DNA : The Genetic Material

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DNA The Genetic Material

• Chapter 9
• By Mrs. Fleck

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Identifying the Genetic MaterialSection 1

• Transformation- is a change in genotype caused
  when cells take up foreign genetic material.
• Griffiths experiments discovered transformation.
• -caused harmless bacteria (even dead) to
  become deadly.
• Vaccine- is a substance that is prepared from
  killed or weakened disease causing agents.
• Virulent- able to cause disease
• Averys experiments- conclude -that DNA is the
  material responsible for transformation.
• -Bacteriophage is a virus that infects bacteria
• Hershey Chase Experiments- concluded DNA ,
  rather than proteins , is the heredity material .

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Section 11.1 Summary pages 281 - 287
DNA as the genetic material

• Hershey and Chase labeled the virus DNA with a
  radioactive isotope and the virus protein with a
  different isotope.

• By following the infection of bacterial cells by
  the labeled viruses, they demonstrated that DNA,
  rather than protein, entered the cells and caused
  the bacteria to produce new viruses.

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Section 11.1 Summary pages 281 - 287
What is DNA?

• All actions, such as eating, running, and even
  thinking, depend on proteins called enzymes.

• Enzymes are critical for an organisms function
  because they control the chemical reactions
  needed for life.

• Within the structure of DNA is the information
  for lifethe complete instructions for
  manufacturing all the proteins for an organism.

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Section 11.1 Summary pages 281 - 287
The structure of nucleotides

• DNA is a polymer made of repeating subunits
  called nucleotides.

Nitrogenous base
Phosphate group
Sugar (deoxyribose)

• Nucleotides have three parts a simple sugar, a
  phosphate group, and a nitrogenous base.

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Section 11.1 Summary pages 281 - 287
The structure of nucleotides

• The simple sugar in DNA, called deoxyribose (dee
  ahk sih RI bos), gives DNA its namedeoxyribonucle
  ic acid.

• The phosphate group is composed of one atom of
  phosphorus surrounded by four oxygen atoms.

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Section 11.1 Summary pages 281 - 287
The structure of nucleotides

• A nitrogenous base is a carbon ring structure
  that contains one or more atoms of nitrogen.

• In DNA, there are four possible nitrogenous
  bases adenine (A), guanine (G) are
  (Purines)double ring of carbon and nitrogen.
• Cytosine (C), and thymine (T) are
  (Pyrimidines)single ring

Cytosine (C)
Guanine (G)
Thymine (T)
Adenine (A)
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Section 11.1 Summary pages 281 - 287
The structure of nucleotides

• Thus, in DNA there are four possible nucleotides,
  each containing one of these four bases.
• Base Pairing
• A-T (This pairing allows DNA to make
• G-C a perfect copy of itself.)
• These pairs are held together by two weak
  hydrogen bonds. (Complementary base pairs)
• Each base is held to the backbone with a stronger
  bond. The strong bond ensures that its sequence
  will not get mixed up.

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Section 11.1 Summary pages 281 - 287
The structure of nucleotides

• Nucleotides join together to form long chains,
  with the phosphate group of one nucleotide
  bonding to the deoxyribose sugar of an adjacent
  nucleotide.

• The phosphate groups and deoxyribose molecules
  form the backbone of the chain, and the
  nitrogenous bases stick out like the teeth of a
  zipper.

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Section 11.1 Summary pages 281 - 287
The structure of nucleotides

• In DNA, the amount of adenine is always equal to
  the amount of thymine, and the amount of guanine
  is always equal to the amount of cytosine.

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Section 11.1 Summary pages 281 - 287
The structure of DNA

• In 1953, Watson and Crick proposed that DNA is
  made of two chains of nucleotides held together
  by nitrogenous bases.

• Watson and Crick also proposed that DNA is shaped
  like a long zipper that is twisted into a coil
  like a spring.

• Because DNA is composed of two strands twisted
  together, its shape is called double helix.

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Section 11.1 Summary pages 281 - 287
Replication of DNA

• Before a cell can divide by mitosis or meiosis,
  it must first make a copy of its chromosomes.

