Transcript Part d

PowerPoint® Lecture Slides
prepared by
Janice Meeking,
Mount Royal College
CHAPTER
3
Cells: The
Living Units:
Part D
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Cell Cycle
• Defines changes from formation of the cell
until it reproduces
• Includes:
• Interphase
• Cell division (mitotic phase)
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Interphase
• Period from cell formation to cell division
• Nuclear material called chromatin
• Four subphases:
• G1 (gap 1)—vigorous growth and metabolism
• G0—gap phase in cells that permanently
cease dividing
• S (synthetic)—DNA replication
• G2 (gap 2)—preparation for division
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G1 checkpoint
(restriction point)
S
Growth and DNA
synthesis
G1
Growth
M
G2
Growth and final
preparations for
division
G2 checkpoint
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Figure 3.31
Interphase
Centrosomes
(each has 2
centrioles)
Nucleolus
Interphase
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Plasma
membrane
Chromatin
Nuclear
envelope
Figure 3.33
DNA Replication
• DNA helices begin unwinding from the
nucleosomes
• Helicase untwists the double helix and
exposes complementary chains
• The Y-shaped site of replication is the
replication fork
• Each nucleotide strand serves as a template
for building a new complementary strand
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DNA Replication
• DNA polymerase only works in one direction
• Continuous leading strand is synthesized
• Discontinuous lagging strand is synthesized in
segments
• DNA ligase splices together short segments of
discontinuous strand
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DNA Replication
• End result: two DNA molecules formed from
the original
• This process is called semiconservative
replication
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Chromosome
Free nucleotides
DNA polymerase
Old strand acts as a
template for synthesis
of new strand
Leading strand
Old DNA
Helicase unwinds
the double helix and
exposes the bases
Replication
fork
Adenine
Thymine
Cytosine
Guanine
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Two new strands (leading and lagging)
synthesized in opposite directions
Lagging
strand
DNA polymerase Old (template) strand
Figure 3.32
DNA Replication
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Cell Division
• Mitotic (M) phase of the cell cycle
• Essential for body growth and tissue repair
• Does not occur in most mature cells of
nervous tissue, skeletal muscle, and cardiac
muscle
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Cell Division
•
Includes two distinct events:
1. Mitosis—four stages of nuclear division:
•
Prophase
•
Metaphase
•
Anaphase
•
Telophase
2. Cytokinesis—division of cytoplasm by
cleavage furrow
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G1 checkpoint
(restriction point)
S
Growth and DNA
synthesis
G1
Growth
M
G2
Growth and final
preparations for
division
G2 checkpoint
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Figure 3.31
Cell Division
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Prophase
• Chromosomes become visible, each with two
chromatids joined at a centromere
• Centrosomes separate and migrate toward
opposite poles
• Mitotic spindles and asters form
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Prophase
• Nuclear envelope fragments
• Kinetochore microtubules attach to
kinetochore of centromeres and draw them
toward the equator of the cell
• Polar microtubules assist in forcing the poles
apart
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Early Prophase
Early mitotic
spindle
Aster
Early Prophase
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Chromosome
consisting of two
sister chromatids
Centromere
Figure 3.33
Late Prophase
Polar microtubule
Spindle pole
Fragments
of nuclear
envelope
Kinetochore
Late Prophase
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Kinetochore
microtubule
Figure 3.33
Metaphase
• Centromeres of chromosomes are aligned at
the equator
• This plane midway between the poles is
called the metaphase plate
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Metaphase
Spindle
Metaphase
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Metaphase
plate
Figure 3.33
Anaphase
• Shortest phase
• Centromeres of chromosomes split
simultaneously—each chromatid now
becomes a chromosome
• Chromosomes (V shaped) are pulled toward
poles by motor proteins of kinetochores
