3.4.1 DNA, genes and chromosomes, 3.4.2 DNA and protein synthesis

Question 1

Compare DNA in prokaryotic and eukaryotic cells?

Answer 1

Prokaryotic DNA:
- short
- circular
- not associated with proteins

Eukaryotic DNA:
- long
- linear
- associated with proteins (histones)

In eukaryotic cells mitochondria and chloroplasts contain prokaryotic like DNA

Question 2

What is a gene?

Answer 2

• DNA base sequence
• that codes for the amino acid sequence of a polypeptide or a functional RNA

Question 3

What is a locus?

Answer 3

The fixed position a gene occupies on a particular DNA molecule

Question 4

What is the difference between a triplet and a codon?

Answer 4

• A triplet is a sequence of 3 DNA bases
• That codes for a specific amino acid
• A condon is a sequence of 3 mRNA bases
• that code for an amino acid

Question 5

Give 3 features of genetic code and that they mean

Answer 5

• universal: same triplets code for the same amino acids in all organisms
• non-overlapping: each DNA nucleotide base only part of one triplet
• degenerate: most amino acids are coded for by more than one triplet

Question 6

What is the genome and protogenone?

Answer 6

• genome - complete set of genes in a cell of an organism
• protogenome - the complete set of proteins a cell can produce

Question 7

What are introns and exons?

Answer 7

• introns: non-coding DNA base sequences (spliced out from mRNA after transcription)
• exons: coding regions of DNA base sequence (left after introns are removed)

Question 8

Compare DNA, mRNA and tRNA

Answer 8

• DNA double stranded, mRNA and tRNA single stranded
• DNA most stable, mRNA unstable, tRNA most unstable
• DNA largest, mRNA smaller than DNA, tRNA smallest
• DNA double helix, mRNA single helix/ linear, tRNA clover shaped
• DNA has base pairing between molecules, mRNA doesn’t, tRNA has some
• DNA deoxyribose sugar, RNA ribose sugar
• DNA thymine, RNA uracil
• DNA found in nucleus, mRNA in nucleus and cytoplasm, tRNA in cytoplasm (made in nucleus)
• DNA same quantities between most cells, RNA quantity varies due to cell metabolic activity

Question 9

Describe how the structure of mRNA and tRNA are different

Answer 9

• mRNA no hydrogen bonding, tRNA has hydrogen bonding
• mRNA no base pairing, tRNA some base pairing
• mRNA linear/not folded, tRNA clover shaped/folded
• mRNA has no amino acid binding site, tRNA has amino acid binding site
• mRNA longer (more nucleotides), tRNA fixed length (less nucleotides)
• mRNA has many different kinds, tRNA only has 20

Question 10

Describe the process of transcription

Answer 10

• an enzyme (RNA polymerase) breaks hydrogen bonds to separate DNA strands
• only one DNA strand acts as a template
• RNA nucleotides are attracted to and align to complement exposed bases on template strand
• according to pairing rule (adenine -> uracil, thymine -> adenine, guamine <-> cytosine)
• RNA polymerase joins adjacent RNA nucleotides together with phosphodiester bond to form pre-mRNA
• pre-mRNA spliced to remove introns

Question 11

What happens in transcription (briefly), where does it occur?

Answer 11

• DNA converted to mRNA
• nucleus

Question 12

What happens in translation (breifly), where does it occur?

Answer 12

• mRNA converted into protein
• cytoplasm

Question 13

Describe the process of translation

Answer 13

• mRNA associates with a ribosome/attaches to mRNA
• ribosome moves to the start codon (AUG)
• tRNA carries specific amino acid
• anticodon on tRNA complementary to codon (on mRNA)
• Ribosome moves along to next codon
• / ribosome fits around 2 codon
• process repeated and amino acids join (using energy from ATP) by peptide bonds to form polypeptide