PPQ Imported Biological molecules and cells

Describe chemical reactions involved in conversion of polymers to monomers and monomers to polymers

Monomers react together to form polymers during a condensation reaction where bonds form between the monomers and a water molecule's produced as a by-product. An example of this is the polysaccharide starch being formed from alpha-glucose monomers where glycosidic bonds form between the monomers. A polymer can be converted to its monomers during a hydrolysis reaction where water's added to the polymer and the bonds between the monomers are broken. An example of this is a polypeptide chain being hydrolysed so the peptide bonds between the amino acids break, resulting in the separate amino acids.

Action of protein carrier X is linked to membrane-bound ATP hydrolyse enzyme. Explain function of this enzyme

The active site of the enzyme's complementary to ATP and binds to it forming ESCs. This causes the hydrolysis of ATP to ADP and an inorganic phosphate which provides energy for the Na-K pump to actively transport Na ions out of the cell into the blood and K ions into the cell. This maintains a Na ion concentration gradient so more Na ions and glucose can diffuse into the ileum cell and be absorbed into the blood.

Movement of Na ions out of the cell allows absorption of glucose. Explain how.

Na-K ion pump actively transport Na ions out of the cell and K ions into the cell. This maintains a Na ion concentration gradient between the ileum and the cell lining it. So more Na ions and glucose can move into the cell by facilitated diffusion.

Describe and explain 2 features in a cell specialised for absorption.

1. Folds in the cell membrane so there's a large SA so diffusion and active transport is more rapid.
2. Lots of mitochondria to produce lots of ATP which provides energy for active transport.
3. Large blood supply that constantly transports the products absorbed away from the cell to maintain a concentration gradient so diffusion can continue rapidly into the cell.

Describe how amino acids join to form a polypeptide so there's always NH2 at one end and COOH at the other

The COOH group of one amino acid reacts with the NH2 group of another in a condensation reaction where a molecules of water's eliminated and a peptide bond's formed. The NH2 group of the amino acid on the one end of the polypeptide doesn't react to form a peptide bond and neither does the COOH group in the amino acid on the other end. Therefore a water molecule's not eliminated and an NH2 group's always on one end of the polypeptide and COOH is always on the other end.

ESC formation increases rate of reaction, explain how.

When the ESCs form the substrates bonds are put under tension by the enzyme making them less stable. This reduces the activation energy for the reaction so that a larger proportion of substrate molecules have sufficient energy to react.

Lyxose binds to the enzyme, suggest reason for difference in results with and without lyxose.

When lyxose binds to the enzyme it may cause the enzyme's tertiary structure to change. This would result in the shape of the active site to alter. This makes the enzymes active site more complementary to the ATP and more ESCS form per minute and the rate increases.

Describe how alpha-gal is formed from 2 galactose molecules.

Formed by a condensation reaction where a glycosidic bond's formed between the 2 monomers and a molecule of water's eliminated.

Compare and contrast the structure and properties of triglycerides and phospholipids.

They both contain glycerol and they both have ester bonds between the glycerol and fatty acid tails. Both are also insoluble. However, phospholipids have 2 fatty acid tails and a phosphate group whereas triglycerides have 3 fatty acid tails and no phosphate group. Also, triglycerides are completely non-polar but phospholipids have a polar region due to the hydrophilic phosphate head and a non-polar region due to the non-polar fatty acid tails.

Describe the role of 2 enzymes in semi-conservative DNA replication

DNA helicase causes hydrolysis of the hydrogen bonds between the nucleotide base pairs of the 2 DNA strands to break. After free nucleotides have base paired with the 2 single strands DNA polymerase causes the new nucleotides to join together in a condensation reaction forming phosphodiester bonds between the new nucleotides. Resulting in 2 new DNA molecules each with 1 strand from the original DNA molecule.

Show 3 differences between DNA in the nucleus of a plant cell and DNA in a prokaryotic cell.

1. Plant cell DNA is linear whereas prokaryotic cell DNA is circular
2. Plant cell DNA consists of many chromosomes but prokaryotic DNA only consists of one
3. Plant cell DNA is associated with history proteins but prokaryotic DNA isn't associated with histones