Nucleic acids

Question 1

Bases in DNA

Answer 1

Adenine, Thymine, Cytosine, Guanine

Question 2

RNA

Answer 2

Ribonucleic acid. Single stranded (usually) polynucleotide. Sugar is ribose. 3 forms exist

Question 3

Bases in RNA

Answer 3

Adenine, Uracil, Cytosine, Guanine

Question 4

Complementary base pairings

Answer 4

Adenine-Thymine/Uracil (2 H-bonds) and Cytosine-Guanine (3 H-bonds)

Question 5

Purine bases

Answer 5

Adenine, Guanine. Larger than pyrimidines

Question 6

Pyrimidine bases

Answer 6

Thymine, Uracil, Cytosine. Smaller than purines

Question 7

Nucleotide

Answer 7

The monomer of all nucleic acids. Each nucleotide is formed by bonding together a phosphate group, a sugar molecule and a nitrogenous base

Question 8

DNA replication

Answer 8

• Semi-conservative, as creates 2 identical DNA molecules, each with one original strand and one new strand
• Double helix untwists
• Double helix unzips, breaking hydrogen bonds between bases with the help of DNA helicase, exposing bases
• Free DNA nucleotides are hydrogen bonded onto the exposed bases, according to complementary base pairing rules (A-T, C-G). Occurs with help of DNA polymerase
• Covalent bonds form between phosphate group on one nucleotide and the sugar group on the next with the help of DNA ligase, sealing the backbone

Question 9

Gene

Answer 9

Length of DNA (sequence of polypeptides) that codes for one (or more) polypeptides. Each gene occupies a specific place (locus) on a chromosome. Different versions of the same gene are called alleles

Question 10

2 steps in protein synthesis

Answer 10

Transcription, translation

Question 11

Transcription in protein synthesis

Answer 11

• DNA double helix unzips, exposing bases
• RNA nucleotides attach to exposed bases, using rules of complementary base pairing (T-A, A-U, C-G, G-C)
• RNA polymerase helps this process
• mRNA molecules exits nucleus via nuclear pores and enters cytoplasm

Question 12

Translation in protein synthesis

Answer 12

• mRNA molecule attaches to a ribosome in cytoplasm
• mRNA is read in triplets of bases called a codon
• anticodon (3 bases on a tRNA molecule) attaches on to codon
• peptide bonds are formed between the amino acids attached to the tRNA, creating a polypeptide chain

Question 13

mRNA

Answer 13

Made as a strand complementary to one strand of a DNA molecule (the template strand), so it is therefore a copy of the coding strand. It carries the information held in the DNA out of the nucleus and into the cytoplasm to synthesise a protein, as the DNA molecule is too large to leave

Question 14

tRNA

Answer 14

Carries amino acids to the ribosomes where they are bonded together to form polypeptides. Around 80 nucleotides long. Chain folds up and is stabilised by hydrogen bonds as complementary bases come near each other. Structure usually shown simplified as a hairpin

Question 15

rRNA

Answer 15

With proteins, forms ribosomes. Accounts for around 80% of total RNA in the cell

Question 16

DNA

Answer 16

Deoxyribonucleic acid. Double stranded (usually) polynucleotide, strands run in antiparallel. Strands twist into a double helix structure. Sugar is deoxyribose.