1.4 Nucleic Acids Flashcards
What are the monomers of nucleic acids?
nucleotides
State the three components of
nucleotides
● Pentose sugar
● Organic base
● Phosphate group
What are the two types of organic base?
purine and prymidine
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.
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
what is an intron?
A non-coding sequence of DNA that is
found between exons
Compare eukaryotic and prokaryotic genes.
● Eukaryotic genes are discontinuous with
non-coding introns and coding exons
● Prokaryotic genes are continuous with
coding sequences only
what is protein synthesis?
The formation of proteins from amino
acids. There are two stages:
transcription and translation.
define transcription?
● First stage of protein synthesis
● The formation of pre-mRNA in eukaryotes and mRNA in prokaryotes from a section of the template strand of DNA
outline the process of transcription
- DNA helicase unwinds section of DNA, breaking hydrogen bonds between the DNA strands. The antisense strand acts as a template.
- RNA polymerase binds to the promoter region on a gene
- Free RNA nucleotides align next to their complementary bases
- RNA polymerase joins adjacent RNA nucleotides, forming phosphodiester
bonds - RNA polymerase reaches stop codon and detaches. mRNA complete.
Describe post-transcriptional
modification.
Splicing removes introns from pre-mRNA
in eukaryotic cells.
define translation
● Second stage of protein synthesis
● Takes place in the ribosomes
● mRNA used as a template for the attachment of tRNA molecules with complementary anticodons. Amino acids
carried on adjacent tRNA molecules are joined to form a polypeptide chain
outline the process of translation
- mRNA attaches to groove between subunits of ribosome
- Ribosome moves along mRNA until ‘start’ codon reached
- Amino acid-tRNA complex anticodon attaches to complementary mRNA
codon via hydrogen bonding. Another complex binds - Peptide bond forms between adjacent amino acids in the complexes
- Ribosome moves along one codon and release empty tRNA. Process continues to form polypeptide chain until ‘stop’ codon is reached
The theory that each gene encodes a
single protein.
The theory that each gene encodes a
single protein.
What happens to the polypeptide after
translation?
● Further modified by adding
carbohydrates, lipids or phosphates
● Different polypeptides may be combined
Describe how DNA can be purified by precipitation.
● Add ethanol and a salt to aqueous solution. Nucleic acids precipitate out of solution
● Centrifuge to obtain pellet of nucleic acid
● Wash pellet with ethanol and centrifuge again
