Chapters 12 13 16 17 Limits to Cell Growth The larger a cell becomes the more demands a cell places on its DNA If extra copies of DNA are not made an information crisis would occur The cell also has more trouble moving nutrients and wastes across the cell membrane ID: 921133
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Slide1
Cell Unit III: Cell Division, Cell Cycle, Transcription and Translation
Chapters 12, 13, 16, 17
Slide2Limits to Cell Growth
The larger a cell becomes, the more demands a cell places on its DNA
If extra copies of DNA are not made, an “information crisis” would occur
The cell also has more trouble moving nutrients and wastes across the cell membrane
Food, oxygen, water, and wastes move through the cell membrane
The rate at which the exchange takes place depends on the surface area of the cell
The rate at which food and oxygen are used up and wastes produced depends on the cell’s volume
Slide3Ratio of Surface Area to Volume
Volume increases much more rapidly than surface area causing the ratio of surface area to volume to decrease
This decrease creates serious problems for the cell such as:
Inability to remove wastes from the cell
Lack of sufficient oxygen and food entering through the cell membrane
Slide4Division of the Cell
The process by which a cell divides into two new daughter cells is called cell division
Before cell division occurs, the cell replicates, or copies, all of its DNA
Each daughter cell gets one complete set of genetic information
Each daughter cell also has an increased ratio of surface area to volume
Slide5Slide6Cell Division
Each cell has only one set of genetic information
must be copied before cell division begins
The first stage, division of the cell nucleus, is called mitosis
The second stage, division of the cytoplasm, is called cytokinesis
Reproduction by mitosis is classified as asexual
Mitosis is the source of new cells when a multicellular organism grows and develops
Slide7Slide8Chromosomes
Chromosomes are made of DNA (genetic information) and proteins (histones)
The cells of every organism have a specific number of chromosomes
Fruit flies = 8, human = 46, carrots = 18
Chromosomes are not visible in most cells except during cell division
Each chromosome consists of two identical sister chromatids which separate during cell division
Each pair of chromatids is attached in an area called the centromere
Slide9Slide10The Cell Cycle
Interphase is the period in between periods of cell division
The cell cycle is the series of events that cells go through as they grow and divide
During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells, each of which then begins the cycle again
The cell cycle consists of four phases
M, S, G
1
, and G
2
Slide11The Cell Cycle
Slide12The Cell Cycle
Slide13Events of the Cell Cycle
During the normal cell cycle, interphase can be quite long, whereas the process of cell division takes place quickly
The G
1
phase is a period in which cells do most of their growing
In the S phase, chromosomes are replicated and the synthesis of DNA molecules takes place
During the G
2
phase, many of the organelles and molecules required for cell division are produced
Slide14Slide15Mitosis
Prophase:
Chromosomes become visible, centrioles begin to organize the spindle and move to opposite ends of the cell, fibers attach to centromeres, nucleolus and nuclear envelope disappear
Metaphase:
Chromosomes line up across the center of the cell
Anaphase:
Centromeres split and individual
chromatids
are separated into two groups near the poles
Telophase:
Chromosomes disperse, nuclear envelope and nucleolus re-form, spindle breaks apart
Slide16Mitosis
Slide17Cytokinesis
Cytokinesis
is the division of the cytoplasm itself and usually occurs at the same time as
telophase
In most animal cells, the cytoplasm is drawn inward until the cytoplasm is pinched into two nearly equal parts. This is called a cleavage furrow.
In plants, a structure known as the cell plate forms midway between the divided nuclei
Slide18Slide19Cytokinesis in Animal Cells
Slide20Controls on Cell Division
When placed on a petri dish with a thin layer of nutrient solution, cells will grow until they form a thin layer on the bottom of the dish
When cells come into contact with other cells, they respond by not growing
If cells are removed from the center of the dish, the cells bordering the open space will divide until they have filled the space
Controls on cell growth and division can be turned off and on
Slide21Cell Cycle Regulators
Several scientists discovered that cells in mitosis contained a protein that when injected into a
nondividing
cell, would cause a mitotic spindle to form
They called this protein
cyclin
because it seemed to regulate the cell cycle
Cyclins
regulate the timing of the cell cycle in eukaryotic cells
Proteins that respond to events inside the cell are called internal regulators
External regulators respond to events outside of the cell
Slide22Cell Cycle Regulators
Slide23Uncontrolled Cell Growth
Cancer is a disorder in which some of the body’s own cells lose the ability to control growth
Cancer cells do not respond to the signals that regulate the growth of most cells
They divide uncontrollable and form masses of cells called tumors that can damage the surrounding tissues
Causes include smoking, radiation, and viral infections
Damaged or defective p53 genes cause the cells to lose the information needed to respond to signals that would normally control their growth
Slide24p53
is a protein that functions to block the cell cycle if the DNA is damaged. If the damage is
severe,
this protein can cause apoptosis (cell death).
p53 levels are increased in damaged cells. This allows time to repair DNA by blocking the cell cycle.
