4.1 DNA, genes and chromosomes

Question 1

How is DNA stored differently in eukaryotes vs. prokaryotes?

Answer 1

Eukaryotic DNA: Long, linear, associated with proteins called histones, tightly coiled into chromosomes (DNA molecule + its associated proteins)

Prokaryotic DNA: Short, circular, not associated with proteins/histones

Question 2

What organelles have their own DNA?

Answer 2

Mitochondria and chloroplasts in eukaryotic cells
- Similar to prokaryotic DNA - short, circular, not associated with proteins/histones

Question 3

Define gene:

Answer 3

Sequence of DNA bases that codes for:
- The amino acid sequence of a polypeptide
- A functional RNA e.g. ribosomal RNA and tRNAs

Question 4

What is a locus?

Answer 4

A gene occupies a fixed position, called a locus, on a particular DNA molecule

Question 5

Define DNA triplet:

Answer 5

Sequence of 3 bases coding for specific amino acid

Question 6

What are the three features of the genetic code?

Answer 6

Universal
- The same specific DNA base triplets code for the same amino acids in all living organisms - e.g. UAU codes for tyrosine in all organisms

Non-overlapping
- Discrete, each base can only be used once and in only one triplet

Degenerate
- The same amino acid can be coded for by more than one base triplet
- e.g. tyrosine can be coded for by UAU or UAC

Question 7

In eukaryotes, much of the DNA doesn’t code for polypeptides…

Answer 7

Introns - non-coding region
Exons - codes for amino acid sequences, which are separated by one or more introns

Question 8

Define genome:

Answer 8

The complete set of genes in a cell, including those in mitochondria and/or chloroplasts

Question 9

Define Proteome:

Answer 9

The full range of proteins that a cell/genome is able to produce

Question 10

Define alleles

Answer 10

Different version (sequence of bases / triplets) of the same gene

Question 11

Define homologous pair of chromosomes:

Answer 11

Same size chromosomes with same genes, but different
alleles