Topic 8 - DNA, Genes and Chromosomes

Question 1

homologous chromosomes

Answer 1

pairs of chromosomes, one maternal and one paternal set. They contain the same genes in the sae loci, but are not genetically identical

Question 2

Prokaryote vs Eukaryote (DNA)

Answer 2

Prokaryote:
- Location of genetic material - cytoplasm (nucleoid)
- Name of molecule - plasmid
- Shape of molecule - circular
- Association with histone protein - No
- Presence of introns - No
- Molecule length - shorter

Eukaryote:
- Location of genetic material - Nucleus
- Name of molecule - Chromosomes
- Shape of molecule - Linear
- Association with histone protein - yes
- Presence of introns - yes
- Molecule length - longer

Question 3

Gene

Answer 3

A section of DNA located at a particular (fixed) site called its locus

Question 4

exons

Answer 4

regions of the gene that are coding (expressed)

Question 5

introns

Answer 5

regions of the gene that are non-coding (not expressed) and do not contain codons needed to make the final protein

Question 6

Non overlapping

Answer 6

each DNA base in each triplet (codon) is only read once

Question 7

Degenerate

Answer 7

most amino acids have more than one triplet (different set of 3 bases can code for the same amino acid)

Question 8

universal

Answer 8

the same triplets of DNA bases code for the same amino acids in all organisms

Question 9

transcription (short)

Answer 9

production of mRNA, using DNA as a template. A gene is transcribed into a mRNA molecule (occurs in the nucleus)

Question 10

translation (short)

Answer 10

production of polypeptides using the sequence of codons carried by mRNA (occurs in the cytoplasm with ribosomes)

Question 11

transcription (long)

Answer 11

• DNA helicase breaks the hydrogen bonds between complementary base pairs which unwinds the double helix, exposing the gene that is to be transcribed
• One of the two DNA strands acts as a template strand
• RNA polymerases attaches to the template strand and lines free RNA nucleotides up with their complementary DNA nucleotide
• This forms pre-mRNA, which is spliced (removal of introns) to form mRNA
• mRNA diffuses out of the nucleus through the nuclear pore
• after RNA polymerase has detached, the DNA rewinds and forms hydrogen bonds between the complementary base pairs

Question 12

translation (long)

Answer 12

• mRNA molecule associates with a ribosome in the cytoplasm
• First 2 codons are now on the ribosome and attract their complementary tRNA molecules (carrying their specific amino acid)
• anticodon of tRNA molecule joins via complementary base pairing, forming hydrogen bonds with the mRNA codons
  …tbc