Transcript chapter8_Sections 1-3.ppt

Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 8
DNA Structure and Function
(Sections 8.1 - 8.3)
Albia Dugger • Miami Dade College
8.1 A Hero Dog’s Golden Clones
• Making clones of adult animals is a common practice that
continues to raise serious ethical questions
• Cloning techniques are not perfect; many attempts are
required to produce a clone, and clones often have health
problems
• clone
• Genetically identical copy of an organism
A Hero Dog
• Canadian police officer
James Symington’s
search-and-rescue dog
Trakr led rescuers to the
fifth and final survivor of
the World Trade Center
attacks
Trakr’s Golden Clones
• Trakr died of a degenerative disease probably linked to toxic
smoke at Ground Zero – but his DNA lives on in his clones
• Trakr won the Golden Clone Giveaway, a contest to find the
world’s most clone-worthy dog
• Trakr’s DNA was shipped to Korea, inserted into dog eggs,
and implanted into surrogate mother dogs
Clone Puppies
• Trakr’s clones were delivered to Symington in July 2009
8.2 Eukaryotic Chromosomes
• All organisms pass DNA to offspring when they reproduce
•
In cells, each DNA molecule is organized as a chromosome
• chromosome
• Structure consisting of DNA and associated proteins
• Carries part or all of a cell’s genetic information
• Eukaryotic cells have a number of chromosomes
Chromosome Duplication
• During most of a cell’s life, each of its chromosomes consists
of one DNA molecule
• As it prepares to divide, the cell duplicates its chromosomes,
so both offspring get a full set
• After chromosomes are duplicated, each consists of two DNA
molecules (sister chromatids) attached to each other at a
centromere
Key Terms
• sister chromatid
• One of two attached members of a duplicated eukaryotic
chromosome
• centromere
• Constricted region in a eukaryotic chromosome where
sister chromatids are attached
Chromosome Duplication
Chromosome Duplication
centromere
one chromatid
its sister chromatid
a chromosome
(unduplicated)
a chromosome
(duplicated)
p. 124
Sister Chromatids
• A duplicated chromosome consists of two long, tangled
filaments (sister chromatids) bunched into an X shape
Chromosome Structure
1. DNA in a nucleus is divided into chromosomes
2. At its most condensed, a duplicated chromosome is packed
tightly into an X shape
3. A chromosome unravels as a single fiber – a hollow cylinder
formed by coiled coils
4. The coiled coils consist of a long molecule of DNA and
associated proteins
5. The DNA molecule wraps around a core of histone proteins,
forming “beads” called nucleosomes
6. The DNA molecule has two strands twisted in a double helix
Key Terms
• histone
• Type of protein that structurally organizes eukaryotic
chromosomes
• nucleosome
• A length of DNA wound around a spool of histone proteins
1 The DNA inside the nucleus of a
eukaryotic cell is typically divided
up into a number of chromosomes.
Inset: a duplicated human
chromosome.
Chromosome
Structure
2 At its most condensed, a
duplicated chromosome
is packed tightly into an X
shape.
3 A chromosome unravels
as a single fiber, a hollow
cylinder formed by coiled
coils.
4 The coiled coils consist of a
long molecule of DNA (blue) and
the proteins that are associated
with it (purple).
5 At regular intervals, the DNA
molecule is wrapped twice around
a core of histone proteins. In this
“beads-on-a-string” structure, the
“string” is the DNA, and each
“bead” is called a nucleosome.
6 The DNA molecule itself has two
strands that are twisted into a
double helix.
