CellsCompare the structure of generalised prokaryotic and eukaryotic animal cells.

Prokaryotic cells do not have large or complex organelles; eukaryotic cells have more membrane-bound organelles such as mitochondria, rER and golgi apparatuses.

Prokaryotes do not have a nucleus but a nucleoid containing circular uncoiled DNA;Eukaryotes have a nucleus with a double nuclear membrane and contain uncoiled chromosomes called chromatin.

Prokaryotes have a cell wall; eukaryotes do not. Both prokaryotes and eukaryotes have plasma membrane and cytoplasm. Both prokaryotes and eukaryotes have ribosomes; prokaryotic ribosomes are

much smaller and eukaryotes have ribosomes attached to the rER. Prokaryotic flagella are embedded in the cell wall and are solid and inflexible;

eukaryotic flagella are not.

Distinguish the differences between animal and plant cells.

Plants have cellulose cell wall outside plasma membranewhich provides support and maintains shape of cell, prevents excess water entering by osmosis;Animal cells do not have cell walls or rigid shape to which allow movements and transport of solids in and out of cell.

Plants have large permanent vacuole which maintain turgor pressure and absorb mineral ions quickly for plant growth; Animals have vesicles which allow endo/exocytosis, less mass without vacuole and more movement.

Plants cells have chloroplasts which are green and synthesise starch; animals do not starch synthesise or store starch and must absorb food.

Identify function and structures of organelles in a eukaryotic animal cell.Nucleus

Has double membrane with pores called nuclear envelope Contains chromatin (uncoiled dna)

o Store dna for replication and transcriptionRough Endoplasmic Reticulum

Flattened membrane sacs called cisternae Ribosomes are attached to exterior cisternae

o Synthesise protein to pass into cisternae and carried to golgi by exocytosis in vesicles

Golgi apparatus Fllatened curved membrane called cisternae No ribosomes with vesicles

Smooth Endoplasmic ReticulumFree ribosomes

Site of protein synthesis

Transcribed mRNA attaches to small subunit of ribosome, tRNA carrying corresponding anticodons and amino acids bind to large subunit and form polypeptides and glycosidic bonds.

Lysosomes Digestive hydrolytic enzymes to break down molecules or dead organic material

for cell usesSpindle fibres

extracellular component to protect and maintain cell shape as cell grows during interphase

Forms MTOC during mitosis and meiosis, attaches to centromeres of chromatids and pull pairs apart, cause genetic variations

Plasma membrane phospholipids bilayer with hydrophobic non-polar tails facing inwards, and

hydrophilic polar heads facing outwards to cytoplasm and aqueous fluid. Barrier against large or charged molecules prevent diffusion which can disturb

concentration in cytoplasm control substances in and out of cell maintain cell shape and binds organelles within cell

Mitochondria double membrane matrix respiration produce ATP energy source for chemical reactions

Cytoplasm fluid in which metabolic reactions occur

Explain how the surface area to volume ratio influences cell sizes.

Smaller cells have larger SA to volume ratio than large cells. As cell size increases, the surface area to volume ratio decreases. Greater surface area allows faster rate of exchange of nutrients needed and

oxygen by diffusion. If ratio too small then substances will not enter cell quick enough and cell

overheats. If ratio too large then cell loses heat quickly.

Outline the advantages of using light microscopes in comparison with electron microscopes.

easy to prepare a sample for living material can be viewed / living processes (e.g. cytoplasmic streaming) can

be seen colour images can be seen relatively portable relatively cheap larger field of view

Membranes List the functions of the proteins on the plasma membrane.

Hormone binding sites Cell adhesion Communication between cells Channels for passive transport Pumps for active transport

Describe and explain the structure of a plasma membrane in a fluid mosaic model. Glycoproteins

composed of carbohydrate chain (short polysaccharides) attached to proteinso act as energy sourceo act as hormone binding sites, such as insulin receptors

Peripheral proteins proteins temporarily attached to an integral protein in the interior of the membraneo act as immobilised enzymes with the active site on the outside o catalyse chemical reactions in the cytoplasm

Phospholipid bilayercomposed of phospholipids with hydrophobic tails facing inward and hydrophilic heads facing outward to the aquaeous extracellular fluid and cytoplasmo hydrophilic heads of phospholipids form hydrogen bonds with aquaeous

solution which helps stabilise the membraneo hydrophobic tails create barrier preventing diffusion of charged or large

molecules but allow gases such as oxygen and carbon dioxide to diffuse across and water to osmose through

