DNA and genetic code

Question 1

When preparing the cells for observation the scientist placed them in a solution that had a slightly higher (less negative) water potential than the cytoplasm. This did not cause the cells to burst but moved the chromosomes further apart in order to reduce the overlapping of the chromosomes when observed with an optical microscope.

Suggest how this procedure moved the chromosomes apart.

Answer 1

Water moves into the cells/cytoplasm by osmosis;

Reject water moving into chromosomes/nucleus.

2. Cell/cytoplasm gets bigger;

Accept idea of cell/cytoplasm has greater volume/swells/expands.

Question 2

The dark stain used on the chromosomes binds more to some areas of the chromosomes than others, giving the chromosomes a striped appearance.

Suggest one way the structure of the chromosome could differ along its length to result in the stain binding more in some areas.

______________________________________

Answer 2

Differences in base sequences

OR

Differences in histones/interaction with histones

OR

Question 3

What is a homologous pair of chromosomes

Answer 3

Two chromosomes that) carry the same genes

Question 4

what is the role of stop codons

Answer 4

Stop translation;

2. Result in detachment of polypeptide chain from ribosome.

Question 5

Suggest one advantage of showing the genetic code as base sequences on mRNA, rather than triplets on DNA.

Answer 5

(Because) ribosomes assemble polypeptides using mRNA code

OR

DNA has two strands each with a different (complementary) base sequence;

Question 6

Name the bases represented in the table by:

Answer 6

A = adenine

C = cytosine

G = guanine

U = uracil

Question 7

Non-overlapping __

Answer 7

each base is part of only one triplet.

Question 8

Explain how a gene codes for a protein.

Answer 8

Base sequence (on DNA/in gene);
Determines sequence of amino acids;
By determining base sequence on (messenger) RNA;
Code is a triplet code/three base code for an amino acid

Question 9

vWhat are homologous chromosomes?

Answer 9

Pairs of chromosomes/two chromosomes;
With genes for same features / with same genes;
At same loci / in same sequence;

Question 10

Why is the genetic code described as being universal?

Answer 10

(In all organisms / DNA,) the same triplet codes for the same amino acid;