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Biology paper 1
Genetics
The Genome
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Natasha Cable
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Cards (23)
DNA
A
double-stranded
polymer of
nucleotides
, wound to form a
double helix
What are the monomers of DNA?
Nucleotides
What are DNA nucleotides made up of?
•
Common sugar
•
Phosphate
group
• One of four bases :
A
,
T
, C or
G
Names of the bases found in nucleotides
•
Adenine
•
Thymine
•
Cytosine
•
Guanine
Desc how nucleotides in to form a molecule of DNA
•
Sugar
and
phosphate
molecules join to form a
sugar-phosphate
backbone in each
DNA
strand
•
Base
connected to each
sugar
•
Complementary
base pairs joined by weak
hydrogen
bonds
Chromosome
A long, coiled molecule of DNA that carries genetic in in the form of genes
Describe the method used to extract DNA from fruit
Place the piece of fruit in a
beaker
and
crush
it
Add
detergent
and
salt
, mix
Filter
the mixture and collect the liquid in a test tube
Pour
chilled ethanol
into the test tube
DNA
precipitates
forming a
fibrous white solid
Use a
glass rod
to collect the DNA sample
Why is detergent added to the crushed fruit?
To break down
cell membranes
and release
DNA
into the solution
Why is salt added to the crushed fruit?
Salt
encourages the
precipitation
of
DNA
Explain how a gene codes for a protein
• A sequence of
three
bases in a gene forms a
triplet
• Each
triplet
codes for an
amino acid
• The
order
of amino acids determines the
structure
(i.e. how it will fold) and
function
of protein formed
Why is the ‘folding’ of amino acids important in proteins such as enzymes?
It determines the
shape
of the
active site
which must be
highly specific
to the
shape
of its
substrate
What is protein synthesis?
The
formation
of a
protein
from a
gene
What are the two stages of protein synthesis?
Transcription
and
translation
What does transcription involve?
Transcription
involves the process of converting
DNA
into
RNA
Transcription
DNA double helix
unwinds
RNA polymerase
binds to a
specific base sequence
of
non-coding DNA
in front of a
gene
and moves along the DNA strand
RNA polymerase
joins free RNA nucleotides to
complementary bases
on the
coding DNA strand
mRNA formation
complete
mRNA detaches
and
leaves
the
nucleus
Differences between mRNA and DNA
• mRNA is
single
stranded whereas DNA is
double
stranded
• mRNA uses
U
whereas DNA uses
T
Why is mRNA used in translation rather than DNA?
DNA is too
large
to leave the
nucleus
so cannot reach the
ribosome
What does translation involve?
A
ribosome
joins
amino acids
in a specific order dictated by
mRNA
to form a
protein
How is a tRNA molecule adapted to its function?
Each tRNA molecule has an
anticodon
which is specific to the codon of the
amino acid
that it carries
Mutation
A random change in the base sequence of DNA which results in genetic variants
Describe the effect of a gene mutation in coding DNA
• If a mutation changes the
amino acid sequence
,
protein structure
and
function
may change
• If a mutation does
not
change amino acid sequence, there is no effect on
protein structure
or
function
What is non-coding DNA?
The
portions
of
DNA
that do not
code
for
proteins
Describe the effect of a gene mutation in non-coding DNA
• A mutation may affect the ability of
RNA polymerase
to bind to
non-coding DNA
• This may affect
protein
production and the resulting
phenotype
of the organism