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GCSE level biology exam genetics revision notes:
Genome 2.5
What are
the consequences of mutations in DNA?
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Sub-index of biology notes on genetic variation, and the causes, formation and
consequences of mutations
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(2.5) Examples of
the consequences of mutations in DNA?
Important reminders:
(i) Enzymes are proteins. They catalyse most reactions
in organisms.
They have a specific shape and molecular structure that
enables them to catalyse specific reactions.
If the enzyme protein molecule is not correctly
synthesised, then it cannot perform its catalytic role in biochemistry.
This is illustrated with the diagram and notes below.
The correct enzyme protein
might not be formed and can have serious consequences!
with
reference to the above diagram A to C
A The protein structure of the enzyme is
correctly formed form correctly coded DNA i.e. no mutations have had
an adverse effect. The amino acid sequence correct and so the
protein coils into its correct 3D structure and the active site can
accept the substrate molecule.
B The chemical change can take place because the protein structure
of the active site is the correct 3D shape to accept the substrate
molecule which 'docks in' - the 'key and lock' mechanism.
C
One or more mutations has caused a change in the amino acid
sequence, leading to a change in protein shape at the active site,
so the substrate molecule cannot 'dock' in and be chemically changed
by the enzyme.
Note that all the rest of the enzyme structure is correct, and even if
not due to a mutation affecting the amino acid sequence, it might not affect the
active site. One reason why mutations do not always have a
detrimental effect on the protein-enzyme structure and function.
(ii)
If a mutation produces a change in the triplet
codes for amino acids then the final protein formed may have a different
structure and a non/different function compared to the one that was supposed to have been formed
(this was explained in section (a) above.
The protein produced is unlikely to be able to
perform the function that was intended from the DNA code.
The protein might do something different or may be
incapable of doing anything.
A single mutation changing the function of a single
protein molecule can have a significant effect on the phenotype if the
genotype is incorrect.
Note that most mutations have no effect on an
organism's phenotypes.
Some mutations can have a small effect, but
there are rare mutations that can produce a new phenotype in a
species - see
evolution.
Examples
of mutations (more
details on other pages):
The
genetic disorder cystic fibrosis is caused by
the deletion of three bases with a massive detrimental effect on the
phenotype.
The 'damaged' gene codes for a protein that controls the
movement of salt and water in and out of cells -semi-permeable membrane
control. Unfortunately, the protein produced by the cystic fibrosis
variant doesn't work correctly. The result in the individual is excess
mucous production in the lungs and digestive systems and this causes
difficulty in breathing and digesting food.
Some mutations have a slight effect on protein
function and have a relatively small effect on the phenotype - I presume
the protein molecule is sufficiently well formed enough to do its
function, but perhaps not perfectly.
Mutations of coding DNA do not necessarily change
the amino acid sequence of a protein.
Here, such mutations have no
effect on the phenotype i.e. no effect on the characteristics of an
organism.
This is in sharp contrast to the sufferers of cystic fibrosis.
Be able to demonstrate an understanding of how gene
mutations change the DNA base sequence and that mutations can be:
(i)
harmful - causing genetic disorders like
cystic fibrosis, Downe syndrome, haemophilia and colour blindness.
(ii)
beneficial
- the gene expression
produces an enhanced feature that makes that organism more able to survive,
this is partly responsible for driving the evolution of more successful
species, but not always to our benefit! e.g. bacteria genes are quite
susceptible to mutations and some are becoming very resistant to antibiotics
as their DNA subtly changes!
(iii)
or neither ('neutral') - any faults
from DNA mutations do not affect the organisms existence i.e. protein
functions are not affected, no advantage is gained and no disadvantage
either.
For more details see
Introduction to the inheritance of characteristics and
genetic diagrams (including Punnett squares) including technical terms, Mendel's work and inherited
genetic disorders, genetic testing
Key biology points
Source of information is based on
the syllabus-specifications for students taking the AQA GCSE, Edexcel GCSE and OCR
GCSE level biology examinations (~US grades 9-10).
Key
points and more examples of the consequences of mutations
Consequences of
Mutations and Their Importance in Human Genetics
Mutations are changes
in the DNA sequence that can have various effects on an organism.
Some mutations are
neutral, while others can lead to diseases or beneficial traits.
Understanding these
consequences helps scientists study genetics, evolution, and medical
conditions.
1.
Harmful
Mutations
Harmful mutations can
disrupt normal biological processes, leading to genetic disorders or
increased disease susceptibility.
Examples of
Harmful Mutations:
-
Cystic
Fibrosis: Caused by a
deletion mutation in the CFTR gene, leading to thick mucus in the
lungs and digestive system.
-
Sickle Cell
Anemia: A substitution
mutation in the hemoglobin gene changes the shape of red blood
cells, causing poor oxygen transport and blockages in blood vessels.
-
Huntington’s
Disease: A
trinucleotide repeat expansion in the HTT gene leads to progressive
brain degeneration.
-
Cancer:
Mutations in tumor suppressor genes or oncogenes can cause
uncontrolled cell growth.
2.
Neutral
Mutations
Neutral mutations have no
immediate effect on an organism's survival or function. They may persist
in a population without consequences.
Examples of
Neutral Mutations:
-
Silent
mutations (e.g., a
change in a DNA base that doesn’t alter the protein produced).
-
Genetic
variants that do not
affect health but contribute to individual differences (e.g., SNPs
that influence hair or eye color).
-
Some
evolutionary changes
that may become significant over generations.
3.
Beneficial
Mutations
Beneficial mutations
enhance survival, adaptation, or resistance to diseases, playing a
key role in evolution.
Examples of
Beneficial Mutations:
-
Lactose
Tolerance: A mutation
in the LCT gene allows some populations to digest milk into
adulthood.
-
Malaria
Resistance: The sickle
cell trait (heterozygous form) provides resistance against malaria.
-
Increased Bone
Density: Mutations in
the LRP5 gene strengthen bones, reducing fracture risk.
-
HIV
Resistance: A mutation
in the CCR5 gene can prevent HIV from entering white blood cells.
Importance in
Human Genetics
Studying mutations
helps researchers and doctors in multiple ways:
-
Disease
Diagnosis and Treatment:
Identifying mutations linked to genetic disorders enables better
screening and medical interventions.
-
Evolutionary
Biology: Mutations
drive adaptation and genetic diversity, helping species survive
environmental changes.
-
Gene Therapy:
Scientists explore ways to correct harmful mutations using genetic
engineering techniques.
-
Personalized
Medicine:
Understanding genetic mutations allows tailored treatments based on
individual DNA profiles.
Mutations shape life
and influence health, making their study essential for medical
advancements and evolutionary research.
Summary of learning objectives and key words or phrases
Know the consequences of mutations in DNA which may not
allow a
correct enzyme protein to be made,
Know that mutations can cause genetic disorders because
of a faulty mutated protein mutated and this may have serious consequences
e.g. the wrong phenotype characteristic from a faulty genotype.
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