• Polar microtubules continue forcing the poles
apart
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Anaphase
Anaphase
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Daughter
chromosomes
Figure 3.33
Telophase
• Begins when chromosome movement stops
• The two sets of chromosomes uncoil to form
chromatin
• New nuclear membrane forms around each
chromatin mass
• Nucleoli reappear
• Spindle disappears
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Cytokinesis
• Begins during late anaphase
• Ring of actin microfilaments contracts to form
a cleavage furrow
• Two daughter cells are pinched apart, each
containing a nucleus identical to the original
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Nuclear
envelope
forming
Nucleolus
forming
Contractile
ring at
cleavage
furrow
Telophase and Cytokinesis
Telophase
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Figure 3.33
Control of Cell Division
• “Go” signals:
• Critical volume of cell when area of membrane
is inadequate for exchange
• Chemicals (e.g., growth factors, hormones,
cyclins, and cyclin-dependent kinases (Cdks))
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Control of Cell Division
• “Stop” signals:
• Contact inhibition
• Growth-inhibiting factors produced by
repressor genes
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Protein Synthesis
• DNA is the master blueprint for protein
synthesis
• Gene: Segment of DNA with blueprint for one
polypeptide
• Triplets of nucleotide bases form genetic
library
• Each triplet specifies coding for an amino acid
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Nuclear
envelope
Transcription
RNA Processing
DNA
Pre-mRNA
mRNA
Translation
Nuclear
pores
Ribosome
Polypeptide
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Figure 3.34
Roles of the Three Main Types of RNA
• Messenger RNA (mRNA)
• Carries instructions for building a polypeptide,
from gene in DNA to ribosomes in cytoplasm
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Roles of the Three Main Types of RNA
• Ribosomal RNA (rRNA)
• A structural component of ribosomes that,
along with tRNA, helps translate message
from mRNA
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Roles of the Three Main Types of RNA
• Transfer RNAs (tRNAs)
• Bind to amino acids and pair with bases of
codons of mRNA at ribosome to begin process
of protein synthesis
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Transcription
• Transfers DNA gene base sequence to a
complementary base sequence of an mRNA
• Transcription factor
• Loosens histones from DNA in area to be
transcribed
• Binds to promoter, a DNA sequence specifying
start site of gene to be transcribed
• Mediates the binding of RNA polymerase to
promoter
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Transcription
• RNA polymerase
• Enzyme that oversees synthesis of mRNA
• Unwinds DNA template
• Adds complementary RNA nucleotides on DNA
template and joins them together
• Stops when it reaches termination signal
• mRNA pulls off the DNA template, is further
processed by enzymes, and enters cytosol
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RNA polymerase
Coding strand
DNA
Promoter
region
Template strand
Termination
signal
1 Initiation: With the help of transcription factors, RNA
polymerase binds to the promoter, pries apart the two DNA strands,
and initiates mRNA synthesis at the start point on the template strand.
mRNA
Template strand
Coding strand of DNA
2 Elongation: As the RNA polymerase moves along the template
Rewinding
of DNA
strand, elongating the mRNA transcript one base at a time, it unwinds
the DNA double helix before it and rewinds the double helix behind it.
mRNA transcript
RNA nucleotides
Direction of
transcription
mRNA
DNA-RNA hybrid region
Template
strand
RNA
polymerase
3 Termination: mRNA synthesis ends when the termination signal
is reached. RNA polymerase and the completed mRNA transcript are
released.
Unwinding
of DNA
The DNA-RNA hybrid: At any given moment, 16–18 base pairs of
DNA are unwound and the most recently made RNA is still bound to
DNA. This small region is called the DNA-RNA hybrid.
Completed mRNA transcript
RNA polymerase
Copyright © 2010 Pearson Education, Inc.
Figure 3.35
RNA polymerase
Coding strand
DNA
Promoter
region
Template strand
Termination
signal
1 Initiation: With the help of transcription factors, RNA
polymerase binds to the promoter, pries apart the two DNA strands,
and initiates mRNA synthesis at the start point on the template strand.