• The DNA in the chromosomes is copied in a process
  called DNA replication.
• Before DNA can replicate it must uncoil.

• Without DNA replication, new cells would have
  only half the DNA of their parents.

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Section 11.1 Summary pages 281 - 287
Replication of DNA
Click this image to view movie (ch11)
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Section 11.1 Summary pages 281 - 287
DNA
Replication
Replication of DNA
Replication
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Section 11.1 Summary pages 281 - 287
Copying DNA

• DNA is copied during interphase prior to mitosis
  and meiosis.

• It is important that the new copies are exactly
  like the original molecules.

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Roles of Enzymes

• 1. Chemical bonds connecting the bases break due
  to enzymes called helicases. These move along the
  chain and the chain unwinds and separates.
• 2. The DNA molecule separates into 2
  complementary halves. (The areas where the double
  helix separates are called replication forks.)
• 3. Free floating nucleotides join with the
  complementary nucleotides on the single strands.
• 4. DNA polymerase (enzyme) binds to the separated
  chain and links the nucleotide back into a long
  strand.
• DNA polymerase also has a proof reading role- in
  the event of a mismatched nucleotide it can
  replace it with a correct one.

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The Rate of Replication

• Each human chromosome is replicated in about
  100sections that are 100,000 nucleotides long,
  each section with its own starting point.
• Replication forks work in concert, so that an
  entire human chromosome can be replicated in
  about 8 hours.
• Replication forks tend to speed up replication.
• Replication forks are more plentiful in
  eukaryotes (100) than in prokaryotes. (2)

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Section 11.1 Summary pages 281 - 287
Copying DNA
New DNA molecule
Original DNA Strand
Free Nucleotides
New DNA molecule
New DNA Strand
Original DNA Strand
Original DNA
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Section 11.1 Summary pages 281 - 287
The importance of nucleotide sequences
The sequence of nucleotides forms the unique
genetic information of an organism. The closer
the relationship is between two organisms, the
more similar their DNA nucleotide sequences will
be.
Chromosome
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How Proteins are Made

• Chapter 10
• Mrs. Fleck

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Section 11.2 Summary pages 288 - 295
Genes and Proteins

• The sequence of nucleotides in DNA contain
  information.

• This information is put to work through the
  production of proteins.

• Proteins fold into complex, three-
  dimensional shapes to become key cell
  structures and regulators of cell functions.

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Section 11.2 Summary pages 288 - 295
Genes and Proteins

• Some proteins become important structures, such
  as the filaments in muscle tissue.

• Other proteins, such as enzymes, control
  chemical reactions that perform key life
  functionsbreaking down glucose molecules in
  cellular respiration, digesting food, or making
  spindle fibers during mitosis.

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Section 11.2 Summary page 288 - 295
Genes and Proteins

• In fact, enzymes control all the chemical
  reactions of an organism.

• Thus, by encoding the instructions for making
  proteins, DNA controls cells.

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Section 11.2 Summary page 2888- 295
Genes and Proteins

• You learned earlier that proteins are
  polymers of amino acids.

• The sequence of nucleotides in each gene
  contains information for assembling the
  string of amino acids that make up a single
  protein.

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Section 11.2 Summary pages 288 - 295
RNA

• RNA like DNA, is a nucleic acid. RNA structure
  differs from DNA structure in four ways.

• First, RNA is single strandedit looks like
  one-half of a zipper whereas DNA is double
  stranded.

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Section 11.2 Summary pages 288 - 295
RNA
Ribose

• The sugar in RNA is ribose DNAs sugar is
  deoxyribose.
• RNA is Mobile and DNA is not mobile.

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Section 11.2 Summary pages 288 - 295
RNA

• Both DNA and RNA contain four nitrogenous bases,
  but rather than thymine, RNA contains a similar
  base called uracil (U).

• Uracil forms a base pair with adenine in RNA,
  just as thymine does in DNA.

Uracil
Hydrogen bonds
Adenine
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Section 11.2 Summary pages 288 - 295
RNA

• DNA provides workers with the instructions for
  making the proteins, and workers build the
  proteins.

• The workers for protein synthesis are RNA
  molecules.

