Question
(a) Label the parts of the DNA diagram indicated by I, II, III and IV.
b.(i) State one role of nucleosomes in eukaryotic cells.
(ii) Outline how Hershey and Chase’s experiment provided evidence for DNA as the genetic material.
(iii) State one function for a region of DNA that does not code for proteins.
c.Outline the role of the following in translation.
(i) A-site of ribosomes
(ii) tRNA activating enzymes
Answer/Explanation
Ans:
a)
a. I. cytosine (NOT simply Nitrogenous base)
b. II. sugar phosphate/covalent/phosphodiester bond
c. III. phosphate (NOT phosphorus)
d. IV.deoxyribose (NOT pentose sugar)
b (i)
a. help to supercoil/pack DNA in chromosomes
b. help to regulate transcription / gene expression
b (ii)
a. experiment is meant to determine whether DNA or protein is the genetic material
b. viruses/bacteriophages grown in radioactive S/S35 which enters the protein coat
c. viruses/bacteriophages grown in radioactive P/P32 which enters the DNA
d. «radioactive» viral DNA entered the bacterial cell during infection
OR
«radioactive» viral protein did not enter the bacterial cell during infection
b (iii) regulator of gene expression/introns/telomeres/genes for tRNA / rRNA / promoter / enhancer / silencer / site for primer to bind / codes for mRNA primer
c (i) binding/entry of tRNA carrying amino acids/aminoacyl tRNA / charged tRNA / site of transfer of growing polypeptide chains/peptide bond formation
c (ii)
a. ATP «hydrolysis» provides energy for amino acid attachment
b. they attach a specific amino acid to the (3′ ) end / free CCA of a tRNA
Question
The micrograph shows a plant cell of Lilium grandiflorum during meiosis.
a. (i) Identify, giving reasons, the stage of meiosis shown by this cell.
(ii) Outline the law of independent assortment.
b. The genes for cystic fibrosis and blood group are not linked. Two parents are heterozygous for cystic fibrosis. One parent has blood group O and the other has blood group AB. Using a Punnett square, determine the probability that their child will have both cystic fibrosis and blood group A.
Answer/Explanation
Ans:
a (i)
a. anaphase II
b. as four daughter cells are being formed
OR
the centromeres split / sister chromatids separate
OR
sister chromatids/ chromosomes are pulled «by the spindle microtubules» to opposite poles
a (ii)
a. two «or more» traits/genes are inherited independently of one another Accept vice versa.
b. observed for traits/genes that are not linked/far apart on the chromosome
c. «due to homologous» chromosomes aligning independently/randomly on equator during metaphase I/meiosis I
d. during anaphase I homologues pulled to separate poles
b)
a. correct parental genotypes shown / Ff ii, FfIA IB