Exam questions Flashcards
Describe how an unsaturated triglyceride is synthesised (3)
- one glycerol and three fatty acids
- joined by condensation reactions/ester bonds
- by enzymes
- one fatty acids is unsaturated/has CC double bond
Explain the role of collagen in the wall of the aorta (2)
- gives the wall strength
- so that the aorta doesn’t get damaged/can withstand pressure of blood
Proteases are enzymes that break down proteins
Explain how a protease breaks down elastin (3)
- active site of protease {binds to/fits} the elastin substrate
- activation energy is lowered by protease
- breaking the peptide bonds
- by hydrolysis
Describe the arrangement of phospholipids in the cell membrane in the fluid mosaic model (3)
- a phospholipid bilayer/2 layers
- polar/hydrophilic phosphate heads pointing outwards/aqueous environment
- non-polar/hydrophobic fatty acid tails pointing inwards/away from water
Describe the structure of a mRNA molecule (3)
- single stranded
- consists of ribose, phosphate and a base
- phosphodiester bonds between mononucleotides
- adenine, uracil, cytosine and guanine
Compare and contrast the structure of a triglyceride and a phospholipid (3)
similarities:
- both contain a glycerol
- both contain fatty acids
- both contain ester bonds
differences:
- triglycerides have three fatty acids whereas a phospholipid only has two
- a phospholipid contains a phosphate group whereas a triglyceride does not
Explain why the properties of LDLs enable cholesterol to be transported in the blood (3)
- {protein/phosphate heads/hydrophilic heads} are {soluble/hydrophilic/polar} and interact with blood/plasma
- fatty acids/triglycerides/cholesterol is insoluble/non-polar/hydrophobic
- therefore cholesterol is surrounded by fatty acid tails/triglycerides
Explain why an increase in temperature increases the fluidity of the membrane (2)
- because phospholipid/molecules have more kinetic energy
- because forces/interactions between fatty acid chains/phospholipids break
- therefore phospholipids can move around within the phospholipid bilayer more
State what is meant by the term osmosis (1)
- diffusion of water molecules down a water potential gradient through a semi-permeable membrane
Explain why oxygen molecules can pass directly through the cell membrane (3)
- oxygen is a small molecule
- oxygen is non-polar
- therefore can pass through gaps in the cell {membrane/hydrophobic tails}
Describe the structure of a nucleotide pair (3)
- contains deoxyribose/pentose/5 carbon sugar, phosphate and bases
- mononucleotides are held together by hydrogen bonds
- between complementary base pairs
State what is meant by the term gene (1)
- sequence of bases of DNA that codes for a polypeptide chain
Describe how the two strands of DNA forming the double helix in a gene are held together (2)
- complementary base pairing (A,T and C,G)
- enables the formation of two hydrogen bonds between adenine and thymine and three hydrogen bonds between cytosine and guanine
State what is meant by the term semi-conservative replication (2)
- increase in the number of DNA {molecules} (two new molecules are made from one molecule)
- each new molecule consists of one {parent/one original/old} strand and one new strand
Explain the importance of semi-conservative replication in the production of new cells (2)
- because it results in genetically identical daughter cells
- that will have the same structure and function as the parent cell
Describe the roles of messenger RNA (mRNA) and transfer RNA (tRNA) in protein synthesis (4)
mRNA-
- is a copy of the {code/DNA/sequence/genes}
- mRNA {moves/carries code} out of the nucleus/to the ribosomes
tRNA-
- {binds to/carries} its specific amino acid
- tRNA anticodon binds to the mRNA codon
- holds the amino acid in place until the peptide bonds have formed
Collagen is an insoluble, fibrous protein
Describe the roles of RNA in the synthesis of collagen (5)
- an mRNA molecule codes for each of the polypeptide chains in collagen
- mRNA carries a copy of the genetic code for collagen out of the nucleus to ribosome
- each tRNA molecule carries its own specific amino acid to the {ribosome/mRNA}
- anticodon on tRNA binds to the codon on the mRNA
- tRNA holds the amino acid in place whilst the peptide bonds forms
- start codon and stop codons on mRNA begin and end synthesis
Explain how the primary structure of collagen determines its properties (4)
- insoluble as there are hundreds of amino acids
- insoluble because there are many hydrophobic R groups
- strong because of the triple helix
- therefore there are many repeating amino acid sequences
- many small R groups so the triple helix can be formed
Explain why some amino acids have more than one genetic code (3)
- because it is a degenerate code
- which means there is more codes than number of amino acids
- arranging the four bases in a triplet gives 64 possible combinations and there are 20 amino acids to code for
- minimises the effect of mutations
Explain the role of the other three genetic codes (2)
- remaining codes are stop codons
- therefore no more amino acids can be added to the polypeptide chain
Compare and contrast the structure of an mRNA molecule with that of a tRNA molecule (3)
similarities:
- both consists of RNA/mononucleotides/ribose sugar/phosphodiester bonds/U,A,C,G
- both are single stranded
differences:
- mRNA has codons whereas tRNA has anticodons
- tRNA has hydrogen bonds whereas mRNA does not (tRNA clover shape/folded whereas mRNA is linear)
- tRNA has an amino acid binding site whereas mRNA does not
Explain why a mutation might lead to a change in the activity of an enzyme (4)
- mutation results in a different sequence of amino acids
- therefore different R groups/side chains
- results in different {ionic/hydrogen/disulphide} bonds forming
- changes the shape of the active site, changing the activity of the enzyme
Describe an experiment that could be carried out to investigate the effect of enzyme concentration on the initial rate of reaction (4)
- range of different enzyme concentration (at least 5)
- idea of substrate not limiting
- reference to mixing substrate and enzyme
- description of how to measure the dependent variable with time
- description of how to measure the initial rate of reaction
- controlled variables e.g. temperature/volume/concentration of substrate
- repeat each enzyme concentration
- use a control such as distilled water for comparison
State why enzymes are described as biological catalysts (1)
- proteins which reduce the activation energy of a biological reaction