Integral transport proteinsproteins permanently embedded in the plasma membraneo specific protein pumps for active transporto specific channels for ions (eg Na, K) or large molecules (eg glucose)o catalyse chemical reactions in cytoplasm

Glycolipidslipids attached with carbohydrate chainso provides energyo act as markers for glycoproteinso stabilise membrane

Cholesterolfatty acids linked togethero stabilise and strengthen membraneo permanently attached to membraneo regulate mobility and rigidity of membrane

List the functions of the plasma membrane Maintain internal pH of cell

Maintain cell shape Regulate the movement of substances in and out of the cell Isolate the two aqueous solutions

Explain how the structure and properties of phospholipids help to maintain the structure of cell membranes.

The plasma membrane is formed from a bilayer of phospholipids. Phospholipids have a hydrophilic head and hydrophobic tail. Hydrophilic heads face outward to the cytoplasm and exterior of the cell Hydrophobic tails face inwards to each other The hydrophilic heads are polar as they compose of carboxylic head and

hydrophobic tails are non-polar as they are formed from two fatty acid chains. Hydrophilic heads form hydrogen bonds with water in cytoplasm and

extracellular fluid which stabilises the membrane The tails maintain a hydrophobic environment to prevent diffusion of charged

molecules into the cell which would change the pH of the interior. Phospholipids are held together by hydrophobic interactions of the tails which

allow the membrane to be flexible and the cell mobile. Double bonded unsaturated hydrocarbon tail in the fatty acid make the membrane

more flexible.

Explain the transport of substances across the plasma membrane in the process of endocytosis and exocytosis.

Endocytosis and exocytosis are processes in which large or polar molecules are transported across the cell membrane by means of vesicles without entering the cytoplasm.

There are three types of endocytosis: phagocytosis, pinocytosis and receptor-mediated endocytosis.

Phagocytosis is when vesicles transport large solid molecules such as proteins, bacteria or fragment of organic matter. Unicellular organisms use phagocytosis to ingest foods.

Pinocytosis is when vesicles transport liquids across the cell membrane, for example when unicellular organism remove excess water from the cell.

Receptor-mediated endocytosis is when specific molecules are taken into the cell.

In phagocytosis1. The plasma membrane extends and invaginates around the substance to be

transported, forming a pocket.2. The pocket deepens and the pseudopodia of the membrane projections fuse,

enclosing the substance in a vesicle, called a phagosome.3. The vesicle moves inside the cytoplasm of the cell, carrying the substance in a

droplet of external fluid to the appropriate organelle.4. In unicellular organisms and human macrophages, the phagosome is fused with

the membrane of a lysosome.

5. Once fused, the contents of the phagosome mix with the digestive enzymes within the lysosome.

6. The enzymes break down the ingested organic material into smaller molecules and are transported to the cytosol to be used.

In receptor-mediated endocytosis1. An example of receptor-mediated endocytosis is the transport of cholesterol Low

Density Lipoproteins.2. LDL receptors on the surface of the membrane specific to the LDL molecules

collect the LDL.3. LDL molecules bind to the receptors and the tails of the receptors are coated by

adaptin and clathrin which cause the membrane to invaginate.4. The membrane buds off the membrane forming a vesicle, carrying the LDL

molecules and the bound LDL receptors to the endosome, where the ingested materials are transported to the lysosome and the vesicle return to the membrane.

In pinocytosis1. Small convex pits form on the plasma membrane surface to collect fluid.2. The convex pits deepen and form small pinocytic vesicles, trapping the fluid and

dissolved substances.3. The vesicles pinch off from the plasma membrane and bring the fluid contents

into the cell.4. Eukaryotic cells have a constant stream of pinocytic vesicles budding off the

plasma membrane. To prevent the depletion of the membrane, the area of the membrane is replenished by exocytosis.

In exocytosis1. Vesicles from inside the cell containing substances to be expelled migrates to the

plasma membrane.2. Vesicle attach to snare of the membrane.3. The vesicle fuses with the plasma membrane, adding to the surface area of the

membrane and releasing its contents into the environment.

Explain how vesicles are used in cells, including the way in which they form and are reabsorbed.

A vesicle is a small spherical sac of membrane with a droplet of fluid inside. Vesicles are formed at the inner surface of the plasma membrane of the cell. The formation of vesicles require the energy of ATP. Vesicles are used to transport material such as protein or bacteria inside and out of

the cell, in endocytosis and exocytosis. Macrophages in blood engulf bacteria in phagocytosis to prevent infections. In secretory cells, proteins syntehsised by ribosomes on the rER are stored in the

cisternae, where vesicles bud off to carry the protein to the golgi apparatus. The vesicles carrying the processed protein are released from the Golgi and fuse

with the plasma membrane, releasing the protein into the extracellular fluid.