A p53 mutation is the most frequent mutation leading to cancer.
p27
is a protein that binds to
cyclin
and
cdk
blocking entry into S phase. Recent research (
Nature Medicine
3, 152 (1997)) suggests that breast cancer prognosis is determined by p27 levels. Reduced levels of p27 predict a poor outcome for breast cancer patients.
Uncontrolled Cell Growth
Slide27CHAPTER 13: MEIOSIS AND SEXUAL CYCLES
Meiosis
- cell division that reduces the diploid # to the haploid # in the formation of sex cells (gametes).
Example (
Humans)
- 46 chromosomes is reduced to 23.
MOST IMPORTANT
- the cells produced at the end of meiosis contain one chromosome of each
homologous
(matching) pair.
Slide28GENE
-
HEREDITARY INFORMATION, IN A SECTION OF A DNA
MOLECULE ON A CHROMOSOME.
LOCUS (LOCI)
- A GENE’S SPECIFIC LOCATION ON A CHROMOSOME.
TERMS:
CLONE
- A GROUP OF GENETICALLY IDENTICAL INDIVIDUALS
(
WHAT MITOSIS PRODUCES)
ASEXUAL REPRODUCTION
- REPRODUCTION
W/O
SEX (NO MALE/FEMALE;
1
PARENT; OFFSPRING
IS A CLONE OF PARENT.
HOMOLOGOUS CHROMOSOMES
- A MATCHING PAIR ALWAYS ONE FROM EACH PARENT.(one paternal/ one maternal.)
Slide29AUTOSOMES
- CHROMOSOMES NOT DIRECTLY INVOLVED IN DETERMINING SEX. (IN
HUMANS: 22
HOMOLOGOUS PAIR).
SEX CHROMOSOMES
- THE CHROMOSOMES DIRECTLY INVOLVED IN DETERMINING SEX (IN HUMANS THE LAST HOMOLOGOUS PAIR).
(a) CALLED (X) & (Y) CHROMOSOMES.
(b) XX = FEMALE & XY = MALE.
FERTILIZATION
(or SYNGAMY)
- UNION OF GAMETES.
KARYOTYPE:
DISPLAY
OF AN INDIVIDUAL’S CHROMOSOMES. CHROMOSOMES ARE COLLECTED DURING
METAPHASE
.
THIS IS DONE BY NUMBER, SIZE & TYPE CHROMOSOME.
(c) In other organisms:
(1) Insects (Grasshoppers, Roaches): X-O sex chromosomes. O represents no sex chromosome = Male
(2) Birds, Butterflies and some fish: Z-W sex chromosomes. Female gamete determines sex. Males are ZZ, Females are ZW
(3) Parthenogenesis – wasps, bees and ants. If the egg is fertilized it becomes a female and is diploid. If the egg is unfertilized it is male and haploid.
Slide30THE HUMAN LIFE CYCLE:
(
characteristic of most animals)
Gametes are the only haploid cells.
The diploid zygote divides by mitosis producing a diploid organism.
Slide31MEIOSIS STEPS
:
(
FIG. 13.5.)
(a) Each chromosome replicates. (This shows 1 homologous pair). Remember - sister chromatids & centromere.
(b)
Meiosis I
segregates the homologous pair into 2 different cells (each new daughter cell is in
HAPLOID
).
(c )
Meiosis II
separates sister chromatids into chromosomes. No chromosome duplication)
Slide32MEIOSIS TERMS:
Synapsis
- ( in
prophase I
) - the duplicated chromosomes pair with their Homologues). This is a
PROCESS.
Homologous chromosomes made of two sister chromatids come together as pairs.
Homologue
- one of a homologous pair.
Tetrad
- the four closely associated chromatids of a homologous pair together. This happens during synapsis.
Crossing over
- (
a process
) reciprocal exchange of genetic material between
nonsister
chromatids
.
Slide33COMPARING
MITOSIS & MEIOSIS.
MEIOSIS
- Prophase I with -(a) Tetrad & synapsis making a synaptonemal complex (b) Crossing over with the chiasma.
MITOSIS
- No tetrads,
synapsis
, or
crossing over.
DAUGHTER CELL DIFFERENCE -
Mitosis has produced 2 identical cells. Meiosis produced daughter cells with one of each homologous pair.
