11'3 Section Objectives page 296

1

• Using the table on Pg. 292, write the amino acid
  sequence that would be made according to the
  codons on the mRNA chain.
• Why do you think this exact base sequence is
  important?

2
11.3 Section Objectives page 296
Section Objectives

• Categorize the different kinds of mutations that
  can occur in DNA.

• Compare the effects of different kinds of
  mutations on cells and organisms.

3
11.3 Section Summary 6.3 pages 296 - 301
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.

4
11.3 Section Summary 6.3 pages 296 - 301
Mutations that can be passed on

• Mutations can affect the reproductive cells of an
  organism by changing the sequence of nucleotides
  within a gene in a sperm or an egg cell.

• If this cell takes part in fertilization, the
  altered gene would become part of the genetic
  makeup of the offspring.

5
11.3 Section Summary 6.3 pages 296 - 301
Mutations in reproductive cells

• A mutation may produce a new trait or it may
  result in a protein that does not work correctly.

• Sometimes, the mutation results in a protein that
  is nonfunctional, and the embryo may not survive.

• In some rare cases a gene mutation may have
  positive effects.

6
11.3 Section Summary 6.3 pages 296 - 301
Mutations in body cells

• What happens if powerful radiation hits the DNA
  of a nonreproductive cell, a cell of the body
  such as in skin, muscle, or bone?

• If a body cells DNA is changed, this mutation
  would not be passed on to offspring.

• However, the mutation may cause problems for the
  individual.

7
11.3 Section Summary 6.3 pages 296 - 301
Mutations in body cells

• Damage to a gene may impair the function of the
  cell.

• When that cell divides, the new cells also will
  have the same mutation.

• Some mutations of DNA in body cells affect genes
  that control cell division.

• This can result in the cells growing and dividing
  rapidly, producing cancer.

8
11.3 Section Summary 6.3 pages 296 - 301
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.

9
11.3 Section Summary 6.3 pages 296 - 301
mRNA
Normal
Protein
Stop
Replace G with A
Point mutation
mRNA
Protein
Stop
10
11.3 Section Summary 6.3 pages 296 - 301

• 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.

11
11.3 Section Summary 6.3 pages 296 - 301
Types of Mutations
A point mutation takes place when a single
nitrogenous base (letter) is changed at one point.
THE DOG BIT THE CAT. THE DOG BIT THE CAR.
What would happen if a single nitrogenous base
(letter) is deleted?
THE DOG BIT THE CAT. THD OGB ITT HEC AT.
12
11.3 Section Summary 6.3 pages 296 - 301
Types of Mutations

• A mutation in which a single base is added or
  deleted from DNA is called a frameshift mutation
  because it shifts the reading of codons by one
  base.

Deletion of U
13
11.3 Section Summary 6.3 pages 296 - 301
Types of Mutations

• The new sequence with the deleted base would be
  transcribed into mRNA.
• But then, the mRNA would be out of position by
  one base.

• This mutation would cause nearly every amino acid
  in the protein after the deletion to be changed.

Deletion of U
14
11.3 Section Summary 6.3 pages 296 - 301
Frameshift mutations

• Frameshift mutations can cause severe genetic
  diseases like Cystic Fibrosis and Lou Gehrigs
  Disease.

• Lou Gehrigs Disease is a progressive
  neurological disease. Affects nerve cells used
  for voluntary muscle control

15
Lou Gehrigs Disease, or Amyotrophic Lateral
Sclerosis (ALS) is caused by a frameshift
mutation on chromosome 21.
With ALS, there is a deletion of a Cytosine on
this gene. Every other base moves down, making
all the amino acids incorrect after that.
Human Karyotype
16
Section 12.1 Summary pages 309 - 314
Cystic Fibrosis

• Cystic fibrosis (CF) is one of the most common
  fatal genetic disorders among Americans.
• It affects the lungs and digestive tract

• Due to a defective protein in the plasma
  membrane, cystic fibrosis results in the
  formation and accumulation of thick mucus in the
  lungs and digestive tract.

17
Cystic Fibrosis is caused by a frameshift
mutation on chromosome 7. Three nitrogenous bases
are deleted to cause this mutation in the amino
acid sequence.
18
11.3 Section Summary 6.3 pages 296 - 301
Chromosomal Alterations

• Changes may occur in chromosomes as well as in
  genes.

• 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.

19
11.3 Section Summary 6.3 pages 296 - 301
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.

• Any agent that can cause a change in DNA is
  called a mutagen.

20
11.3 Section Summary 6.3 pages 296 - 301
Repairing DNA

• Enzymes proofread the DNA and replace incorrect
  nucleotides with correct nucleotides.

• These repair mechanisms work extremely well, but
  they are not perfect.

• The greater the exposure to a mutagen such as UV
  light, the more likely is the chance that a
  mistake will not be corrected.

21
Section 3 Check
Question 1
Any change in DNA sequences is called a
_______.
A. replication
B. mutation
C. transcription
D. translation
The answer is B.
22
Section 3 Check
Question 2
Which is more serious, a point mutation or a
frameshift mutation? Why?
Answer
A frameshift mutation is more serious than a
point mutation because it disrupts more codons
than a point mutation.
23
Section 3 Check
Question 3
Why are chromosomal mutations rarely passed
on to the next generation?
Answer
Few chromosomal changes are passed on to the next
generation because the zygote usually dies. If
the zygote survives, it is often sterile and
incapable of producing offspring.