Cell divisions

Define mitosis, meiosis and fertilisation.Meiosis is the process by which hereditary information is halved during the production of gametes.Mitosis is the division of a eukaryotic nucleus into two genetically identical nuclei.Fertilisation is the union of sex cells from two different parents.

Distinguish the difference between the division of prokaryotic and eukaryotic cells.Prokaryotic cells reproduce by binary fission in which single circular chromosomes are replicated whereas eukaryotic cells reproduce via mitosis or meiosis.

Define the central dogma.The central dogma states that genetic information must be transferred from parents to offspring and that genes must be inherited.

Describe the stages in the cell cycleThe cell cycle is the sequence of events which a cell undergoes during its lifetime.

During interphase the cell grows and prepares for division. In G1 (Growth One) phase of interphase, metabolic changes such as protein

synthesis occur in the cell and the cell grows. During S (Synthesis) phase of interphase, number of mitochondria or chloroplasts

increase and DNA synthesis occur, replicating chromosomes into two chromatids. In G2 (Growth Two) the cell double checks genes for errors in need of repair.

Damaged dna are destroyed in apoptosis.Cell Division then occurs when the organism grows or repairs. Cell then undergoes mitosis and split into two genetically identical cells by

cytokenesis.

Describe the process of mitosis. Mitosis is the division of a eukaryotic cell into two genetically identical nuclei. Before mitosis takes place the chromosomes are replicated to produce two

identical DNA molecules called sister chromatids.1. Prophase

The chromosomes contract and become shorter by supercoiling. Condensed chromosomes become visible.

Microtubules grow from poles of the cell to from MTOC (microtubule organising centre) to the chromosomes.

Microtubules form spindle and nuclear membrane disintegrates.2. Metaphase

Spindle microtubule fibres attach to centromeres of the chromosomes at different poles.

Chromosomes line up at the cell equator.3. Anaphase

Pairs of sister chromatids separate at the centromere and are pulled to opposite poles as spindle fibres shorten.

4. Telophase Nuclear membranes reform around chromatids. Chromatids uncoil into chromosomes and are replicated. Two diploid nuclei are formed. Cleavage furrow forms in the cytoplasm. Cytokenesis takes place. Cells divide and two genetically identical cells are

generated. The two daughter cells re-enter interphase.

Meiosis

Describe the behaviour of chromosomes during process of meiosis.Meiosis is achieved by halving the number of chromosomes.Prophase

Chromosomes are replicated consisting of two identical chromatids. Homologous chromosomes pair up in synapsis. Homologous chromosomes exchange genetic material with each other in chiasma. Spindle fibres from MTOC to poles of cell Spindle fibres attach to centromere of chromatids Nuclear membrane disintegrates.

Metaphase

GeneticsDefine diploid, haploid and homologous.A diploid nucleus has two chromosomes.A haploid nucleus has only one chromosome.A homologous pair of chromosomes are where the chromosomes contain identical genetic information carrying the same loci genetic traits.

Distinguish between chromosomes and chromatids.A chromosome consists of a single dna molecule whereas sister chromatids are the two identical dna molecules.

Distinguish the difference between autosomes and sex chromosomes.Sex chromosomes called allosomes determine gender whereas autosomes do not.

Define the terms gene and allele and explain how they differ.A gene is the genetic information which determine the characteristics of an organism where an allele is

Explain how meiosis and fertilization can give rise to genetic variety.

Describe how sexual reproduction promotes genetic variation within a species. During prophase in meiosis homologous chromosomes swap genetic information

in chiasmata, creating variance in genes. Alleles are segregated in meiosis which give a greater number of combinations of

genes. The alignment of chromosomes during metaphase I in meiosis is random and

independent of other homologous pairs. Fertilisation combines variety of genes from male and female which produce

offspring with genes from both parents. Mutations may occur during meiosis which could produce new genotypes. Humans have 21 pairs of chromosomes with 23 chromosomes in each haploid

cell, resulting in 8 million possible combinations of genes. Alleles come from two different parents.

Define the term sex linkage.Sex Linkage is a gene which determines different phenotypes in males and females.