Slide34SUMMARY
:
differences
between Mitosis & Meiosis.
Slide35FIG. 13.8
-
This shows the most
important concept of meiosis (how it produces
genetic variation
in organisms).
INDEPENDENT ASSORTMENT:
At the end of meiosis chromosome pairs distribute themselves independently of one another. This causes 4 different combinations of chromosomes with 2 homologous pair.
Slide361st MEIOTIC DIVISION
RESULTS IN INDEPENDENT ASSORTMENT OF MATERNAL & PATERNAL CHROMOSOMES IN DAUGHTER CELLS.
FORMULA:
The number of combinations possible when chromosomes assort independently into gametes during meiosis is 2
n
, where (n) is the haploid # in the organism.
EXAMPLE
-
Human haploid (n) is 23. 2
23
is over 8 million. A male can produce 8 million genetically different combinations of sperm & a female 8 million combinations of eggs.
RANDOM FERTILIZATION
then would produce 8 million x 8 million(over 64 Trillion) possibly different genetic combinations in the offspring.
Slide37Crossing
Over -
produces individual chromosomes that combine genes inherited from our two parents.
Independent Assortment, Random Fertilization, & Crossing Over
- result ways that genetic variation can be produced.
Slide38SUMMARY:
Prophase I & Anaphase I
produce the most variation in the 4 new daughter cells.
If clones were genetically different, this would be due to mutation (change in the code of DNA).
Remember these !!!!
Which might be a daughter cell of meiosis I ?
Which might be a daughter cell of meiosis II?
Slide39CHAPTER
16 - THE
MOLECULAR BASIS OF INHERITANCE
DNA
- most celebrated molecule of all time. It is made of nucleic acids that have the unique ability to direct their own replication.
PROBLEM
: Since a chromosome is made of protein & DNA which one is carrying the genetic material
?
There
can be an infinite # of proteins so it would be a prime candidate to carry genetic material.
Slide40JAMES WATSON
– CO-FOUNDER OF THE STRUCTURE OF DNA
Watson & Crick working on the DNA structure model. (April 1953)
Slide41Transformation
of Bacteria - Frederick Griffin.(1928)
The
captions under the picture is all that is needed to explain this experiment.
TRANSFORMATION
- the change in genotype & phenotype due to the assimilation of external DNA by a cell.
Slide42EVIDENCE THAT VIRAL DNA CAN PROGRAM CELLS (FIG. 16.2)
Virus is made of a protein coat & DNA core. Virus injects DNA into a
Bacteriophage
. DNA coat has radioactive protein coat (S
35)
while DNA is radiated with (P
32
).
HERSHEY-CHASE EXPERIMENT
That
the bacteria are called T2 Phages.
Slide43ADDITIONAL EVIDENCE THAT DNA IS THE GENETIC MATERIAL OF CELLS
Erwin Chargaff
- Said that the bases of DNA (A, T, C, G) vary from one species to another.
He
also found a regular ratio of bases. (A approximately = T; and G approx. = C). This was known as
Chargaff’s
Rules
.
NOTE:
All these discoveries were before Watson & Crick discovered the double helix structure of DNA.
Slide44Structure
of a DNA strand
DNA is composed of nucleotides ( 5 carbon sugar, phosphate & a nitrogenous base (A,T,C,G). Phosphate of one nucleotide is attached to the sugar of the next nucleotide.
Slide45Fig. 16.5 (a) The Double Helix Structure of DNA.
Adenine
(A) is always paired with Thymine (T) & Guanine (G) is always paired with Cytosine (C).
The
nitrogenous bases are held together with Hydrogen bonds (weak).
We
even know the distances between steps of the DNA rungs
. What’s a nm?
Slide46Notice
the strands are oriented in opposite directions.
This entire structure was worked out by Watson & Crick in 1953 with help from Rosalind Franklin’s x- ray diffraction photo of
DNA
Slide47Base
Pairing in DNA
.
A
& G are double ring compounds called
Purines
.
T
& C are single ring compounds called
Pyrimidines
.
Each
rung of DNA is made of a
Purine
attached to a
Pyrimidine
. Held together by H bonds.
Slide48The
SEMICONSERVATIVE
MODEL
- DNA replication model
Slide49Meselson
& Stahl tested the three hypothesis's on DNA
replication
Slide50B
eginnings
of how DNA Replicates.
Elongation of DNA at a replication fork is catalyzed by a enzyme called
DNA polymerase.
Rate of elongation in humans is approx.50/sec.
Slide51Adding a Nucleotide:
A
similar molecule to ATP (NTP) is used to link the new nucleotide to the proper position.