• They take from DNA the instructions on how the
  protein should be assembled, thenamino acid by
  amino acidthey assemble the protein.
• The entire process by which proteins are made is
  called Gene Expression

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Section 11.2 Summary pages 288 - 295
RNA

• There are three types of RNA that help build
  proteins. (mRNA, tRNA, rRNA)

• Messenger RNA (mRNA), brings instructions from
  DNA in the nucleus to the cells factory floor,
  the cytoplasm.

• On the factory floor, mRNA moves to the assembly
  line, a ribosome.

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Section 11.2 Summary pages 288 - 295
RNA

• The ribosome, made of ribosomal RNA (rRNA), binds
  to the mRNA and uses the instructions to assemble
  the amino acids in the correct order.

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Section 11.2 Summary pages 288 - 295
Transcription
A
DNA strand
RNA strand
RNA strand
C
B
DNA strand
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Section 11.2 Summary pages 288 - 295
Transcription

• In the nucleus, enzymes make an RNA copy of a
  portion of a DNA strand in a process called
  transcription.

Click image to view movie (ch11)
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Section 11.2 Summary pages 288 - 295
Transcription

• The main difference between transcription and DNA
  replication is that transcription results in the
  formation of one single-stranded RNA molecule
  rather than a double-stranded DNA molecule.

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Section 11.2 Summary pages 288 - 295
RNA

• Transfer RNA (tRNA) is the supplier. Transfer
  RNA delivers amino acids to the ribosome to be
  assembled into a protein.

Click image to view movie
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Section 11.2 Summary pages 288 - 295
The Genetic Code

• The nucleotide sequence transcribed from DNA to a
  strand of messenger RNA acts as a genetic
  message, the complete information for the
  building of a protein.

• As you know, proteins contain chains of amino
  acids. You could say that the language of
  proteins uses an alphabet of amino acids.

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The Genetic Code

• A code is needed to convert the language of mRNA
  into the language of proteins.

• Biochemists began to crack the genetic code when
  they discovered that a group of three nitrogenous
  bases in mRNA code for one amino acid. Each group
  is known as a codon.

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Section 11.2 Summary pages 288 - 295
The Genetic Code
The Messenger RNA Genetic Code
First Letter
Third Letter
Second Letter
U
A
C
G
U
U
Phenylalanine (UUU)
Serine (UCU)
Tyrosine (UAU)
Cysteine (UGU)
C
Cysteine (UGC)
Phenylalanine (UUC)
Serine (UCC)
Tyrosine (UAC)
A
Stop (UGA)
Serine (UCA)
Stop (UAA)
Leucine (UUA)
G
Leucine (UUG)
Serine (UCG)
Stop (UAG)
Tryptophan (UGG)
U
C
Arginine (CGU)
Leucine (CUU)
Proline (CCU)
Histadine (CAU)
Arginine (CGC)
C
Proline (CCC)
Leucine (CUC)
Histadine (CAC)
A
Proline (CCA)
Arginine (CGA)
Leucine (CUA)
Glutamine (CAA)
Arginine (CGG)
G
Glutamine (CAG)
Proline (CCG)
Leucine (CUG)
A
U
Isoleucine (AUU)
Threonine (ACU)
Asparagine (AAU)
Serine (AGU)
C
Serine (AGC)
Asparagine (AAC)
Isoleucine (AUC)
Threonine (ACC)
A
Arginine (AGA)
Isoleucine (AUA)
Threonine (ACA)
Lysine (AAA)
G
Arginine (AGG)
MethionineStart (AUG)
Threonine (ACG)
Lysine (AAG)
G
U
Glycine (GGU)
Valine (GUU)
Alanine (GCU)
Aspartate (GAU)
C
Valine (GUC)
Aspartate (GAC)
Glycine (GGC)
Glycine (GGC)
Alanine (GCC)
A
Glycine (GGA)
Alanine (GCA)
Glutamate (GAA)
Valine (GUA)
Glutamate (GAG)
Glycine (GGG)
G
Alanine (GCG)
Valine (GUG)
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Section 11.2 Summary pages 288 - 295
The Genetic Code

• All organisms use the same genetic code.