Explain Mendel’s 3:1 ratio. Mendel created hybrids of dominant and recessive plants. The hybrids were fertilized with another hybrid and it was found that the ratio for

the dominant characteristic to recessive characteristic was 3 to 1. This shows that when gametes fuse the alleles have already been separated so that

characteristics are not blended.Explain the relationship between Mendel’s law of segregation and meiosis.

law of segregation states that one half of the alleles enter one gamete and the other half enter the other gamete;

meiosis reduces the chromosome number by half / diploid to haploid; homologues carrying alleles separate (in anaphase I); end result is four cells, half with one allele/homologue and the other half

with the other allele;

Outline the differences between the behaviour of the chromosomes in mitosis and meiosis.

In mitosis the chromosomes line up at the cell equator whereas in meiosis the homozygous chromosomes line up at either side of the equator.

In meiosis chromosomes swap genetic information during chiasmata in prophase whereas in mitosis chromosomes do not exchange genes.

In meiosis the homozygous chromosomes line up in pairs whereas in mitosis they do not.

There are two divisions of chromosomes in meiosis but only one in mitosis. After telophase in meiosis chromosomes do not undergo S phase or replicate

whereas in mitosis the chromosomes return to interphase S phase.

Define locus and genomeLocus is the specific position on one homologous chromosome of a gene.Genome is the whole of the genetic information of an organism.

Digestion

Describe the role of enzymes in the process of digestion of proteins, carbohydrates and lipids in humans.

Enzymes are biological catalysts which speed up chemical reactions Enzyme actives sites are specifically complementary to shape of substrates Rate of reaction highest at optimum pH, optimum temperature, optimum

concentration of substrates and enzymes Substrates bind to active site, lowers activation energy Enzymes such as protease hydrolyses proteins into polypeptides, amylase digest

polysaccharides into disaccharides and lipase with lipids into glycerol and fatty acids.

Proteins, carbohydrates and lipids are broken down, hydrolysed into smaller polypeptides

Some amino acids are essential for the body but cannot be synthesised and must be ingested through food. These proteins are digested by the enzymes to be assimilated in the liver for the body to use.

Explain the process of digestion, absorption and assimilation.1. Food enter mouth, salivary gland secretes saliva which contains amylase.

At optimum pH 7, salivary amylase breaks down starch into maltose. Large pieces of food are chewed by teeth into smaller lumps and passes through the

oesophagus into the stomach.2. Stomach walls are glandular and gastric glands secretes protease (pepsin), mucus and hydrochloric acid.

Acidic conditions of pH 2 optimise rate of hydrolysis and kills bacteria, denatures proteins and protease breaks polypeptides into small amino acids.

Stomach walls are elastic which stretch to store food for long periods of digestion. Stomach muscles contract and squeeze food rhythmically to break into smaller

lumps for larger surface area for digestion.Absorption3. Food passes into small intestine for absorption.

Small intestine is lined with finger-like projections of villi which are folded to increase surface area for digestion and absorption.

Villi have layer of microvilli which increases surface area of absorption. Villi are lined with dense network of capillaries which transport absorbed

molecules quickly. Food molecules can diffuse quickly through single layer of epithelial cells on the

villi into capillaries. Small intestine is moist with mucus secreted from goblet cells in the villi and

makes absorption easier. Bile is released from gallbladder into small intestine through the common bile

duct. Pancreatic juices secreted from pancreas through the pancreatic duct contain

protease, lipase and amylase, wall of small intestine secrete nuclease which digest dna.

Lipase hydrolyses lipids into glycerol and fatty acids. Bile emulsifies fat droplets into small micelles, increases surface area for lipase to

digest and absorbed by villi into lacteal as lipoproteins where they are transported via exocytosis into the bloodstream.

Muscles around lacteal contract to make villi shorter and squeeze fluid along. Long length of small intestine allow time for digestion to take place slowly Peyer’s patches contain lymphocytes which detect pathogens and produce

antibodies to defend against them.4. Remainder of undigested matter passes into large intestine, where water and mineral

ions are extracted. Faeces are stored in the large intestine until they are excreted through the rectum

and anus.Assimilation1. Blood carrying absorbed molecules are perfused to the liver. 2. Harmful substances are detoxified and phagocytic cells engulf bacteria.3. Blood is transported to lungs and heart to be pumped to rest of body.

Transport SystemOutline the events that occur within the heart, which cause blood to move around the body.

1. The heart has four chambers and pumps blood in a double circulation which prevents deoxygenated blood from mixing with oxygenated blood.

