2. UNIT A: Cell Biology
Chapter 2: The Molecules of Cells
Chapter 3: Cell Structure and Function
Chapter 4: DNA Structure and Gene
Expression: Sections 4.4, 4.5
Chapter 5: Metabolism: Energy and
Enzymes
Chapter 6: Cellular Respiration
Chapter 7: Photosynthesis
3. UNIT A Chapter 4: DNA Structure and Gene Expression
Chapter 4: DNA Structure and Gene
Expression
In this chapter you will learn about the expression of an organism’s
genes, a complex series of events involving genetic and
environmental factors.
How does DNA store
information that leads to the
development, structure, and
metabolic activities of
organisms?
How are genes expressed?
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4. UNIT A Chapter 4: DNA Structure and Gene Expression
Section 4.4
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.
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5. UNIT A Chapter 4: DNA Structure and Gene Expression
Section 4.4
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.
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6. UNIT A Chapter 4: DNA Structure and Gene Expression
Section 4.4
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
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7. UNIT A Chapter 4: DNA Structure and Gene Expression
Section 4.4
Point Mutations
Figure 4.17 Point mutations in hemoglobin. The effect of a point mutation can vary.
a. Starting at the top: Normal sequence of bases in hemoglobin; next, the base change
has no effect; next, due to base change, DNA now codes for valine instead of glutamic
acid, and the result is that normal red blood cells (b) become sickle-shaped (c); next,
base change will cause DNA to code for termination and the protein will be incomplete.
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8. UNIT A Chapter 4: DNA Structure and Gene Expression
Section 4.4
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
Many reactions in cells occur in a series called a pathway. If one protein
(enzyme) is nonfunctional, it can affect the entire pathway of reactions.
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9. UNIT A Chapter 4: DNA Structure and Gene Expression
Section 4.4
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.
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10. UNIT A Chapter 4: DNA Structure and Gene Expression
Section 4.4
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).
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11. UNIT A Chapter 4: DNA Structure and Gene Expression
Section 4.4
Check Your Progress
1. Explain how gene mutations occur.
2. Distinguish between a point mutation and a
frameshift mutation.
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12. UNIT A Chapter 4: DNA Structure and Gene Expression
Section 4.4
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13. UNIT A Chapter 4: DNA Structure and Gene Expression
Section 4.4
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14. UNIT A Chapter 4: DNA Structure and Gene Expression
Section 4.5
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
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15. UNIT A Chapter 4: DNA Structure and Gene Expression
Section 4.5
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”
Many restriction enzymes
leave overhangs of
nucleotides when they cut
DNA, which are called
“sticky ends” because they
can easily base pair with
other overhangs.
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16. UNIT A Chapter 4: DNA Structure and Gene Expression
Section 4.5
Recombinant DNA Technology
• 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.
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17. UNIT A Chapter 4: DNA Structure and Gene Expression
Section 4.5
Gene Cloning
Figure 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 the enzyme DNA ligase. Gene
cloning is achieved after
a bacterium takes up the plasmid. If the gene
functions normally as expected, the product
(for example, insulin) may also be retrieved.
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18. UNIT A Chapter 4: DNA Structure and Gene Expression
Section 4.5
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.
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19. UNIT A Section 4.5
The Polymerase Chain Reaction
PCR is a chain reaction because the DNA is repeatedly
copied. The amount of DNA doubles with each cycle.
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Chapter 4: DNA Structure and Gene Expression
Figure 4.20 Polymerase chain reaction (PCR).
20. UNIT A Section 4.5
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.
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Chapter 4: DNA Structure and Gene Expression
Figure 4.21 The use of STR profiling to establish paternity.
21. UNIT A Section 4.5
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Chapter 4: DNA Structure and Gene Expression
Check Your Progress
1. Summarize the two required steps for producing
recombinant DNA.
2. Explain why STRs may be used for
identification.
22. UNIT A Section 4.5
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Chapter 4: DNA Structure and Gene Expression
23. UNIT A Section 4.5
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Chapter 4: DNA Structure and Gene Expression
Hinweis der Redaktion
Presentation title slide
Chapter opener background notes
Monozygotic twins, also known as identical twins, develop from a single fertilized egg that splits into two separate embryos. Because they come from a single zygote, they are born with the same genes. Since 1875, researchers have been studying twins to gain insight on the degree to which genes and the environment interact. Studies comparing monozygotic twins reveal that differences between twins exist because of environmental factors and the individual experiences of each twin. Twin studies have helped us understand the extent to which genetic influence is dependent on the environment. Historically, twin studies have been used in the field of behavioural genetics to distinguish between the effects of two important factors in human development: nature (genes) and nurture (environment).
