3.4.1 DNA, Genes And Chromosmes

Question 1

Compare the structure of DNA between EUK and PRO

Answer 1

Eukaryotes vs Prokaryotes,

Length: very long vs short
Shape: linear vs circular
No. Per cell: variable vs 1
Associated with proteins: histones vs no

Question 2

What are bases called in: DNA, mRNA & tRNA

Answer 2

• TRIPLET in DNA
• CODON in mRNA
• ANTICODON (at complimentary site only) in tRNA

Question 3

Describe the DNA in eukaryotic cells

Answer 3

• linear DNA molecules, exist as chromosomes - made up of one long molecule of DNA.
• DNA molecule is very long - so wound up so it can fit in the nucleus
• DNA is wound around proteins called histones
• histones help support the DNA
• DNA then coiled very tightly to make compact chromosome

Question 4

DNA molecules in Prokaryotes

Answer 4

• carry DNA as chromosomes
• DNA molecule is shorter and circular
• DNA not wound around histones - it condenses to fit in the cell by supercoiling

Question 5

What is a gene ?

Answer 5

• sequence of DNA bases that codes for either a polypeptide or functional RNA
• the order of the bases in the gene determines the order of a.a in the polypeptide

Question 6

Role of functional RNA

Answer 6

• DNA is copied into mRNA
• genes that don’t code for a polypeptide, code for functional RNA instead
• they perform special tasks during protein synthesis

Question 7

Define genome

Answer 7

• complete set of genes in the cell

Question 8

Introns, exons and non-coding repeats

Answer 8

Introns = genes that don’t code for polypeptides, contain sections that don’t code for a.a
- introns removed during protien synthesis - so they don’t effect the a.a order

Exons = all bits of the gene the do code for a.a

Non-coding repeats = regions of multiple repeats outside of genes
- DNA sequences that repeat over and over
- don’t code for a.a

Question 9

What is the genetic code ?

Answer 9

Sequence of base triplets in mRNA that code for specific a.a

Question 10

Degenerate, on-overlapping and universal genes

Answer 10

Degenerate = some a.a are coded for by more than one base triplet

Universal = the same specific base triplets code for the same a.a in all living things

Non-overlapping = triplets don’t share their bases

Start or stop codons = found at the start and end of the mRNA, tell the cell when to start and stop production of protein