3.4.1 DNA, Genes and Chromosomes

Question 1

(DNA, Genes & Chromosomes) Describe the structure of chromosomes in prokaryotes.

Answer 1

Shorter, circular loop of DNA (loose in cytoplasm). Is NOT associated with proteins.

Question 2

(DNA, Genes & Chromosomes) Describe the structure of chromosomes in eukaryotes.

Answer 2

• Associated with proteins called histones.
• Chromosome only visible during cell division (mitosis) when DNA is condensed.
• Interphase - one DNA double helix dispersed.
• Cell division - 2 DNA molecules called chromatids which are genetically identical and supercoiled.
• Each chromosome is linear and has many genes along its length.

Question 3

(DNA, Genes & Chromosomes) What is a chromosome formed from?

Answer 3

A DNA molecule and its associated proteins.

Question 4

(DNA, Genes & Chromosomes) Describe the mitochondria and chloroplasts of eukaryotic cells.

Answer 4

Contain DNA which is short, circular and not associated with protein (like the DNA of prokaryotes).

Question 5

(DNA, Genes & Chromosomes) What is gene?

Answer 5

Section of DNA that contains a specific nucleotides base sequence.

Question 6

(DNA, Genes & Chromosomes) What does a gene encode for? (2)

Answer 6

1. Sequencing amino acids during protein synthesis (translation) determining the tertiary structure of a single polypeptide.
2. Functional RNA (mRNA, tRNA, rRNA)

Question 7

(DNA, Genes & Chromosomes) What is a ‘gene locus’?

Answer 7

The fixed position of each gene along a chromosome.

Question 8

(DNA, Genes & Chromosomes) What is a triplet, and what does it code for?

Answer 8

A triplet is sequence of three DNA bases, and it codes for a specific amino acid.

Question 9

(DNA, Genes & Chromosomes) What are the features of the genetic code?

Answer 9

20 different amino acids exist
Each amino acid has its own code of DNA bases
4 different bases (A,T, C and G)
Triplet code of 4x4x4 bases = 64 triplets (codons)

• Each triplet (codon) encodes for one specific amino acid
• Degenerate
• Non-overlapping
• Universal

Question 10

(DNA, Genes & Chromosomes) What is meant by the term ‘degenerate’ regarding the genetic code?

Answer 10

Amino acids can have more than one codon.

Question 11

(DNA, Genes & Chromosomes) What is meant by the term ‘non-overlapping’ regarding the genetic code?

Answer 11

Each base is only read once.

Question 12

(DNA, Genes & Chromosomes) What is meant by the term ‘universal’ regarding the genetic code?

Answer 12

Each codon codes for the same amino acid in all organisms.

Question 13

(DNA, Genes & Chromosomes) Explain the difference between introns and exons with eukaryotic genes.

Answer 13

DNA of eukaryotic genes have base code sections that encode for proteins (polypeptide) called exons AND sections of called introns that do not.

Question 14

(DNA, Genes & Chromosomes) In eukaryotes, much of the nuclear DNA NOT code for?

Answer 14

Polypeptides.

Question 15

(DNA, Genes & Chromosomes) Within a gene, what are exons are separated by.

Answer 15

One or more intron (non-coding sequence).

Question 16

In eukaryotes, there are ___-______ multiple repeats of ____ sequences between genes.

Answer 16

Non-coding
Base