Today, epigenetics is identified as a third factor that influences individual differences. Previous twin studies assumed that monozygotic twins are genetically identical. However, recent studies have shown that although monozygotic twins are born with the same genetic makeup, individual differences surface and become more apparent as the twins get older, whether or not the twins grow up in different environments or are raised together. As twins age, the differences between them increase because of the cumulative effects of environmentally induced changes to their DNA. These changes are referred to as epigenetic processes that change gene expression patterns. Younger twins have few epigenetic differences, while older twins have significantly more epigenetic differences. These epigenetic differences are a result of environmental factors, such as stress and diet, which influence how genes are expressed and behave. Some of these epigenetic factors also determine expression in subsequent generations.
gene mutation: a permanent change in the sequence of bases in DNA
Caption text
Figure 4.16 Transposon. a. A purple coding gene ordinarily codes for a purple pigment. b. A transposon “jumps” into the purple-coding gene. This mutated gene is unable to code for purple pigment and a white kernel results. c. Maize displays a variety of colours and patterns due to transposon activity.
mutagens: environmental influences causing mutations in humans
transposons: specific DNA sequences that are able to move within and between chromosomes
Caption text
Figure 4.18 Progression of cancer. A single abnormal cell begins the process, and the most aggressive cell, thereafter, becomes the one that divides the most and forms the tumour. Eventually, cancer cells gain the ability to invade underlying tissue and travel to other parts of the body, where they develop new tumours.
benign: abnormal cell growth that is not cancerous and usually does not grow larger
malignant: occurs when additional mutations cause abnormal cells to fail to respond to inhibiting signals that control the cell cycle, meaning they are cancerous and may spread
metastasis: process in which cancer cells invade new tissues and form tumours
angiogenesis: formation of new blood vessels to increase blood supplying to a growing tumour
Answers
1. Gene mutations are caused by errors in replication, by mutagens, and by transposons. Errors in replication occur when one or more bases are substituted, deleted, or inserted. Radiation and certain organic compounds can cause changes in the DNA. Transposons are pieces of DNA that can move within the chromosomes and interfere with the control of the expression of the gene, creating either too much or too little protein.
2. A point mutation only affects one amino acid and is caused by a substitution of a nucleotide base. A frameshift mutation is the insertion or deletion of one or more nucleotides in the DNA. When the mRNA containing this frameshift mutation is read at the ribosome, the sequence of codons is shifted and the message is completely different, and so is the resulting protein produced.
genetic engineering: cloning genes and using them to alter the genome of viruses and cells
genome: the complete genetic makeup of an organism
gene cloning: the production of many identical copies of a single gene
transgenic organisms: organisms with foreign DNA or genes inserted into them
vector: a piece of DNA that can be manipulated such that foreign DNA can be added to it
recombinant DNA (rDNA): contains DNA from two or more different sources
plasmids: small accessory rings of DNA from bacteria that are not part of the bacterial chromosome and are capable of self-replicating
restriction enzyme: cleaves vector DNA in order to introduce foreign DNA into it
DNA ligase: an enzyme used to seal the foreign piece of DNA into the vector DNA
polymerase chain reaction (PCR): creates billions of copies of a segment of DNA
Caption text
Figure 4.20 Polymerase chain reaction (PCR). PCR allows the production of many identical copies of DNA in a laboratory setting. Assuming you start with only one copy, you can create millions of copies with only 20 to 25 cycles. For this reason, only a tiny DNA sample is necessary for forensic genetics.
polymerase chain reaction (PCR): creates billions of copies of a segment of DNA
Caption text
Figure 4.21 The use of STR profiling to establish paternity. a. In this method, DNA fragments containing STRs are separated by gel electrophoresis. Male 1 is the father. b. Each person’s profile (only one shown) represents a unique pattern.
DNA fingerprint: a pattern of distinctive bands resulting from gel electrophoresis
short tandem repeat (STR): a type of DNA profiling used to amplify target sequences of DNA
Answers
1. The steps required for producing recombinant DNA involve a restriction enzyme to cut both the foreign DNA and the host DNA,. DNA ligase used to seal the recombined DNA strands together, and the recombinant DNA being inserted, using a vector, back into the host.
2. Short tandem repeats or STRs are repeated base pairs at a particular chromosomal location. They can be used for identification because they are unique for each individual.
