEOLI AND CAPILLARY WALLS**
• The alveoli and capillaries have very thin walls which make the distance between the alveolar air and blood in the capillaries much shorter (diffusion is only effective over short distances).

FICKS LAW

SURFACE AREA
The rate of diffusion is directly proportional to the difference in concentration across the gas exchange surface - as the surface area increases the rate of diffusion increases.

CONCENTRATION GRADIENT
The rate of diffusion is directly proportional to the difference in concentration across the gas exchange surface. The greater the concentration gradient the faster the diffusion.

THICKNESS OF GAS EXCHANGE SURFACE
The rate of diffusion is inversely proportional to the thickness of the gas exchange surface - the thicker the surface the slower the rate of diffusion. The gas axing surface is thin as a result of thin alveoli and capillary walls, so the distance between the alveolar air and blood in the capillaries is much shorter.

Question 4

MAGNIFICATION

Answer 4

Is the degree to which the size of an image is larger than the image its self

MAGNIFICATION = size of image / actual size of object

Question 5

RESOLUTION

Answer 5

Is the degree to which it is possible to distinguish between two objects that are very close together.

ACTUAL SIZE = image size / magnification

Question 6

PROTEINS

Answer 6

Proteins are made up of amino acids

Question 7

Amino acids in plants and animals

Answer 7

Plants can make all of the amino acids needed to make a protein but animals can only make some - obtaining the ones they can’t make in their diet. The amino acids that animals obtain in their diet are known as essential amino acids

Question 8

AMINO ACID

Answer 8

Amino acids share the same basic structure, they all contain a carboxylic acid group and an amine group, they also have a hydrogen molecule and a R GROUP (the R GROUP series between different amino acids.

Question 9

CONDENSATION REACTION

Answer 9

Amino acids join together in a condensation reaction (water is removed) to form a DIPEPTIDE with a peptide bond between the two subunits.

Question 10

HYDROLYSIS

Answer 10

Amino acids are separated in a hydrolysis reaction when water is added.

Question 11

REFER TO AMINO ACID SHEET

Answer 11

REFER TO AMINO ACID SHEET

Question 12

PRIMARY STRUCTURE

Answer 12

Amino acids join together in a condensation reaction (water is removed) to form a DIPEPTIDE with a peptide bond between the two subunits. This process may be repeated to produce a polypeptide chain which may contain thousands of amino acids. A protein is made up of one or more of these polypeptide chains and its the sequence of amino acids in the polypeptide chain which is known as the PRIMARY STRUCTURE.

Question 13

SECONDARY STRUCTURE

Answer 13

Interactions between the amino acids in the polypeptide chain cause the chain to twist and fold into a 3D shape - lengths of the chain may first coil into alpha helices or come together in beta pleated sheets.

Within the alpha helix, hydrogen bonds from between the slightly negative C=O of the carboxylic acid and the slightly positive -NH of the amine group of different amino acids that lie above and below each other which stabilises the shape.

Amino acids may fold back on themselves, or several lengths of the chain, which may link up together with hydrogen bonds holding the parallel chains in an arrangement known as a BETA PLEATED SHEET. Each hydrogen bond is week but the cumulative effect of many hydrogen bonds makes the structure stable.

Question 14

TERTIAY AND QUATERNARY STRUCTURE

Answer 14

A polypeptide chain often bends and folds further to produce a precise 3D shape - chemical bonds and hydrophobic interactions between R groups maintain this final tertiary structure of a protein.

If the 3D structure is functional then the molecule is able to perform its specific function and is now described as a PROTEIN

Some amino acids may 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; single chained proteins stop at the tertiary structure.

Question 15

CELL MEMBRANE STRUCTURE

Answer 15

The cell membrane is made up of a phospholipid bilayer. In a phospholipid there are only two fatty acids; a negatively charged phosphate group replaces the third fatty acid found in a triglyceride lipid model (3 fatty acids and glycerol).

Question 16

PHOSPHOLIPID MOLECULE

Answer 16

A phospholipid molecule is made of a hydrophilic head and a hydrophobic tail (fats). The phosphate head of a molecule is polar (one ned is slightly positive and one end is slightly negative), this makes the phosphate head attract to other molecules like water, the fatty acid tails are non-polar and therefore hydrophobic.
When added to water the phospholipids become arranged so that there is no contact with the hydrophobic tails and the water. They may form a layer on the surface with their hydrophobic tails directed out of the water.

Question 17

FLUID MOSAIC MODEL

Answer 17

The cell surface membrane is not simply made up of a phospholipid bilayer; it also includes proteins, cholesterol, glycoproteins (protein molecules with polysaccharides attached) and glycolipids (lipid molecules with polysaccharides attached).

Its thought that some of the proteins are fixed within the membrane but others aren’t and can move around the fluid phospholipid bilayer (FLUID MOSAIC MODEL)

Question 18

HOW DO SUBSTACES MOVE THROUGH MEMBRANES?

Answer 18

For a cell to function properly it has to be able to control transport across its surface; molecules and ions can move across membranes by; diffusion, osmosis, active transport, exocytosis and endocytosis

DIFFUSION
Diffusion is the net movement of molecules/ions from a region of higher concentration to lower concentration. Particles are constantly moving randomly in all different directions but where theres a high concentration of particles there is an increase probability that the particles move away towards the area of lower concentration - resulting in the overall net movement.
Diffusion will continue until equilibrium when all the particles of a substance are evenly spread throughout the whole volume.

FACILITATED DIFFUSION
Hydrophilic molecules can’t diffuse through the boiler because they’re insoluble lipids (water and fats don’t mix), the hydrophobic tails of the phospholipids provide an impenetrable barrier, they cross the membrane with proteins (facilitated diffusion).
Diffusion, facilitated diffusion and non-facilitated diffusion can also be called ‘PASSIVE TRANSPORT’ because no metabolic energy is required for the process - its driven by the concentration gradient.

OSMOSIS
Osmosis is 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

ACTIVE TRANSPORT
If substances need to be moved across a concentration gradient then energy is required - specific carrier proteins are needed.
The energy is supplied by the energy transfer molecule ATP (adenosine triphosphate) - ATP is formed during respiration (the breakdown of energy storage molecules).
The substance that needs to be transported across the membrane binds to the carrier protein, one phosphate group is removed from ATP by hydrolysis and ADP (adenosine diphosphate) forms.
A small amount of energy is required to break down the bod holding the phosphate in the ATP - once removed, the phosphate group becomes hydrated and a lot of energy is released as bonds form between water and phosphate. The energy from the ATP changes the shape of the carrier protein, causing the substance to be released on the other side of the membrane and moving it against the concentration gradient.

EXOCYTOSIS and ENDOCYTOSIS

• Sometimes very large molecules /particles need to be transported across cell surface membranes - the bulk transport is achieved by exocytosis and endocytosis.
• Exocytosis is the release of substances from the cell, vesicles (small membrane bound sacs containing the substance) fuse with the cell membrane and the contents are released
• Endocytosis is the reverse process, substances are taken into the cell by the creation of a vesicle from the cell surface membrane. Part of the cell membrane engulfs the solid or liquid material to be transported.

Question 19

CONCENTRATION GRADIENT

Answer 19

The difference in concentration between two areas