Download Mutations Notes TEK 6C

Review:
DNA, Transcription
& Translation
Structure
•
•
•
•
DNA
Code for proteins
Double Stranded Helix
Can NOT leave nucleus
Made of Sugar
(deoxyribose), Phosphate
& nitrogen base
–
–
–
–
Thymine
Adenine
Guanine
Cytosine
•
•
•
•
•
RNA
Copy of the code for
proteins
Transports code to
Ribosome
Single Stranded
Can leave nucleus
Made of Sugar (ribose),
Phosphate & nitrogen
base
–
–
–
–
Uracil
Adenine
Guanine
Cytosine
Replication
• Occurs in nucleus.
• DNA makes a copy of itself.
T
A
T
A
A
T
A
T
C G
C G
G C
G C
G C
G C
C G
C G
Transcription
• Occurs in nucleus.
• DNA makes a mRNA copy of the code.
T
A
A
A
U
T
C G
G
G C
C
G C
C
C G
G
Translation
• Occurs at Ribosome.
• mRNA binds with tRNA to build an amino
acid chain or protein.
Every 3 letters
represents one
amino acid or
codon.
Example: GUU = Valine
Summary
Mutations
• Any change in DNA sequence is called a mutation.
• Mutations can be caused by errors in replication,
transcription, cell division, or by external agents.
Mutations
• Mutations can be harmful.
– Sickle cell anemia
– Cystic fibrosis
•Mutations can be beneficial.
–Phenotypic (physical) changes
–Flower color
–Fur color
Mutations
• Mutations can occur in both types of cells:
– Body cells (muscle, skin, brain, bone etc)
– Gametes (Sex Cells – sperm or egg)
Skin Cells
Sperm Cell & Egg Cell
Mutations in body cells
• If a body cell’s DNA is changed, this mutation would
not be passed on to offspring.
• Damage to a gene may impair the function of the cell.
• When that cell divides, the new cells also will have the
same mutation.
• This can result in the cells growing and dividing
rapidly, producing cancer.
Mutations in Gametes
• Mutations that occur in the gametes or sex cells can
be passed on to the offspring.
Types of Mutations
• A point mutation is a change in a single base pair in
DNA.
THE DOG BIT THE CAT.
THE DOG BIT THE CAR.
• A change in a single nitrogenous base can change the
entire structure of a protein because a change in a
single amino acid can affect the shape of the protein.
• An example of a point mutation, is sickle-cell disease.
• Sickle-cell diseases cause the red blood cells to be
deformed. The result is that they get stuck in the
blood vessels, depriving tissues of oxygen, causing
strokes, and blood clots.
Types of Mutations
What would happen if a single nitrogenous base
(letter) is deleted?
THE DOG BIT THE CAT.
THD OGB ITT HEC AT.
• A mutation in which a single base is added or deleted
from DNA is called a frameshift mutation.
Chromosomal Alterations
• Sometimes during mitosis or meiosis chromosomes
break and then rejoin incorrectly, or just a piece
breaks off for good.
• Structural changes in
chromosomes are called
chromosomal mutations.
Deletion- part is missing
Insertion- part breaks off and attaches in the wrong
place
Inversion- part breaks off and attaches upside down
Translocation- breaks off and attaches to different
chromosome
Non-Disjunction
• Occurs during meiosis, when chromosomes fail to
separate properly.
• Normal humans have:
– 46 chromosomes
• 22 pair of Autosomes
• 1 pair of Sex
chromosomes
• Non-Disjunction:
– Too many
chromosomes?
– Too few?
– 47 or 45
chromosomes
Normal karyotype
Is this a
male or
female?
Down Syndrome
• Also called Trisomy 21
– 3 chromosomes instead of 2
Causes of Mutations
• Some mutations seem to just happen, perhaps as a
mistake in base pairing during DNA replication.
• These mutations are said to be spontaneous.
• However, many mutations are caused by factors in the
environment, such as radiation, chemicals, and even
high temperatures.
– Ex: Chernobyl explosion
• Any agent that can cause a change in DNA is called a
mutagen.