Copyright © 2010 Pearson Education, Inc.
Figure 3.35 step 1
mRNA
Template strand
2 Elongation: As the RNA polymerase moves along the template
strand, elongating the mRNA transcript one base at a time, it unwinds
the DNA double helix before it and rewinds the double helix behind it.
mRNA transcript
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Figure 3.35 step 2
3 Termination: mRNA synthesis ends when the termination signal
is reached. RNA polymerase and the completed mRNA transcript are
released.
Completed mRNA transcript
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RNA
polymerase
Figure 3.35 step 3
Coding strand of DNA
Rewinding
of DNA
Unwinding
of DNA
RNA nucleotides
Direction of
transcription
mRNA
DNA-RNA hybrid region
Template
strand
RNA
polymerase
The DNA-RNA hybrid: At any given moment, 16–18 base pairs
of DNA are unwound and the most recently made RNA is still
bound to DNA. This small region is called the DNA-RNA hybrid.
Copyright © 2010 Pearson Education, Inc.
Figure 3.35 step 4
RNA polymerase
Coding strand
DNA
Promoter
region
Template strand
Termination
signal
1 Initiation: With the help of transcription factors, RNA
polymerase binds to the promoter, pries apart the two DNA strands,
and initiates mRNA synthesis at the start point on the template strand.
mRNA
Template strand
Coding strand of DNA
2 Elongation: As the RNA polymerase moves along the template
Rewinding
of DNA
strand, elongating the mRNA transcript one base at a time, it unwinds
the DNA double helix before it and rewinds the double helix behind it.
mRNA transcript
RNA nucleotides
Direction of
transcription
mRNA
DNA-RNA hybrid region
Template
strand
RNA
polymerase
3 Termination: mRNA synthesis ends when the termination signal
is reached. RNA polymerase and the completed mRNA transcript are
released.
Unwinding
of DNA
The DNA-RNA hybrid: At any given moment, 16–18 base pairs of
DNA are unwound and the most recently made RNA is still bound to
DNA. This small region is called the DNA-RNA hybrid.
Completed mRNA transcript
RNA polymerase
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Figure 3.35
Translation
• Converts base sequence of nucleic acids into
the amino acid sequence of proteins
• Involves mRNAs, tRNAs, and rRNAs
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Genetic Code
• Each three-base sequence on DNA is
represented by a codon
• Codon—complementary three-base sequence
on mRNA
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SECOND BASE
C
A
U
UUU
U
UUC
UUA
UUG
Phe
Leu
CUU
C
CUC
CUA
A
Leu
UCC
UAC
UCA
Ser
UAA
UCG
UAG
CCU
CAU
CCC
CCA
Pro
CAC
CAA
CCG
CAG
AUU
ACU
AAU
ACC
AAC
AUC
Ile
ACA
Thr
AAA
Met or
AUG Start ACG
AAG
GUU
GCU
GAU
GUC
GCC
GAC
GUA
GUG
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UAU
CUG
AUA
G
UCU
Val
GCA
GCG
Ala
GAA
GAG
G
Tyr
UGU
UGC
U
Cys
C
Stop UGA Stop A
Stop UGG
Trp G
His
Gln
Asn
Lys
Asp
Glu
U
CGU
CGC
CGA
C
Arg
A
CGG
G
AGU
U
AGC
AGA
AGG
Ser
C
A
Arg
G
GGU
U
GGC
C
GGA
GGG
Gly
A
G
Figure 3.36
Translation
• mRNA attaches to a small ribosomal subunit that
moves along the mRNA to the start codon
• Large ribosomal unit attaches, forming a functional
ribosome
• Anticodon of a tRNA binds to its complementary
codon and adds its amino acid to the forming protein
chain
• New amino acids are added by other tRNAs as
ribosome moves along rRNA, until stop codon is
reached
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Nucleus
RNA polymerase
mRNA
Leu
Template
strand of
DNA
1 After mRNA synthesis in the
nucleus, mRNA leaves the nucleus
and attaches to a ribosome.