The enzyme that catalyzes the reaction is
DNA POLYMERASE.
THE
TWO STRAND OF DNA ARE
ANTIPARALLEL
Know:
Where
the 5’ & 3’ end are.
PROBLEM:
DNA polymerase can ONLY add nucleotides to the free 3’ end of a growing DNA strand.
So
..A new DNA strand can only elongate in the 5’ to 3’ direction.
Slide53SYNTHESIS
OF LEADING & LAGGING STRANDS DURING DNA REPLICATION.
DNA
polymerase is adding new DNA fragments in a 5’ to 3’ direction continuously along a replication fork, adding to the 3’ end.
Lagging
strand is synthesized in segments called Okazaki fragments. DNA
ligase
joins the fragments into a single DNA strand.
Okazaki fragments are about 100 -200 nucleotides long in eukaryotes.
Slide54PRIMING
DNA SYNTHESIS
DNA polymerase cannot initiate a polynucleotide strand; it can only add to the 3’ end of an already-started strand.
The
primer is a short segment of RNA synthesized by the enzyme
primase
.
Each primer is eventually replaced by DNA.
Slide55Slide56FIG. 16.15 - THE MAIN PROTEINS OF REPLICATION & THEIR FUNCTIONS.
DNA must also be able to form complementary base pairs with both DNA & RNA nucleotides. The sequence of nucleotides will be decoded into a sequence to make amino acids into proteins
.
Replication -> Transcription -> Translation
Slide57Enzymes
must proofread
DNA during its Replication and repair damage in existing DNA.
Mismatch Repair
fixes mistakes made in DNA. DNA polymerase itself carries out the mismatch repair.
Telomeres
- special sequences of DNA nucleotides found at the end of the DNA molecule. They do not contain genes. They protect the organism’s genes from being eroded through successive rounds of DNA replication
.
Secret to
aging?
http://www.youtube.com/watch?v=J9QApCHsrJk&feature=related
Slide58Image of Telomere
squeneces
(yellow) on chromosomes
Slide59Chapter 17 – From Gene to Protein
Transcription
- the synthesis of mRNA (messenger RNA) under the direction of DNA. This is a code to make a polypeptide (protein). This is also the synthesis of any RNA from DNA.
Translation
- the actual synthesis of a polypeptide (which occurs at the ribosomes.)
The difference
in Eukaryotic & Prokaryotic cells.
Gene to RNA to Protein.
Slide60Basics of the Genetic Code:
1. There is a total of 20 amino acids possible in any protein.
2. 3 Nucleotides on mRNA code for an amino acid. This is called the
triplet
code.
3. Only one strand of DNA is transcribed into mRNA. This strand is called the TEMPLATE strand. The other strand is called the complementary strand.
4. All Translation & Transcription occur in a 3’ to 5’ direction.
5. The mRNA is in triplet bases called CODONS.
Slide61mRNA
is only a single helix & that
Uracil
(U) is a substitute for Thymine (T).
The
number of nucleotides making up a genetic message must be 3 times the number of amino acids making up the protein.
EXAMPLE
- 4 amino acids
= 12
nucleotides
.
Amino Acids are connected by polypeptide bonds.
Slide62Learn to read this!!!
AUG
codon
is a start
codon
& the amino acid
Methionine
(Met).
Start
Codon
begins the sentence &
UAA,UAG & UGA = no amino acid but stops the amino acid chain (read in a 5’ to 3’
direction)= STOP CODON, like the period at the end of a sentence
Slide63Fig. 17.6 The Stages of Transcription
1. RNA binds to the promoter region of DNA (several dozen nucleotides “upstream” from the transcription startpoint).
2. RNA moves “downstream” from promoter, unwinding DNA & elongating RNA at the 3” end (5’ to 3’ direction).
Slide643. RNA polymerase transcribes a terminator (this sequence of nucleotides along DNA signals the end of transcription unit.)
4. Eventually RNA is released & the polymerase moves from DNA.
5.
Prokaryotes -
RNA transcript immediately used to make protein.
6.
Eukaryotes
- mRNA will undergo additional processing.
Progresses at about 60 nucleotides/sec in Eukaryotes.
Slide65RNA
Processing 1st step:
Enzymes modify 2 ends of a eukaryote pre-mRNA molecule.
Cap made of modified guanosine triphosphate added to the 5’ end of RNA.
A Poly(A) tail consiting of 200 adenine nucleotides attached to 3’ end
.
( may helps export mRNA from the nucleus.)
***Role of Cap and Tail - protect
RNA from
degradation****
The leader,
trailer & termination signal.
