Core Concepts (Nucleic Acids) Flashcards
What are the monomers of
nucleic acids?
Nucleotides
State the three components of
nucleotides.
● Pentose sugar
● Nitrogenous base
● Phosphate group
Draw the structure of a nucleotide.
What are the two types of organic base?
Purine and pyrimidine
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What is a purine?
● Class of organic bases
● Double ring structure
● Includes adenine (A) and guanine (G)
What is a pyrimidine?
● Class of organic bases
● Single ring structure
● Includes cytosine (C), thymine (T), uracil (U)
Describe the structure of a DNA
nucleotide.
● Deoxyribose
● Organic base (A, T, C or G)
● Phosphate group
Describe the structure of an RNA
nucleotide.
● Ribose
● Organic base (A, U, C or G)
● Phosphate group
Describe the structure of an ATP
nucleotide.
● Ribose
● Adenine
● Three phosphate groups
What is an endergonic reaction?
A non-spontaneous reaction that
requires an input of energy, e.g. ATP
formation.
What is an exergonic reaction?
A spontaneous reaction that overall
releases energy, e.g. ATP hydrolysis.
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Describe the role of ATP.
Universal energy currency. Hydrolysed to
release energy:
ATP + Water ⇌ ADP + Pi + Energy
What is complementary base pairing?
● Describes how hydrogen bonds form between
complementary purine and pyrimidine bases
● Two bonds form between A and T (or U)
● Three bonds form between G and C
Describe the structure of DNA.
● Double-stranded polymer of nucleotides twisted to form a
double helix
● Nucleotides joined by phosphodiester bonds
● Hydrogen bonds form between complementary base pairs,
A and T, C and G
● Antiparallel strands
Why are the strands of a DNA double
helix described as ‘antiparallel’?
The complementary strands run parallel but
in opposite directions, 5’ to 3’ and 3’ to 5’.
Describe the structure of RNA.
● Single-stranded polymer of nucleotides
● Nucleotides joined by phosphodiester bonds
● Hydrogen bonds form between complementary base
pairs, A and U, C and G
Name the three types of RNA
found in cells.
● Transfer RNA (tRNA)
● Messenger RNA (mRNA)
● Ribosomal RNA (rRNA)
What is the function of tRNA?
It carries specific amino acids to the
ribosomes
Describe the structure of tRNA.
● 80 nucleotides
● Single helix
● Clover leaf shape
● Anticodon on one end, amino acid binding
site on the other
What is the function of mRNA?
Carries genetic information from the
nucleus to the ribosomes for protein
synthesis.
Describe the structure of mRNA.
- 2000 nucleotides
● Single helix
● Unstable
What is the function of rRNA?
Associates with proteins in the cytoplasm
to form ribosomes.
Describe the structure of rRNA.
● 1800 to 5000 nucleotides
● Two subunits: one large, one small
What is semi-conservative replication?
The replication of DNA to produce two new
DNA molecules which both contain one new
strand and one old strand from the original
DNA molecule.
What is the role of DNA helicase in
semi-conservative replication?
It catalyses the unzipping of
double-stranded DNA into two single
strands, each of which acts as a template.
What is the role of DNA polymerase in
semi-conservative replication?
It catalyses the formation of
phosphodiester bonds between nucleotides
during the synthesis of a new DNA strand.
What is the genetic code?
The rules by which triplets in a DNA base
sequence code for the sequence of amino
acids in a polypeptide chain. The genetic code
is degenerate, universal and
non-overlapping.
Why is the genetic code described as
degenerate?
More than one triplet can code for a
particular amino acid.
Why is the genetic code described as
universal?
The same codons code for the same
amino acids in almost all organisms.
What is meant by ‘non-overlapping’?
Each base in a sequence is read once
and is only part of one triplet
Describe the ‘triplet code’ for amino
acids.
A specific sequence of three nucleotides
(known as a codon) on a molecule of DNA
or RNA codes for a particular amino acid in
protein synthesis.
What is an exon?
A region of DNA that codes for an amino
acid sequence.
