Topic 4A: DNA, RNA and Protein Synthesis

Question 1

What is a genome?

Answer 1

• Complete gene set in a cell

Question 2

What is a proteome?

Answer 2

• Full range of proteins a cell can produce

Question 3

How is DNA stored in eukaryotic cells?

Answer 3

• In the nucleus
• Long, linear
• Coiled using histone proteins to form chromosomes

Question 4

How is DNA stored in prokaryotic cells?

Answer 4

• Short, circular
• Coiled - condenses by supercoiling
• No histones
• No introns

Question 5

How is DNA stored in mitochondria and chloroplasts?

Answer 5

• Similar to in prokaryotes
• Circular, shorter
• No histone proteins

Question 6

What are genes?

Answer 6

• Sequence of DNA bases coding for a polypeptide or functional RNA
• 3 bases code for an amino acid and sequence dictates primary structure

Question 7

What are introns?

Answer 7

• Non-coding regions

Question 8

What are exons?

Answer 8

• Coding regions of DNA

Question 9

What are multiple repeats?

Answer 9

• Outside of genes
• Sequences of repeating bases
• Do not code for things

Question 10

What are alleles?

Answer 10

• Different form of a gene
• Slightly different order of bases
• Produce slightly different versions of a polypeptide

Question 11

What are homologous chromosomes?

Answer 11

• Pairs of matching chromosomes
• Same size
• Same genes but can have different alleles
• Genes for same characteristic found on fixed points - loci

Question 12

Why is DNA described as degenerate?

Answer 12

• There are more possible triplet combinations than there are amino acids to code for
• 64 combinations, 20 amino acids
• Some amino acids are coded for by multiple triplets

Question 13

How is DNA non-overlapping?

Answer 13

• Base triplets do not share bases
• Each are read in sequence, separate from the triplet before and after

Question 14

How is DNA universal?

Answer 14

• Same base triplets code for amino acids in all organisms
• Transferable

Question 15

How is mRNA structured?

Answer 15

• Single polynucleotide strand
• Has groups of three bases - codon

Question 16

How is mRNA made / needed?

Answer 16

• Made in transcription to move genetic information from nucleus to ribosome

Question 17

How is tRNA structured?

Answer 17

• Single polynucleotide strand
• Folded into a clover shape
• Hydrogen bonds between specific base pairs hold the shape
• 3 bases on one end - anticodon
• Amino acid binding site on other end

Question 18

Describe the stages if transcription.

Answer 18

• DNA unwinds as DNA helicase breaks H bonds and bases are exposed
• RNA nucleotides line up with complimentary base pairs as one strand acts as a template (A-U)
• RNA polymerase joins the nucleotides together with phosphodiester bonds
• RNA polymerase moves down, assembling the mRNA
• H bonds form in the DNA once RNA polymerase moves on and it recoils
• When the stop codon is reached, RNA polymerase detaches and mRNA is made

Question 19

What is splicing?

Answer 19

• In eukaryotes, introns and exons copied to make pre-mRNA
• Introns removed (spliced) and exons joined to form mRNA
• mRNA leaved nucleus via nuclear pores

Question 20

How is mRNA modified in prokaryotes and why?

Answer 20

• No modification needed
• No introns present

Question 21

Describe translation

Answer 21

• mRNA attaches to ribosome at start codon
• tRNA with complimentary anticodon binds to first triplet and another binds to the second triplet
• Amino acids attached to tRNA are joined by peptide bonds - needs ATP and an enzyme
• First tRNA moves away leaving the amino acid behind
• Ribosome then moves down and next tRNA can bind
• Process continues until stop codon is reached and ribosome detaches leaving the amino acid chain