2. Low pressured deoxygenated blood from rest of body and head are carried into the right atrium by vena cava, while high pressured oxygenated blood from lungs are carried into the left atrium by pulmonary vein.

3. Blood is collected at the right and left atria. Atria muscles relaxed.4. As blood is collected, pressure in the atria increases. Myogenic cells in SAN

pacemaker cause atria to contract as ventricles relax, decreasing pressure in ventricles. Blood force through the atrio-ventricular valves and enter ventricles.

5. As blood empties from atria and fills ventricles, blood pressure increases as pressure in atria decrease.

6. Myogenic cells in SAN pacemaker causes ventricular muscles to contract, blood force through semi-lunar valves as atrio-ventricular valves close to prevent backflow and causes “lub” sound.

7. Blood from left ventricle flow into aorta, blood from right ventricle flow in pulmonary artery. Ventricles relax as pressure decreases and semi-lunar valves close with “dub” sound.

8. For longer distance, thicker left ventricular wall provide high pressure to pump blood from left ventricle through the aorta to the rest of body and head, while for a shorter distance, thinner right ventricular wall provides less to pump blood from right ventricle through pulmonary artery to lungs and exchange carbon dioxide for oxygen.

9. Cycle is complete and begins again.

Muscles & MovementsState the roles of bones, ligaments, muscles, tendons and nerves in human movement.

Bones support muscles and allow movements.Bones act as levers

Tendons attach muscles to bone Ligaments attach bones to bones Antagonistic muscles cause opposite movements Muscles contract and relax to provide force for movements Nerves attached to muscles send impulses carrying signals from CNS for

contraction and control timing of movements

Explain how a muscle fibre contracts, following depolarization of its plasma membrane.1. When muscle is relaxed, the thin protein strand tropomyosin is wrapped around actin

filament, concealing the myosin binding sites.2. After the action potential is received, calcium ions are released from sarcoplasmic

reticulum into the cytoplasm of the muscle cell.3. The calcium binds to troponin.4. Calcium bound troponin changes shape, the movement of tropomyosin exposes

binding sites (for myosin) on actin5. Contraction of muscle fibres is due to the sliding of filaments (over each other).6. Myosin heads bind to actin on the myosin binding sites and form bridges.7. ATP binds to the myosin heads causing them to detach from the binding sites/8. Hydrolysis of ATP occurs. ATP is converted to ADP. Detachment causes myosin

heads to move.9. Myosin pushes and slide actin filaments in one direction towards the centre of the

sarcomere as muscle contracts. The sarcomere shortens.10. Myosin head reattach to myosin binding site further along on actin. ATP binds to

myosin again. Process of sliding continues until calcium ions are released from troponin.

11. Troponin revert back original shape, concealing the myosin binding sites. Mysoin heads can no longer attach to actin, muscle relaxes.

Explain how the action of the muscles is co-ordinated at this joint by the nervous system. muscles are co-ordinated by reflexes from the CNS / spinal cord; the biceps and triceps muscles are antagonistic; contraction of a muscle is stimulated by motor nerves; stretch receptors / proprioreceptors in muscles and tendons sense muscle stretching; when stretch receptors in muscles are stimulated they produce a reflex stimulating muscle contraction / stretch reflex; reciprocal innervation of muscles / when one muscle is excited the antagonistic muscle receives no excitation / is inhibited;

Outline synaptic transmission at the neuromuscular junction of skeletal muscles. neurotransmitter is acetylcholine / cholinergic synapses; action potential arrives and depolarizes the synaptic knob; extra cellular calcium ions enter triggering the release of acetylcholine; acetylcholine diffuses across synaptic cleft; acetylcholine binds to the muscle receptor and depolarizes the post synaptic membrane; acetylcholine is removed by acetylcholine esterase;

Explain how actin and myosin cause muscle contraction. cross bridge formation between actin and myosin heads; repeated cycles of cross bridge formation / ratchet mechanisms and ATP hydrolysis moves the actin filaments; actin filaments pulled toward centre of sarcomere; light bands become more narrow; when acetylcholine is no longer present the sarcoplasmic reticulum reabsorbs calcium ions stopping the process;

DiseaseState the difference between an antigen and an antibody.

Explain antibody production. antigen causes an immune response to produce antibodies specific for that antigen; antibodies produced in B-lymphocytes; B-lymphocytes produced in bone marrow; carried in blood; antigen presenting cell / helper T cell present antigen to B cell;

Describe the cause, transmission and effect of one human bacterial disease.

