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Biology:Paper 1 and 2 exam questions
Terms in this set (18)
Where is amylase produced? (1)
Salivary glands and pancreas
Where is maltase produced? (1)
Maltose is hydrolysed by the enzyme maltase.
Explain why maltase catalyses only this reaction. (3)
Active site of maltase is complementary has specific tertiary structure and therefore shape (1). Only maltose (substrate) can bind (2).To form enzyme-substrate complexes (3).
Messenger RNA (mRNA) is used translation to form polypeptides. Describe how mRNA is produced in the nucleus of the cell (6)
DNA helicase (1) breaks the hydrogen bonds, so the double stranded DNA is now two single strands (2). Only of one of the DNA single strands act as a template to be copied (3). The RNA nucleotides are attracted to the exposed bases and bind to the complementary base (4). The enzyme RNA polymerase joins these nucleotides together (5). This forms pre-mRNA which is then spliced to form mRNA (6).
Describe the structure of proteins (5)
The primary structure is a chain/polymer of amino acids (1), joined by peptide bonds (2). The secondary structure of a protein is the folding of a polypeptide chain (either alpha helix or beta pleated) due to hydrogen bonds (3). The tertiary structure is a 3D folding due to hydrogen, disulphide bridges and ionic bonds (4). Finally, the quaternary structure is two polypeptide chains (5).
Describe how proteins are digested in the human gut (4)
Proteins are digested by the hydrolysis of peptide bonds between amino acids (1). Endopeptidases break polypeptides into smaller chains, for instance trypsin. Once the chains are smaller, exopeptidases break the terminal peptide bond so single amino acids are removed (2). One example of a exopeptidase is a dipeptidase, which hydrolyse dipeptides into two single amino acids (3).
What was the purpose of step 2, in which samples were mixed with water, hydrochloric acid and pepsin? (1)
Reproduces conditions/ effect of stomach (1)
What reducing sugar, or sugars would you expect to be produced during chewing? Give a reason for your answer. (2)
Maltose (1) because salivary amylase is produced which hydrolyses starch (2).
In the control experiments, cooked wheat was chopped up to copy the effect of chewing.
Suggest a more appropriate control experiment. Explain your suggestion. (2)
Use boiled saliva instead of cooked wheat chopped up (1) as this will denature amylase (2)
This siRNA would only affect gene expression in cells infected with HIV.
Suggest two reasons why (2)
Only infected cells have the HIV protein on their surface (1). Therefore, only the carrier can attach and therefore siRNA can only enter these cells (2).
siRNA is complementary to one mRNA (1). Only the HIV infected cells contain this mRNA, therefore it can only stop the translation of this gene (2)
The carrier molecule on its own may be able to prevent the infection of cells by HIV. Explain how. (2)
The carrier molecule binds to the HIV protein (1), this prevents the HIV particles from binding to the receptor of a human cell (2).
Oestrogen is a hormone that affects transcription. It forms a complex with a receptor in the cytoplasm of target cells. Explain how an activated oestrogen receptor affects the target cell. (2)
Oestrogen binds to a transcription factor called a oestrogen receptor forming an oestrogen-oestrogen receptor complex (1). This stimulates RNA polymerase which increases transcription (2).
Use Figure 2 to suggest how endoxifen reduces the growth rate of these breast tumours. (2)
Endoxifen is a similar shape to oestrogen and binds with the oestrogen receptor (1) therefore the receptor is not activated so will not attach to promotor region and therefore no transcription (2).
Describe the process of natural selection (5)
Genetic variations between individuals arise from mutations (1). This variation means some are better adapted to selection pressures than others (2). The individuals with the more advantageous alleles (3) are more likely to survive, reproduce and pass on their alleles to offspring (4). Over generations the frequency of the beneficial allies in the gene pool increases (5).
Describe the process of translation (5)
mRNA leaves nuclear pore and attaches to the ribosome (1). Each tRNA has an anticodon which is complementary to a specific codon in the mRNA (2).A second tRNA molecule attaches itself to the next codon in the same way (3). The two amino acids are joined by peptide bonds (4). This process continues until there is a stop signal, the polypeptide chain then moves away from the ribosome and translation is complete (5).
Describe the mass flow hypothesis for the mechanism of translocation in plants (4)
Sugars (sucrose) are actively loaded from companion cells to sieve tubes (1). This lowers the water potential in the sieve tubes so water enters by osmosis (2). This creates a high pressure inside the sieve tubes so causes mass transport from source to sink (roots) (3). When they reach the sink, the sugars are converted for respiration (glucose) or stored (as starch) (4).
Explain how the release of acetylcholine at an excitatory synapse reduces the membrane potential of the postsynaptic membrane (3)
ACh binds to cholinergic receptors (1) which causes Na+ ions to open (2), Na+ ions depolarise the membrane (3) (makes the membrane less negative- increases chance of reaching threshold and therefore firing action potential)
Explain what causes transmissions at a synapse to occur in only one direction (2)
Receptor sites are only in one place, they are only on the membrane of the post-synaptic neurons (1) and neurotransmitter vesicles are only located in pre-synaptic neurons (2)
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