Explain Photosynthesis

unit 1 - AS biology

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  • Created on: 12-05-11 09:44

Explain Protein Synthesis

Transcription - takes place in the nucleus - DNA Helix unzips: DNA helicase (enzyme) - hydrogen bonds break - this exposes template strands, the 3 bases called 'a triplet' - RNA nucleotides pair with bases of DNA - mRNA produced, 3 bases called a codon ( thymine replaced by uracil) - leaves nuclear pore into cytoplasm.

Translation - takes places in the ribosomes in the cytoplasm - tRNA pairs it's 3 bases (anti-codon) with the exposed codon of the mRNA - hydrogen bonds form between bases - attached to each tRNA in a specific amino acid - amino acid sequence is a polypeptide - joined by peptide bonds - new protein made.

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How is water regulated in the mucus

Too much water - Na+ is actively pumped across the basal membrane - Na+ diffuses through sodium channels in the apical membrane - Cl- diffuses down the electrical graident - water is drawn out of the cells by osmosis due to high salt concentration in the tissue - water is drawn out of the mucus by osmosis.

Too little water - Cl- is pumped into cell across basal membrane - Cl- diffuses through the open CFTR channels - Na+ diffuses down the electrical gradient - elevated salt concentration in the mucus draws out the cell via osmosis - water is drawn into mucus via osmosis.

With CF - CFTR channel is absent or not functional - Na+ channel is permanently open - water is continuously removed from the mucus via osmosis.

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Describe the process of a blood clot

Name for a blood clot is a 'thrombosis' - blood clots form from slow flowing blood or whe endothelium is damaged - platelets come into contact with damages area and change from flat to sperical with long projections, causing a platelet plug - soluble plasma protein prothrombin is converted into thrombin - thrombin is an enzyme that catalyses the fibrinogen reaction - fibrinogen is another soluble plasme protein that changes into fibrin - fibrin is an insoluble protein, that act as a 'mesh' trapping everything inside.

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Descrive the process of Atherosclerosis

The endothelium becomes damaged, maybe by high blood pressure or toxins - inflammatory response occurs, which means white blood cells move into the damaged area. - These accumilate cholesterol, which leads to a deposit known as an 'atheroma'. - Calcium salts and fibrous tissue also build up, this hardens and is now a plaque. this reduces the elasticity of the artery. - Due to the narrowing of the artery, blood pressure will increase, this process is known as positive feedback as it will cause more damage to the artery.

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Explain all the different saccharides

Saccharies and Carbohydrate general formula is - Cx(H2O)n

Monosaccharides (CH20) are single sugar molecules e.g. glucose, fructose and galactose. (+ lactose)

Disaccharides are 2 single sugar molecules combined - formed by condensation reaction producing glycodisic bonds, e.g. maltose (2 glucose molecules) , sucrose (glucose+fructose) galactose (glucose+lactose)

Polysaccharides are many monosaccharides joined via a condensation reaction making glycosidic bonds.  - e.g. starch (storage molecule), compact low solubility with the little osmotic effect. Made of amylose, 200-5000 glucose molecules - straight chain - 1'4 glycosidic bond link.
As well as, Amylopectin (also a polymer of glucose molecules) - 1'6 glycosidic bond causing it to branch.

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Examples and Descriptions of Lipids


- 3 fatty acids and 1 glycerol - condensation reaction occurs, removing water. - Ester bond formed.

Saturated - maximum no. of Hydrogen molecules - no double carbon bond - animal fats and dairy products - closely packed with strong intermolecule forces = solid ( -butter)

Monosaturates - only 1 double bond between carbon atoms in each fatty acid

Polyunsaturates - more then 1 carbon-carbon double bond. - Double bonds cause 'kinks' in chains that are not closely packed, they have weak intermolecular bonds = Liquids (-oil)

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Compare Arteries and Veins

Arteries - narrow lumen - more smooth muscle, elstic fibres and collogen (tough + durable) - Thicker walls - no valves - oxygenated blood AWAY from heart, except Pulmonary Artery - Deoxygenated blood from right atria to lungs.

Veins - wider lumen - less smooth muscles, elastic fibres and collogen - Thinner walls - valves - Deoxygenated blood FROM heart, except Pulmonary Vein - Oxygenated blood from lungs to left atria.

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Explain Cardiac Cycle

ATRIAL SYSTOLE- pressure in the atria increase due to blood returning from veins - increased pressure opens the atrioventricular valves - allowing blood to enter ventricles - atria contracts forcing and remaining blood down.

VENTRICULAR SYSTOLE - ventricles contract from apex of heart upwards - increasing pressure and therefore closing the atrioventricular vavles - the semilunar valves open and blood does into the arteries,

DIASTOLE - as the atria and ventricles relax, pressure falls - a decrease in pressure of ventricles causes the semilunar valves to close - decrease in pressure in atria means blood is drawn into the heart from the veins.

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What are the methods of Transport?

Active Transport - the NET movement of molecules from an are of high concentration to low concentration until equilibrium is reached.
Passive - no energy required, - hydrophobic molecules.

Falicated diffusion - area of high-low concentration until equilibrium is reached - through channel proteins or via carrier proteins that change shape. - passive, no energy required.
Osmosis - a type of diffusion involving water molecules - from area of high to low concentreation - passive - no energy required.
Active Transport - against the concentration gradient through carrier preoteins, requires ATP.

EXOCYTOSIS - used for bulk transport out of the cell - vesicles fuse with the cell surface membrane.

ENDOCYTOSIS - used for bulk transport of substances into the cell - vesicles are created from cell surface membrane.

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Explain the 4 stages of Protein Structure

Primary - 2 amino acids joined by condensation reaction, making a dipeptide or polyperptide (3+) - peptide bonds form between the amino acids - proteins are made from 2 or more of these polypeptide chains - the sequence of the amino acids in the chain is known as the primary structure.

Secondary - interactions of the amino acids may cause the chain to twist - coiling to form an 'alpha helix', hyrdogen bonds form between C=O and -NH, stabilises shape. - Several chains may link together with hydrogen bonds holding the 'parallel chains' together - known as 'beta pleated sheets'

Tertiary - polypeptide chains often bend and folds to produce a precise 3 dimentional shape - disulphide bridges formed stabilising molecule. - R groups become polar, attracting water (hyrdophilic) non polar groups are hydrophobic - e.g. enzymes.

Quaternary - only when there are multiple polypeptide chains e.g. haemoglobin.  

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