Leader
& trailer are not translated.
Slide66RNA
processing (splicing).
Pre-mRNA -
Exons
(Expressed sequence) are keep & the
Introns
(Intervening sequence) are removed (both by enzymes).
Exons
are then spliced together. We now have the processed RNA ready to leave the nucleus & go to the ribosome for translation
.
Slide67Translation - Basic Concept:
1)
tRNA
picks up amino acids & transport them to the
ribosome
2) Each
tRNA
has an
anticodon
(3 letters) that pick up one of the twenty amino acids.
3) When
the
tRNA’s
deliver their amino acid, they add them to a growing polypeptide chain.
tRNA’s
are now available to pick up another amino acid to repeat the process.
4) New Polypeptide
chain added in the 5’ to 3’ direction.
Slide68The
Anatomy of a
Ribosome:
Ribosomes
are made of 2 subunits each made of many molecules or
rRNA
(ribosomal
RNA) and proteins.
The
sites on the
ribosome:
(1)
P site
- holds the
tRNA
attached to the growing
polypeptide
(2)
A site
- holds the
tRNA
carrying the amino acid to be added to the polypeptide
chain
(3
) Discharged
tRNA
leaves via the
E site.
Peptide bonding between amino acids maintains the shape of
tRNA
.
Slide69Fig. 17.15 Initiation of Translation
1. Small ribosomal subunit binds to molecule of mRNA.
2. Initiator tRNA with anticodon UAC base-pairs with the start codon, AUG carrying the amino acid Met.
3. A large ribosomal unit arrives & completes the initiation complex.
4. Initiator tRNA is in the P site. A site is available to tRNA carrying the next amino acid.
5.
Proteins
called initiation factors bring translation components together. GTP provides the energy for all this.
Slide70GTP
& proteins called elongation factors needed to drive this process.
Slide71Termination
of Translation
1. When ribosome reaches a termination codon on mRNA, the (A) site of ribosome accepts a protein called a release factor instead of tRNA.
2. Release factor hydrolyzes the bond between tRNA in the P site & the last amino acid of the chain. This frees the polypeptide from the ribosome.
3.
The
2 ribosomal subunits dissociate
Slide72Fig. 17.18 Polyribosomes
A. An mRNA molecule is generally translated together with several ribosomes in clusters called
polyribosomes.
B. This enables a single mRNA to make many copies of a polypeptide simultaneously.
Slide73Proteins
can be chemically modified by attachment of sugars, lipids, phosphate groups etc.
Example:
Enzymes may remove leading amino acids from a chain. Sometimes several proteins will join together to allow them to function or one protein may split into several proteins.
Proteins
formed here are only the primary structure & must develop a secondary, tertiary, or even Quaternary structure.
Slide74Transcription
& Translation in
Bacteria:
Bacteria
(
Prokaroytes
) have no nucleus, so mRNA does not need to move through the membrane to the ribosome.
Streamlined
operations here - Transcription & Translation can be occurring at the same time.
3. There
is not RNA processing in bacteria. (All
exons
).
Slide75MUTATIONS:
Changes in the genetic code of DNA.
Point Mutations:
Chemical changes in just one or a few base pairs in a single gene.
If a point mutation occurs in a
gamete
or cells giving rise to
them,
it could be transmitted to offspring & future generations.
TYPES OF MUTATIONS:
1.
Base-pair substitution
- replacement of one nucleotide & its partner in the complementary DNA strand with another pair of nucleotides.
Some substitutions are
silent mutations
since genetic code is redundant, there may be no change in the amino acid coded for.
EXAMPLE:
CCG mutated to CCA would make mRNA GGC
become
GGU which is still
glycine
.
Slide762.
Missense
Mutation
-
altered
codon
still codes for an amino acid & makes sense although not necessarily the RIGHT sense
. (Make a protein, just not the correct one)
3.
Nonsense mutation -
Alterations that change an amino acid code to a stop
codon
. Almost always leads to a nonfunctional protein.
Slide774.
Insertions & deletions
are additions or losses of one or more nucleotide pairs in a gene.
a.
Note this can cause
missense
or nonsense.
Where
the
amino
acid is incorrect in a chain can be important or not.
Frameshift
mutation
- alters “reading frame” of message (# of nucleotides inserted or deleted is not a multiple of 3.
a. (
the big cat) remove the h =
teb
igc
at_.) This will make
all
amino acids downstream from this incorrect.
What can cause Mutations?:
Mutagens
- Physical & chemical agents that cause
mutations or increase the mutation rate.
Examples - X-rays, Radiation, UV light, chemicals (pesticides, radon), Viruses & Bacteria