• This provides evidence that all life on Earth
  evolved from a common origin.

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Section 11.2 Summary pages 288 - 295
The Genetic Code

• Some codons do not code for amino acids they
  provide instructions for making the protein.

• More than one codon can code for the same amino
  acid.

• However, for any one codon, there can be only one
  amino acid.

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Section 11.2 Summary pages 288 - 295
Translation From mRNA to Protein

• The process of converting the information in a
  sequence of nitrogenous bases in mRNA into a
  sequence of amino acids in protein is known as
  translation.

• Translation takes place at the ribosomes in the
  cytoplasm.

• In prokaryotic cells, which have no nucleus, the
  mRNA is made in the cytoplasm.

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Section 11.2 Summary pages 288 - 295
Translation From mRNA to Protein

• In eukaryotic cells, mRNA is made in the nucleus
  and travels to the cytoplasm.

• In cytoplasm, a ribosome attaches to the strand
  of mRNA like a clothespin clamped onto a
  clothesline.

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Section 11.2 Summary pages 288 - 295
The role of transfer RNA

• For proteins to be built, the 20 different amino
  acids dissolved in the cytoplasm must be brought
  to the ribosomes.

• This is the role of transfer RNA.

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Section 11.2 Summary pages 288 - 295
The role of transfer RNA
Amino acid

• Each tRNA molecule attaches to only one type of
  amino acid.

Chain of RNA nucleotides
Transfer RNA molecule
Anticondon
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Section 11.2 Summary pages 288 - 295
The role of transfer RNA

• As translation begins, a ribosome attaches to the
  starting end of the mRNA strand. Then, tRNA
  molecules, each carrying a specific amino acid,
  approach the ribosome.

• When a tRNA anticodon pairs with the first mRNA
  codon, the two molecules temporarily join
  together.

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Section 11.2 Summary pages 288 - 295
The role of transfer RNA

• Usually, the first codon on mRNA is AUG, which
  codes for the amino acid methionine.

• AUG signals the start of protein synthesis.

• When this signal is given, the ribosome slides
  along the mRNA to the next codon.

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Section 11.2 Summary pages 288 - 295
The role of transfer RNA
Ribosome
mRNA codon
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Section 11.2 Summary pages 288 - 295
The role of transfer RNA
Methionine
tRNA anticodon
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Section 11.2 Summary pages 288 - 295
The role of transfer RNA

• A new tRNA molecule carrying an amino acid pairs
  with the second mRNA codon.

Alanine
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Section 11.2 Summary pages 288- 295
The role of transfer RNA

• The amino acids are joined when a peptide bond is
  formed between them.

Methionine
Alanine
Peptide bond
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Section 11.2 Summary pages 288 - 295
The role of transfer RNA

• A chain of amino acids is formed until the stop
  codon is reached on the mRNA strand.

Stop codon
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Section 10.2Gene Regulation and Structure

• Both prokaryotic and Eukaryotic cells are able to
  regulate which genes are expressed and which are
  not, depending on the cells needs.
• Gene regulation is necessary in living organisms
  to avoid wasting their energy on making proteins
  that are not needed.

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Turning Genes On and Off

• Operator piece of DNA that serves as an on and
  off switch for transcription. (it aids in
  shielding the RNA polymerase binding site of a
  specific gene.
• Operon a group of genes that code for enzymes
  involved in the same function, their promoter
  site, and the operator that controls them.
• The operon that controls the metabolism of
  lactose is called the lac operon.
• The lac operon- enables a bacterium to build the
  proteins needed for lactose metabolism only when
  lactose is present.
• Repressor a protein that binds to an operator
  and inhibits transcription. (Blocks movement of
  RNA polymerase)

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Gene Regulation Occurrence

• Is more complex in Eukaryotes
• Can occur before, during or after transcription.
• Can occur after translation.

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Section 11.2 Summary pages 288 - 295
RNA Processing

• Not all the nucleotides in the DNA of eukaryotic
  cells carry instructionsor codefor making
  proteins.

• Genes usually contain many long noncoding
  nucleotide sequences, called introns, that are
  scattered among the coding sequences.

