6. Nucleic acids and protein synthesis

Question 1

describe the structure of nucleotides

Answer 1

a nitrogenous base- ATCG/AUCG
a five-carbon sugar (ribose or deoxyribose) RNA/DNA
a phosphate group.

Question 2

structure of ATP

Answer 2

a nitrogenous base (adenine), a ribose sugar, and three phosphate groups

Question 2

base structures

Answer 2

bases adenine and guanine are purines with a double ring structure

bases cytosine, thymine and uracil are pyrimidines with a single ring structure

Question 2

structure of a DNA molecule

Answer 2

a double helix

• the importance of complementary base pairing between the 5′ to 3′ strand and the 3′ to 5′ strand (antiparallel strands)
• differences in hydrogen bonding between C–G (3 H bonds) and A–T( 2 H bonds) base pairs-
• linking of nucleotides by phosphodiester bonds

Question 3

describe the structure of an RNA molecule, using the example
of messenger RNA (mRNA)

Answer 3

single-stranded RNA molecule, carrying genetic information from DNA to ribosomes for protein synthesis.

nucleotide-
nitrogeneous base- AUCG
phosphate group
5 carbon ribose sugar- OH group on carbon 2

Question 3

semi-conservative replication of DNA

Answer 3

during the S phase of the cell cycle

• the roles of DNA polymerase and DNA ligase
• the differences between leading strand and lagging strand replication as a consequence of DNA polymerase adding nucleotides only in a 5′ to 3′ direction

Answer 4

a polypeptide is coded for by a gene a gene is a sequence of nucleotides that forms part of a DNA molecule.

Question 5

principle of the universal genetic code

Answer 5

different triplets of DNA bases either code for specific amino acids or correspond to start and stop codons

Question 6

translation

Question 7

transcription

Question 8

strands used in transcription

Answer 8

the strand of a DNA molecule that is used in transcription is called the transcribed or template strand and
that the other strand is called the non-transcribed strand

Question 9

after transcription, how does RNA molecule turn into mRNA?

Answer 9

in eukaryotes, the RNA molecule formed following transcription (primary transcript) is modified by the removal of non-coding sequences (introns) and the joining
together of coding sequences (exons) to form mRNA.

Question 10

what is a gene mutation

Answer 10

a gene mutation is a change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide

Question 11

how does gene mutation take place?

how each of these types of mutation may affect the polypeptide produced

Answer 11

a gene mutation is a result of substitution or deletion or insertion of nucleotides in DNA.

substitution-
insertion-
deletion- frameshift