Explain the cause, transmission and social implications of AIDS. cause:

o human immunodeficiency virus / HIV / HIV 1 and HIV 2;o retrovirus / RNA to DNA;o enters T-helper cells;o immune system becomes disabled / weakened;o greater chance for opportunistic infections;

transmission:o sexually transmitted;o can be transmitted from man to woman / man to man contact / woman to

man /o mother to fetus;o breast milk / saliva and other body fluids;o use of dirty needles;o blood transfusions;

social implications of AIDS:o many orphaned children;o social stigma / discrimination;o problems obtaining employment / life insurance;o impact/costs on health systems of treating people;o early death reduces number of adults / reduces workforce / reduces family

income;o drug treatment expensive;o reduces promiscuity / encourages use of condoms;

Explain why antibiotics are effective against bacteria but not viruses. antibiotics block specific metabolic pathways/cell wall production in bacteria; viruses reproduce using the host cell metabolic pathways; (host cell) pathways are not affected by antibiotics; viruses do not have metabolic pathways;

Gas ExchangeExplain how and why the breathing rate varies with exercise.

oxygen is becoming limited; CO2 concentration builds up in blood; lactic acid builds up in blood; lowers blood pH; chemosensors detect lowered pH; sensors in carotid artery / aorta; send impulses to breathing centre / brain stem; impulse sent to diaphragm; impulse sent to intercostal muscles; increases / decreases rate of breathing / contraction / relaxation of muscles; involuntary control; breathing rate increases to remove more CO2 from blood / lungs;

Many processes in living organisms, including ventilation and gas exchange, involve moving materials. State the differences between ventilation and gas exchange in humans.

ventilation (is) movement of air; movement in and out of the lungs; caused by muscles; an active process; involves mass flow / involves flow along air passages;gas exchange (is) movement of carbon dioxide and oxygen; (occurs when) oxygen moves from lungs / alveoli to red blood cells / carbon dioxide moves to lungs / alveoli from red blood cells; (occurs when) oxygen moves from red blood cells to tissues / carbon dioxide moves to red blood cells from tissues; a passive process / diffusion; takes place across a surface;

Explain the need for, and the mechanism of, ventilation of the lungs in humans. draws fresh air / oxygen into the lungs; removal / excretion of CO2; maintains concentration gradient of O2 / CO2 / respiratory gases; diaphragm contracts; (external) intercostal muscles contract; increased volume (of thorax / thoracic cavity); decreasing air pressure in lungs; air rushes in down air pressure gradient; converse of the above causes exhalation; abdominal muscles contract during active exhalation;

elastic recoil of lungs helps exhalation;

BiochemistryDescribe the use of carbohydrates and lipids for energy storage in animals.carbohydrates:

stored as glycogen (in liver); short-term energy storage; more easily digested than lipids so energy can be released more quickly; more soluble in water for easier transport;

lipids: stored as fat in animals; long-term energy storage; more energy per gram than carbohydrates; lipids are insoluble in water less osmotic effect;

Discuss the possible health problems associated with diets rich in lipids. saturated fatty acids cause high cholesterol; atherosclerosis / narrowing of (lumen of) arteries; CHD / formation of clots / heart attack / heart failure / thrombosis / stroke; hypertension / high blood pressure; obesity / overweight; which is linked to diabetes; although there are also genetic factors / some countries eat a lot of fats and have low CHD;

EnzymesExplain the significance of secondary structure to the structure of a protein.

held together by hydrogen bonds; between CO and NH groups; (α-helix for) structure of fibrous proteins / keratin; one of four levels of structure; provides stability of structure;

o helix;o sheet;

State the name of a competitive enzyme inhibitor. malonate / Prontosil

Outline the difference between competitive and non-competitive enzyme inhibitors. competitive similar to substrate and non-competitive not; competitive attaches to the active site, non-competitive does not bind to the active site; non-competitive changes enzyme shape, competitive does not; competitive change reversible;

Outline the induced fit model of enzyme activity. substrate binds / approaches active site; shape of active site changes; bonds in substrate weaken; activation energy decreases; explains broad specificity of some enzymes; e.g. proteases;

NervesExplain how human perception of the colour yellow would depend on the eye and the brain.

humans have three different cones (with pigments); cones (with pigments) can absorb red, green or blue light; (yellow light will result in) equal stimulation of red and green cones; which synapse with bipolar cells; which synapse with neurons of the optic nerve; which transmit the signal to the visual cortex (in the brain); where yellow colour is perceived;