Topic 2 Cell membrane past paper questions Flashcards
State what is meant by osmosis
- diffusion of water molecules down a water potential gradient through a
partially permeable membrane
Compare and contrast exocytosis and endocytosis (4)
both used to transport large particles
both involve phospholipid membrane vesicles.
Exocytosis is export and endocytosis is import of material
Explain how oxygen molecules can pass directly through the cell membrane
oxygen is small
oxygen is non-polar it can therefore pass between gaps in cell membrane
State what is meant by gene
sequence of bases of DNA that code for a polypeptide.
Describe how the two strands of DNA forming the double helix in a gene are held together.
complementary bases it enables the formation of two hydrogen bonds between adenine and thymine
Explain why each codon for the DNA genetic code must contain at least three bases.
enough codons needed for 20 different amino
acids
four bases are used in the genetic code
triplet code provides enough
Explain how human lungs are adapted for rapid gas exchange. (4)
many small alveoli to provide a large surface area to increase the rate of diffusion
thin epithelium to increase rate of diffusion.
good supply to maintain diffusion gradient.
State what is meant by the term allele. (1)
a version of a gene
Explain how this mutation results in a non-functioning CFTR protein. (4)
there will be different sequence of R groups
therefore the CFTR protein has a different tertiary structure.
because of different types of bonds between the R groups.
therefore the movement of chloride ions through the cell membrane is affected.
Explain why people with cystic fibrosis may develop lung infections. (4)
produces very thick sticky mucus because of reduced water transport from cells.
cilia lining airways are unable to move mucus therefore micro-organism get trapped in the mucus.
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 carries its own specific amino acid to the ribosome.
- anticodon on tRNA binds to codons on the mRNA.
- tRNA holds the amino acid in place while peptide bonds form.
Explain how the primary structure of collagen determines its properties. (4)
- insoluble because 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
Explain why only five amino acids are coded by this sequence of bases (2)
because three bases form one code for one amino acids.
because there is no stop codon in this sequence.
Explain why some amino acids such as alanine, have more than one genetic code. (3)
- because it’s a degenerate code which means they are more codes than needed.
- arranging the four bases in triplets gives 64 possible
combinations and there are 20 amino acids to code for and stop codons.
minimises the effect on mutations.
Explain the role of the other three genetic codes. (2)
- remaining codes are stop codons on RNA.
- therefore no more amino acids can be added to the
polypeptide chain.
State what is meant by the term semi-conservative replication? (2)
- an increase in the number of DNA molecules
- each new molecule consists of one parent strand and one new strand.
Name one enzyme involved in semi-conservative replication. (1)
DNA polymerase
Explain the importance of semi-conservative replication in the production of new cells. (1)
because it results in genetically identical daughter cells. They will have the same structure as the parent cell.
Compare and contrast the structure of messenger RNA (mRNA) with the structure of transfer RNA (tRNA).
both contain RNA nucleotides
both are single stranded
mRNA is a straight chain and tRNA is folded
size of mRNA is variable and the size of tRNA is constant.
Describe the effects of cholesterol and temperature on membrane permeability, as shown in the graph
As the cholesterol increases the membrane permeability decreases
As temperature increases the membrane permeability increases.
cholesterol has a greater effect on membrane permeability at high temperatures.
Describe the effects of cholesterol and temperature on membrane permeability, as shown in the graph
As the cholesterol increases the membrane permeability decreases
As temperature increases the membrane permeability increases.
cholesterol has a greater effect on membrane permeability at high temperatures.
Explain why cholesterol and temperature affect membrane permeability
because an increase in temperature increases the movement of phospholipids
because the cholesterol decreases the fluidity of the membrane
Explain which of the four bases P, Q, R or S is adenine?
R because it forms hydrogen bonds
R because it has a large base.
Suggest two reasons why prenatal testing for brittle bone disease is not offered to all pregnant women.
- they may not be a family history to this condition
- cost being high.
Explain what is meant by the term gene mutation.
a change in base sequence of DNA coding for a particular polypeptide.
Compare endocytosis with exocytosis. (2)
both involve the formation of a vesicle.
endocytosis takes substances into the cell and exocytosis removes substances from the cell.
both need energy.
Suggest two reasons why a change in one amino acid in prothrombin may have no effect on the blood clotting process. (2)
Prothrombin has different primary sequence of amino acids.
change in tertiary structure of prothrombin.
Describe the role of RNA molecule in the synthesis of a protein using this section of DNA as a template.
complementary mRNA strand is formed.
mRNA moves into the cytoplasm.
mRNA associates with ribosomes.
Describe the process of DNA replication.
DNA molecule unwinds
DNA mononucleotides line up alongside both DNA strands by complementary base pairing.
Hydrogen bonds forming between DNA bases.
Formation of phosphodiester bonds between adjacent DNA mononucleotides.
Explain the roles of RNA in translation.
mRNA is a copy of the genetic code
mRNA carries a genetic information to the ribosomes.
tRNA carries a specific amino acid.
tRNA holds the amino acids in place while the peptide bond form.
State what is meant by the term enzyme
biological catalysts
Explain why it is necessary to measure the initial rate of reaction when investigating the effect of substrate concentration on enzyme activity
as the reaction proceeeds the substrate is used up.
therefore substrate limits the rate of the reaction and substrate becomes the limiting factor.