Energized by ATP, the correct amino
acid is attached to each species of
tRNA by aminoacyl-tRNA synthetase
enzyme.
Amino acid
Nuclear pore
tRNA
Nuclear
membrane
G A A
2 Translation begins as incoming
aminoacyl-tRNA recognizes the
complementary codon calling for
it at the A site on the ribosome. It
hydrogen-bonds to the codon via
its anticodon.
Released mRNA
Aminoacyl-tRNA
synthetase
Leu
3 As the ribosome moves along
the mRNA, and each codon is
read in sequence, a new amino
acid is added to the growing
protein chain and the tRNA in
the A site is translocated to the
P site.
Ile
tRNA “head”
bearing
anticodon
Pro
4 Once its amino acid is released
from the P site, tRNA is ratcheted
to the E site and then released to
reenter the cytoplasmic pool,
ready to be recharged with a new
amino acid. The polypeptide is
released when the stop codon is
read.
E
site
P
site
G G C
A
site
A U A C C G
C U U
Codon
15
Codon
17
Codon
16
Large
ribosomal
subunit
Small
ribosomal
subunit
Direction of
Portion of mRNA ribosome advance
already translated
Copyright © 2010 Pearson Education, Inc.
Figure 3.37
Nucleus
mRNA
RNA polymerase
Template
strand of
DNA
1
After mRNA synthesis in
the nucleus, mRNA leaves the
nucleus and attaches to a
ribosome.
Energized by ATP, the correct
amino acid is attached to each
species of tRNA by aminoacyltRNA synthetase enzyme.
Leu
Amino acid
Nuclear pore
tRNA
Nuclear
membrane
GAA
Released mRNA
Aminoacyl-tRNA
synthetase
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Figure 3.37 step 1
Leu
Ile
2 Translation begins as
incoming aminoacyl-tRNA
recognizes the
complementary codon
calling for it at the A site
on the ribosome. It
hydrogen-bonds to the
codon via its anticodon.
tRNA “head”
bearing
anticodon
Pro
E
site
P
site
G G C
A
site
Large
ribosomal
subunit
A U A C C G C U U
Codon Codon
15
16
Codon
17
Small
ribosomal
subunit
Direction of
Portion of
ribosome advance
mRNA already
translated
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Figure 3.37 step 2
Leu
3 As the ribosome moves
along the mRNA, and each
codon is read in sequence, a
new amino acid is added to
the growing protein chain and
the tRNA in the A site is
translocated to the P site.
Ile
2 Translation begins as
incoming aminoacyl-tRNA
recognizes the
complementary codon
calling for it at the A site
on the ribosome. It
hydrogen-bonds to the
codon via its anticodon.
tRNA “head”
bearing
anticodon
Pro
E
site
P
site
G G C
A
site
Large
ribosomal
subunit
A U A C C G C U U
Codon Codon
15
16
Codon
17
Small
ribosomal
subunit
Direction of
Portion of
ribosome advance
mRNA already
translated
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Figure 3.37 step 3
Leu
3 As the ribosome moves
along the mRNA, and each
codon is read in sequence, a
new amino acid is added to
the growing protein chain and
the tRNA in the A site is
translocated to the P site.
Ile
2 Translation begins as
incoming aminoacyl-tRNA
recognizes the
complementary codon
calling for it at the A site
on the ribosome. It
hydrogen-bonds to the
codon via its anticodon.
tRNA “head”
bearing
anticodon
Pro
4 Once its amino acid is
released from the P site, tRNA
is ratcheted to the E site and
then released to reenter the
cytoplasmic pool, ready to be
recharged with a new amino
acid. The polypeptide is
released when the stop
codon is read.