Fig 8.2a, p. 124
ANIMATION: Chromosome structural
organization
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Chromosome Number
• Eukaryotic DNA is divided among a number of
chromosomes that differ in length and shape
• The sum of all chromosomes in a cell of a given type is the
chromosome number
• Diploid cells have two of each type of chromosome
• Each species has a characteristic chromosome number
Key Terms
• chromosome number
• Sum of all chromosomes in a cell of a given type
• diploid
• Having two of each type of chromosome characteristic of
the species (2n)
Human Chromosome Number
• Human body cells have 46 chromosomes (chromosome
number 46)
• Human body cells have two of each type of chromosome (23
pairs) so the chromosome number is diploid (2n)
• Each pair of chromosomes has two versions, one maternal
and one paternal
Types of Chromosomes
• Members of a pair of sex chromosomes differ among males
and females – the differences determine an individual’s sex
• All others chromosomes are autosomes, which are the same
in both females and males
• Autosomes of a pair have the same length, shape, and
centromere location, and carry the same genes
Key Terms
• sex chromosome
• Member of a pair of chromosomes that differs between
males (XY) and females (XX)
• autosome
• Any chromosome other than a sex chromosome
• The two members of each pair have the same length and
shape, and hold information about the same traits
Karyotype
• A karyotype can reveal abnormalities in an individual’s
complement of chromosomes
• A micrograph of a single cell is digitally rearranged so images
of chromosomes are lined up by centromere location, and
arranged according to size, shape, and length
• karyotype
• Image of an individual’s complement of chromosomes
arranged by size, length, shape, and centromere location
A Human Karyotype
• 22 pairs of autosomes and 2 X chromosomes
ANIMATION: Karyotype preparation
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Sex Determination in Humans
• Body cells of human females contain two X chromosomes
(XX); those of males contain one X and one Y (XY)
• New individuals randomly inherit one sex chromosome from
the mother and one from the father
• All female eggs have one X chromosome
• Male sperm have either an X or a Y (50-50 chance)
• If an X-bearing sperm fertilizes an X-bearing egg, the
resulting individual will be female – if the sperm carries a Y
chromosome, the individual will develop into a male
Sex Determination in Humans
diploid
reproductive
cell in female
diploid
reproductive
cell in male
eggs
Sex
Determination
in Humans
sperm
union of sperm and
egg at fertilization
Fig 8.4, p. 125
diploid
reproductive
cell in female
diploid
reproductive
cell in male
eggs
Sex
Determination
in Humans
sperm
XX
XY
XX
XY
union of sperm and
egg at fertilization
Stepped Art
Fig 8.4, p. 125
ANIMATION: Human sex determination
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Key Concepts
• Chromosomes
• DNA of a eukaryotic cell is divided among a characteristic
number of chromosomes that differ in length and shape
• Sex chromosomes determine an individual’s gender
• Proteins associated with eukaryotic DNA help organize
chromosomes so they can pack into a nucleus
8.3 Discovery of DNA’s Function
• Almost one hundred years of experiments with bacteria and
bacteriophage offer solid evidence that deoxyribonucleic acid
(DNA), not protein, is the hereditary material of life
Early and Puzzling Clues
• Late 1800s:
• Johannes Miescher found that nuclei contain an acidic
substance composed mostly of nitrogen and phosphorus
• Later, that substance would be called deoxyribonucleic
acid (DNA)
• Early 1900s:
• Frederick Griffith used two strains of Streptococcus
pneumoniae in a series of experiments that revealed a
clue about inheritance
Griffith’s Experiments
• Griffith isolated two strains (types) of Streptococcus
pneumoniae, a bacteria that causes pneumonia: harmless,
rough (R) and killer, smooth (S)
• The hereditary material of harmful Streptococcus pneumoniae
cells was transferred from dead S cells into live R cells –
transforming harmless cells (R) into killers (S)
• The transformation was permanent and heritable
Griffith’s Experiments
1. Mice injected with live
cells of harmless strain R
do not die
• Live R cells in blood
2. Mice injected with live
cells of strain S die
• Live S cells in blood
Griffith’s Experiments (cont.)
3. Mice injected with heatkilled S cells do not die
• No live S cells in blood
4. Mice injected with live R
cells plus heat-killed S
cells die
• Live S cells in blood
Griffith’s Experiments
Mice injected with
live cells of harmless
strain R do not die.
