Chapter 4: DNA Structure and Gene Expression PPT4 4.4 Gene Mutations and Cancer
A gene mutation is a permanent change in DNA sequence.
• Germ-line mutations occur in sex cells and can be passed on to future
generations
• Somatic mutations occur in body cells and are not passed on to future
generations.
Both types of mutations may lead to the development of cancer.
PPT5 Causes of Mutations
• Errors in replication are mistakes made while DNA is copied. These are rare (1
mistake per billion nucleotide pairs)
• Mutagens are environmental factors, such as radiation, X rays, and some
chemicals, that cause mutations
• Transposons are DNA sequences that move within and between
chromosomes. Transposons can “jump” into another gene, causing a change in
gene expression
Figure 4.16
Transposon.
McGraw-Hill
PPT6 Effect of Mutations on Protein Activity
Gene mutations can have a range of possible effects on protein activity, from no
effect to complete inactivity or even lack of production at all.
A point mutation is a single nucleotide change. It can cause:
• No change in amino acid sequence
• A change in amino acid sequence that produces a protein that does not function
properly
• Introduction of a stop codon, which shortens the protein
PPT7
Point Mutations
Figure 4.17 Point mutations in hemoglobin
PPT8 Nonfunctional Proteins
Frameshift mutations involve one or more nucleotides being added or deleted. This
can cause a change in codons that are translated and production of a nonfunctional
protein.
• If the codons made a sentence, an example would be THE CAT ATE THE RAT; deleting the C, becomes THE ATA TET HER AT
• Just as the meaning of the sentence is scrambled, a nonfunctional protein
can have a dramatic effect on a phenotype
PPT
9 Mutations Can Cause Cancer The development of cancer involves a series of accumulating mutations, which
depend on the type of cancer. Most cancers follow a common progression.
• They begin as a benign growth of abnormal cells • They can become a malignant tumour and spread to other areas
Figure 4.18 Progression of cancer.
PPT10 Characteristics of Cancer Cells
The primary characteristics of cancer cells:
• Cancer cells are genetically unstable. Tumour cells have
multiple mutations and can have chromosomal changes.
• Cancer cells do not correctly regulate the cell cycle. The rate
of division and number of cells increases.
• Cancer cells escape the signals for cell death. Normal cell
signals for programmed cell death do not occur.
• Cancer cells can survive and proliferate elsewhere in the
body. Invasion of new tissues can occur (metastasis), which includes new blood
vessel formation (angiogenesis).
PPT14 4.5 DNA Cloning
Genetic engineering involves altering the genome, or genetic material, of an
organism. This often involves gene cloning, which is the production of copies of a
gene. Gene cloning is done to
• study what biological functions a gene is associated with
• produce large quantities of protein
• produce transgenic organisms
• help cure human diseases
PPT15 Recombinant DNA Technology
Gene cloning involves introducing a gene into a vector (often a plasmid) to produce
recombinant DNA (rDNA).
• A restriction enzyme cleaves the vector and the gene, which combine by base
pairing between the “sticky ends”
McGraw Hill
PPT16 Recombinant DNA Technology continued
• DNA ligase enzyme seals the gene and vector DNAs.
The rDNA is added to an organism such as bacteria, which
makes many copies of the gene.
PPT Gene Cloning Fig 4.19 McGraw-HillFigure 4.19
.
Cloning a human gene. Human DNA and bacterial plasmid DNA are
cleaved by a specific type of restriction enzyme. For example,
human DNA containing the insulin gene is spliced into a plasmid by
enzyme DNA ligase. Gene cloning is achieved aftera bacterium takes
up the plasmid. If the gene functions normally as expected, the
product (for example, insulin) may also be retrieved.
.
PPT18 The Polymerase Chain Reaction
The polymerase chain reaction (PCR) is a way of making billions of copies of a
segment of DNA in a test tube. PCR involves three steps that are repeated many
times in cycles.
1. Denaturation: The DNA is heated to 95oC, and it becomes single-stranded.
2. Annealing: The temperature is lowered to 50−60oC, and primers are added that
base pair to the DNA to be copied.
3. Extension: At 72oC, DNA polymerase used for PCR adds nucleotides to the ends
of the primers. Eventually both DNA strands are copied and new double-stranded
DNA forms.
PPT19 PCR is a chain reaction because the DNA is repeatedly copied.
The amount of DNA doubles with each cycle.
Fig 4.20 McGraw-Hill
PPT20 DNA Analysis
PCR has numerous applications, which includes identification of people based on
their DNA fingerprint.
• Short tandem repeat (STR) profiling identifies individuals according to how many
repeats of a DNA sequence he or she has at a particular STR locus.
Fig 4.21 McGraw-Hil