E
site
P
site
G G C
A
site
Large
ribosomal
subunit
A U A C C G C U U
Codon Codon
15
16
Codon
17
Small
ribosomal
subunit
Direction of
Portion of
ribosome advance
mRNA already
translated
Copyright © 2010 Pearson Education, Inc.
Figure 3.37 step 4
Nucleus
RNA polymerase
mRNA
Leu
Template
strand of
DNA
1 After mRNA synthesis in the
nucleus, mRNA leaves the nucleus
and attaches to a ribosome.
Energized by ATP, the correct amino
acid is attached to each species of
tRNA by aminoacyl-tRNA synthetase
enzyme.
Amino acid
Nuclear pore
tRNA
Nuclear
membrane
G A A
2 Translation begins as incoming
aminoacyl-tRNA recognizes the
complementary codon calling for
it at the A site on the ribosome. It
hydrogen-bonds to the codon via
its anticodon.
Released mRNA
Aminoacyl-tRNA
synthetase
Leu
3 As the ribosome moves along
the mRNA, and each codon is
read in sequence, a new amino
acid is added to the growing
protein chain and the tRNA in
the A site is translocated to the
P site.
Ile
tRNA “head”
bearing
anticodon
Pro
4 Once its amino acid is released
from the P site, tRNA is ratcheted
to the E site and then released to
reenter the cytoplasmic pool,
ready to be recharged with a new
amino acid. The polypeptide is
released when the stop codon is
read.
E
site
P
site
G G C
A
site
A U A C C G
C U U
Codon
15
Codon
17
Codon
16
Large
ribosomal
subunit
Small
ribosomal
subunit
Direction of
Portion of mRNA ribosome advance
already translated
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Figure 3.37
Role of Rough ER in Protein Synthesis
• mRNA–ribosome complex is directed to rough
ER by a signal-recognition particle (SRP)
• Forming protein enters the ER
• Sugar groups may be added to the protein,
and its shape may be altered
• Protein is enclosed in a vesicle for transport to
Golgi apparatus
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1 The mRNA-ribosome complex is
directed to the rough ER by the SRP.
There the SRP binds to a receptor site.
ER signal
sequence
2 Once attached to the ER, the SRP is released
and the growing polypeptide snakes through the
ER membrane pore into the cisterna.
3 The signal sequence is clipped off by an
enzyme. As protein synthesis continues, sugar
groups may be added to the protein.
Ribosome
mRNA
Signal
Signal
recognition
sequence
particle Receptor site
removed
(SRP)
Growing
polypeptide
4 In this example, the completed
protein is released from the ribosome
and folds into its 3-D conformation,
a process aided by molecular chaperones.
Sugar
group
5 The protein is enclosed within a
protein (coatomer)-coated transport
vesicle. The transport vesicles make
their way to the Golgi apparatus,
where further processing of the
proteins occurs (see Figure 3.19).
Released
protein
Rough ER cisterna
Cytoplasm
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Transport vesicle
pinching off
Coatomer-coated
transport vesicle
Figure 3.39
1 The mRNA-ribosome complex is
directed to the rough ER by the SRP.
There the SRP binds to a receptor site.
ER signal
sequence
Ribosome
mRNA
Signal
recognition
particle Receptor site
(SRP)
Rough ER cisterna
Cytoplasm
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Figure 3.39 step 1
1 The mRNA-ribosome complex is
directed to the rough ER by the SRP.
There the SRP binds to a receptor site.
ER signal
sequence
2 Once attached to the ER, the SRP is released
and the growing polypeptide snakes through the
ER membrane pore into the cisterna.
Ribosome
mRNA
Signal
recognition
particle Receptor site
(SRP)
Growing
polypeptide
Rough ER cisterna
Cytoplasm
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Figure 3.39 step 2
1 The mRNA-ribosome complex is
directed to the rough ER by the SRP.
There the SRP binds to a receptor site.
