CH.6 Nucleic acids and protein synthesis Flashcards
what is a nucleotide?
a molecule consisting of a nitrogen-containing base, a pentose sugar and a phosphate group.
phosphodiester bonds join nucleotides to form a chain called polynucleotide
Name the base pairings in DNA
Adenine- Thymine
Guanine- Cytosine
Name the base pairings in RNA
Adenine- Uracil
Guanine- Cytosine
phosphodiester bond
a bond joining two nucleotides together; there are two ester bonds, one from the shared phosphate group to each of the sugars either side of it
Features of DNA
two polynucleotide chains
each chain is a right-handed helix
double helix
antiparallel chain
sugar-phosphate backbone with bases projecting at right angles
each base is attracted to the other by hydrogen bonds. This holds the chain together
complementary base pairing
2 hydrogen bonds between A-T and 3 for G-C
adenine and guanine are purines; thymine, uracil and cytosine are pyrimidines
complete turn every 10 base pairs
What is complementary base pairing?
the hydrogen bonding of A with T and of C with G in nucleic acids
Differences in hydrogen bonding between A-T and G-C
A-T 2 hydrogen bonds
G-C 3 hydrogen bonds
How many rings do purines and pyrimidines have?
purines two rings
pyrimidines three rings
distance between purine and pyrimidine is three rings ( always constant)
What is semi-conservative replication?
the method
by which a DNA molecule is copied to form
two identical molecules, each containing one
a strand from the original molecule and one newly
synthesised strand
Describe the semi-conservative replication of DNA and in what phase of the cell cycle does it occur in
S phase of cell cycle
Unwinding Process:
The two DNA strands separate through a process called ‘unzipping’ by using the enzyme Helicase.
Hydrogen bonds holding the strands together are broken.
Enzyme DNA polymerase is used for the copying process.
Attaches to single strands and adds new nucleotides one at a time.
Copying Direction Challenge:
DNA polymerase can only copy in the 5′ to 3′ direction.
Leading Strand: Copied in the same direction as unwinding.
Lagging Strand: Copied in the opposite direction, requiring backtracking.
Okazaki Fragments:
The lagging strand results in short fragments called Okazaki fragments.
Named after the biochemist who discovered them.
DNA polymerase
an enzyme that copies DNA;
it runs along the separated DNA strands lining
up one complementary nucleotide at a time
ready for joining by DNA ligase
only copies in the 5’ to 3’ direction
leading strand
during DNA replication, the
parent strand that runs in the 3′ to 5′ direction is
copied to produce the leading strand
lagging strand
during DNA replication, the
parent strand that runs in the 5′ to 3′ direction is
copied to produce the lagging strand
DNA ligase
an enzyme that catalyses the
joining together of two nucleotides with covalent
phosphodiester bonds during DNA replication
What is a gene?
a length of DNA that codes for a particular polypeptide or protein
Features of genetic code
triplet code
code is universal- each triplet codes for the same base in all living things
code has punctuations
code is redundant/ degenerate- some amino acids are coded by more than one triplet
What is transcription?
copying the genetic information
in a molecule of DNA into a complementary
strand of mRNA; a single strand of the DNA is
used as a template (this is called the template or
transcribed strand) – the enzyme responsible is
RNA polymerase
What is translation?
a stage in protein synthesis during
which a sequence of nucleotides in a molecule of
messenger RNA (mRNA) is converted (translated)
into a corresponding sequence of amino acids in
a polypeptide chain; it takes place at ribosomes
What is a codon?
sequence of three bases on an mRNA
molecule that codes for a specific amino acid or
for a stop signal
What is an anticodon?
the sequence of three unpaired bases
on a tRNA molecule that binds with a codon on
mRNA
What is gene mutation?
a change in the base sequence
in part of a DNA molecule
What is chromosome mutation?
a random and
unpredictable change in the structure or number
of chromosomes in a cell
Types of mutation
- substitution – a base is replaced by a different base ( ex. Sickle cell anaemia)
- deletion – a base is lost and not replaced
- insertion – a base is added.
What is frame-shift mutation?
a type of gene mutation
caused by insertion or deletion of one or more
nucleotides, resulting in incorrect reading of the
sequence of triplets in the genetic code due to a
shift in the reading frame