Live R cells in their
blood.
1
Mice injected with
live cells of killer
strain S die. Live S
cells in their blood.
2
Mice injected
with heat-killed S
cells do not die.
No live S cells in
their blood.
3
Mice injected
with live R cells
plus heat-killed S
cells die. Live S
cells in their
blood.
4
Fig 8.5, p. 126
ANIMATION: Griffith's experiment
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More Clues
• 1940s: Oswald Avery and Maclyn McCarty tried to identify
Griffiths “transforming principle”
• Separated lipid, protein, and nucleic acid components of S
cells
• S cell extract still transformed R cells after treatment with
lipid- and protein-destroying enzymes, so transforming
principle must be nucleic acid (RNA or DNA)
• S cell extract still transformed R cells after treatment with
RNA-degrading enzymes, but not after treatment with
DNA-degrading enzymes, so DNA had to be the
transforming principle
Confirmation of DNA’s Function
• Alfred Hershey and Martha Chase tested whether genetic
material injected by bacteriophages into bacteria is DNA,
protein, or both
• Based on the fact that proteins contain more sulfur than
phosphorus, and DNA contains more phosphorus than sulfur
• bacteriophage
• Virus that infects bacteria
Bacteriophages
• Top, model of a
bacteriophage
• Bottom, micrograph of
three viruses injecting
DNA into an E. coli cell
Bacteriophages
DNA
inside
protein
coat
tail
fiber
hollow
sheath
Fig 8.6a.1, p. 127
Bacteriophages
Fig 8.6a.2, p. 127
Hershey–Chase Experiment 1.
• Bacteria were infected with virus particles that had proteins
labeled with a radioisotope of sulfur (35S)
• Viruses were dislodged from the bacteria by whirling the
mixture in a kitchen blender
• Most radioactive sulfur was detected in viruses, not in
bacterial cells
• Viruses had not injected protein into the bacteria
Hershey–Chase Experiment 1
Hershey–Chase Experiment 1
Virus particle
coat proteins
labeled with 35S
35S
remains
outside cells
DNA being
injected into
bacterium
B In one experiment, bacteria were infected with virus particles that had been labeled
with a radioisotope of sulfur (35S). The sulfur had labeled only viral proteins. The viruses
were dislodged from the bacteria by whirling the mixture in a kitchen blender. Most of the
radioactive sulfur was detected in the viruses, not in the bacterial cells. The viruses had
not injected protein into the bacteria.
Fig 8.6b, p. 127
Hershey–Chase Experiment 2
• Bacteria were infected with virus particles that had DNA
labeled with a radioisotope of phosphorus (32P)
• When viruses were dislodged from the bacteria, radioactive
phosphorus was detected mainly inside the bacterial cells
• Viruses had injected DNA into the cells—evidence that DNA is
the genetic material of this virus
Hershey–Chase Experiment 2
Hershey–Chase Experiment 2
Virus DNA
labeled with 32P
32P
remains
inside cells
Labeled DNA
being injected
into bacterium
C In another experiment, bacteria were infected with virus particles that had been labeled
with a radioisotope of phosphorus (32P). The phosphorus had labeled only viral DNA. When
the viruses were dislodged from the bacteria, the radioactive phosphorus was detected
mainly inside the bacterial cells. The viruses had injected DNA into the cells—evidence that
DNA is the genetic material of this virus.
Fig 8.6c, p. 127
Hershey–Chase Experiment 2
Virus particle
coat proteins
labeled with 35S
35S
remains
outside cells
DNA being
injected into
bacterium
Virus DNA
labeled with 32P
32P
remains
inside cells
Labeled DNA
being injected
into bacterium
Stepped Art
Fig 8.6, p. 127
ANIMATION: Hershey-Chase experiments
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Key Concepts
• Discovery of DNA’s Function
• The work of many scientists over more than a century led
to the discovery that DNA is the molecule that stores
hereditary information