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Section 11.2 Summary pages 288 - 295
RNA Processing

• Regions that contain information are called exons
  because they are expressed. (or translated)

• When mRNA is transcribed from DNA, both introns
  and exons are copied.

• The introns must be removed from the mRNA before
  it can function to make a protein.

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Section 11.2 Summary pages 288 - 295
RNA Processing

• Enzymes in the nucleus cut out the intron
  segments and paste the mRNA back together.

• The mRNA then leaves the nucleus and travels to
  the ribosome.
• Many Biologists think this organization of genes
  adds evolutionary flexibility

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11.3 Section Summary 6.3 pages 296 - 301
Mutations

• Organisms have evolved many ways to protect their
  DNA from changes.

• In spite of these mechanisms, however, changes in
  the DNA occasionally do occur.

• Any change in DNA sequence is called a mutation.

• Mutations can be caused by errors in replication,
  transcription, cell division, or by external
  agents.

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

• 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.

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

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

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

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

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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.

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11.3 Section Summary 6.3 pages 296 - 301
The effects of point mutations

• A point mutation is a change in a single base
  pair in DNA.

• 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.

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11.3 Section Summary 6.3 pages 296 - 301
The effects of point mutations
mRNA
Normal
Protein
Stop
Replace G with A
Point mutation
mRNA
Protein
Stop
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11.3 Section Summary 6.3 pages 296 - 301
Frameshift mutations

• What would happen if a single base were lost from
  a DNA strand?

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

• As a result, every codon after the deleted base
  would be different.

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11.3 Section Summary 6.3 pages 296 - 301
Frame shift mutations

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

• 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.

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11.3 Section Summary 6.3 pages 296 - 301
Frameshift mutations
Deletion of U
mRNA
Frameshift mutation
Protein
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11.3 Section Summary 6.3 pages 296 - 301
Chromosomal Alterations

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

• Alterations to chromosomes may occur in a variety
  of ways.

• Structural changes in chromosomes are called
  chromosomal mutations.

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11.3 Section Summary 6.3 pages 296 - 301
Chromosomal Alterations

• Chromosomal mutations occur in all living
  organisms, but they are especially common in
  plants.

• Few chromosomal mutations are passed on to the
  next generation because the zygote usually dies.

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11.3 Section Summary 6.3 pages 296 - 301
Chromosomal Alterations

• In cases where the zygote lives and develops, the
  mature organism is often sterile and thus
  incapable of producing offspring.

• When a part of a chromosome is left out, a
  deletion occurs.

A B C D E F G H
A B C E F G H
Deletion
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11.3 Section Summary 6.3 pages 296 - 301
Chromosomal Alterations

• When part of a chromatid breaks off and attaches
  to its sister chromatid, an insertion occurs.

• The result is a duplication of genes on the same
  chromosome.

A B C B C D E F G H
A B C D E F G H
Insertion
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11.3 Section Summary 6.3 pages 296 - 301
Chromosomal Alterations

• When part of one chromosome breaks off and is
  added to a different chromosome, a translocation
  occurs.

G
E
H
F
A
B
F
C
G
D
E
D
C
B
X
A
W
H
X
Z
W
Y
Y
Z
Translocation
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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.

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11.3 Section Summary 6.3 pages 296 - 301
Causes of Mutations

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

• Mutagens include radiation, chemicals, and even
  high temperatures.

• Forms of radiation, such as X rays, cosmic rays,
  ultraviolet light, and nuclear radiation, are
  dangerous mutagens because the energy they
  contain can damage or break apart DNA.

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11.3 Section Summary 6.3 pages 296 - 301
Causes of Mutations

• The breaking and reforming of a double-stranded
  DNA molecule can result in deletions.

• Chemical mutagens include dioxins, asbestos,
  benzene, and formaldehyde, substances that are
  commonly found in buildings and in the
  environment.

• Chemical mutagens usually cause substitution
  mutations.

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11.3 Section Summary 6.3 pages 296 - 301
Repairing DNA

• Repair mechanisms that fix mutations in cells
  have evolved.

• 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.