ER signal
sequence
Ribosome
2 Once attached to the ER, the SRP is released
and the growing polypeptide snakes through the
ER membrane pore into the cisterna.
3 The signal sequence is clipped off by an
enzyme. As protein synthesis continues, sugar
groups may be added to the protein.
mRNA
Signal
Signal
recognition
sequence
particle Receptor site
removed
(SRP)
Growing
polypeptide
Sugar
group
Rough ER cisterna
Cytoplasm
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Figure 3.39 step 3
1 The mRNA-ribosome complex is
directed to the rough ER by the SRP.
There the SRP binds to a receptor site.
ER signal
sequence
2 Once attached to the ER, the SRP is released
and the growing polypeptide snakes through the
ER membrane pore into the cisterna.
3 The signal sequence is clipped off by an
enzyme. As protein synthesis continues, sugar
groups may be added to the protein.
Ribosome
mRNA
Signal
Signal
recognition
sequence
particle Receptor site
removed
(SRP)
Growing
polypeptide
4 In this example, the completed
protein is released from the ribosome
and folds into its 3-D conformation,
a process aided by molecular chaperones.
Sugar
group
Released
protein
Rough ER cisterna
Cytoplasm
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Figure 3.39 step 4
1 The mRNA-ribosome complex is
directed to the rough ER by the SRP.
There the SRP binds to a receptor site.
ER signal
sequence
2 Once attached to the ER, the SRP is released
and the growing polypeptide snakes through the
ER membrane pore into the cisterna.
3 The signal sequence is clipped off by an
enzyme. As protein synthesis continues, sugar
groups may be added to the protein.
Ribosome
mRNA
Signal
Signal
recognition
sequence
particle Receptor site
removed
(SRP)
Growing
polypeptide
4 In this example, the completed
protein is released from the ribosome
and folds into its 3-D conformation,
a process aided by molecular chaperones.
Sugar
group
5 The protein is enclosed within a
protein (coatomer)-coated transport
vesicle. The transport vesicles make
their way to the Golgi apparatus,
where further processing of the
proteins occurs (see Figure 3.19).
Released
protein
Rough ER cisterna
Cytoplasm
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Transport vesicle
pinching off
Coatomer-coated
transport vesicle
Figure 3.39 step 5
Other Roles of DNA
• Intron (“junk”) regions of DNA code for other types of
RNA:
• Antisense RNA
• Prevents protein-coding RNA from being translated
• MicroRNA
• Small RNAs that interfere with mRNAs made by
certain exons
• Riboswitches
• Folded RNAs that act as switches regulating protein
synthesis in response to environmental conditions
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Cytosolic Protein Degradation
• Nonfunctional organelle proteins are
degraded by lysosomes
• Ubiquitin tags damaged or unneeded soluble
proteins in cytosol; they are digested by
enzymes of proteasomes
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Extracellular Materials
• Body fluids (interstitial fluid, blood plasma,
and cerebrospinal fluid)
• Cellular secretions (intestinal and gastric
fluids, saliva, mucus, and serous fluids)
• Extracellular matrix (abundant jellylike mesh
containing proteins and polysaccharides in
contact with cells)
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Developmental Aspects of Cells
• All cells of the body contain the same DNA but are
not identical
• Chemical signals in the embryo channel cells into
specific developmental pathways by turning some
genes off
• Development of specific and distinctive features in
cells is called cell differentiation
• Elimination of excess, injured, or aged cells occurs
through programmed rapid cell death (apoptosis)
followed by phagocytosis
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Theories of Cell Aging
• Wear and tear theory: Little chemical insults
and free radicals have cumulative effects
• Immune system disorders: Autoimmune
responses and progressive weakening of the
immune response
• Genetic theory: Cessation of mitosis and cell
aging are programmed into genes. Telomeres
(strings of nucleotides on the ends of
chromosomes) may determine the number of
times a cell can divide.
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