3.4.1.1 DNA, genes and chromosomes

Question 1

What is a gene?

Answer 1

A gene is a section of DNA that contains the coded information for making polypeptides and functional RNA.

Question 2

What is the locus?

Answer 2

A locus is the position of a gene on a chromosome

Question 3

What factors determine the nature and development of all organisms?

Answer 3

Genes and environmental factors

Question 4

The genetic code uses 4 different DNA bases. What is the maximum number of different DNA triplets that can be made from these 4 bases?

Answer 4

4^3 = 64

Question 5

What are some of the features of genetic code?

Answer 5

•It’s degenerative •It’s non-overlapping (each base only ready once) •It’s universal

Question 6

Why is genetic code described as “degenerative”?

Answer 6

As one amino acid can be coded for by more than one triplet

Question 7

Why is the genetic code described as being “universal”?

Answer 7

In all organisms the same triplet codes for the same amino acid;

Question 8

What are exons?

Answer 8

Sequence that codes for amino acids.

Question 9

What are introns?

Answer 9

Non-coding sequences (not ITNRested in them)

Question 10

Why is the genetic code described as “non-overlapping”?

Answer 10

Each base in the sequence is only read once

Question 11

Describe the DNA in prokaryotic cells

Answer 11

•DNA molecules are shorter •They form a circle •They aren’t associated with proteins (histones) •NO chromosomes

Question 12

Describe the DNA in eukaryotic cells

Answer 12

•DNA molecules are longer •They form a line (linear) •They occur in association with proteins called HISTONES to form chromosomes

Question 13

What is an allele?

Answer 13

Different form of a gene

Question 14

Explain why the DNA base sequences of homologous chromosomes are almost the same.

Answer 14

Homologous chromosomes have the same genes At the same loci Different alleles (different forms of the same gene) usually only have a small difference in their base sequence

Question 15

What name is given to the different forms of a gene?

Answer 15

Allele

Question 16

Which 2 biological molecules make up a ribosome?

Answer 16

ribosomal RNA (rRNA) and Amino acids

Question 17

Describe the shape of a replicated chromosome

Answer 17

2 sister chromatids held together by centromere

Question 18

what is this a picture of?

Answer 18

Nucleotide

Question 19

Identify the blue circle in this nucleotide

Answer 19

phosphate

Question 20

Identify the green shape in this nucleotide

Answer 20

deoxyribose (pentose sugar)

Question 21

Indentify the pink rectangle in this nucelotide

Answer 21

organic base - either A T G or C

Question 22

If there is 18% adenine in a DNA sample what % will be thymine?

Answer 22

18

Question 23

If there is 18% adenine in a DNA sample what % will be guanine?

Answer 23

32

Question 24

name the enzyme involved in DNA replication

Answer 24

Helicase AND DNA polymerase

Question 25

What is a homologous pair of chromosomes?

Answer 25

2 chromosomes that carry the SAME genes (different alleles)

Question 26

why is the genetic code described as being universal?

Answer 26

same triplet codes for same amino acid in all organisms

Question 27

how does deletion lead to the production of a non-functional protein?

Answer 27

• deletion changes amino acid sequence
• causes frame-shift
• changes tertiary structure

Question 28

a change from Glu to Lys at amino acid 300 had no effect on the rate of reaction catalysed by the enzyme. the same change at amino acid 279 significantly reduced the rate of reaction catalysed by the enzyme.

suggest reasons for the differences between the effects of these 2 changes?

Answer 28

• negatively charged to positively charged change in amino acid
• change at amino acid 300 doesnt change shape of active site
• amino acid 279 may have been involved in an ionic/disulfide/hydrogen bond SO shape of active site changes