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 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 cells volume
Slide 3
Ratio 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
Slide 4
Division 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
Slide 5
Slide 6
Cell 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
Slide 7
Slide 8
Chromosomes 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
Slide 9
Slide 10
The 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
Slide 11
The Cell Cycle
Slide 12
Slide 13
Events 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
Slide 14
Slide 15
Mitosis 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
Slide 16
Mitosis
Slide 17
Cytokinesis 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
Slide 18
Slide 19
Cytokinesis in Animal Cells
Slide 20
Controls 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
Slide 21
Cell 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
Slide 22
Cell Cycle Regulators
Slide 23
Uncontrolled Cell Growth Cancer is a disorder in which some of
the bodys 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
Slide 24
p53 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.
Slide 25
Slide 26
Uncontrolled Cell Growth
Slide 27
CHAPTER 13: MEIOSIS AND SEXUAL CYCLES Meiosis 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 MOST IMPORTANT - the cells
produced at the end of meiosis contain one chromosome of each
homologous (matching) pair.
Slide 28
GENE - HEREDITARY INFORMATION, IN A SECTION OF A DNA MOLECULE
ON A CHROMOSOME. LOCUS (LOCI) - A GENES 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.)
Slide 29
AUTOSOMES - 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 INDIVIDUALS 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.
Slide 30
THE HUMAN LIFE CYCLE: THE HUMAN LIFE CYCLE: ( characteristic of
most animals) Gametes are the only haploid cells. The diploid
zygote divides by mitosis producing a diploid organism.
Slide 31
MEIOSIS STEPS: MEIOSIS STEPS: ( FIG. 13.5.) (a) Each chromosome
replicates. (This shows 1 homologous pair). Remember - sister
chromatids & centromere. HAPLOID (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)
Slide 32
MEIOSIS 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.
Slide 33
COMPARING 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.
Slide 34
SUMMARY SUMMARY: differences between Mitosis &
Meiosis.
Slide 35
FIG. 13.8 genetic variation FIG. 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.
Slide 36
1st 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.
Slide 37
Crossing Over - produces individual chromosomes that combine
genes inherited from our two parents. Independent Assortment,
Random Fertilization, & Crossing Over Independent Assortment,
Random Fertilization, & Crossing Over - result ways that
genetic variation can be produced.
Slide 38
SUMMARY: 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?
Slide 39
CHAPTER 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.
Slide 40
JAMES WATSON JAMES WATSON CO-FOUNDER OF THE STRUCTURE OF DNA
Watson & Crick working on the DNA structure model. (April
1953)
Slide 41
Transformation 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.
Slide 42
EVIDENCE 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.
Slide 43
ADDITIONAL 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 Chargaffs
Rules. NOTE: All these discoveries were before Watson & Crick
discovered the double helix structure of DNA.
Slide 44
Structure 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.
Slide 45
Fig. 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. Whats a nm?
Slide 46
Notice the strands are oriented in opposite directions. This
entire structure was worked out by Watson & Crick in 1953 with
help from Rosalind Franklins x- ray diffraction photo of DNA
Slide 47
Base Pairing in DNA Base 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.
Slide 48
The SEMICONSERVATIVE MODEL - DNA replication model
Slide 49
Meselson & Stahl tested the three hypothesis's on DNA
replication
Slide 50
Beginnings of how DNA Replicates. DNA polymerase. Elongation of
DNA at a replication fork is catalyzed by a enzyme called DNA
polymerase. Rate of elongation in humans is approx.50/sec.
Slide 51
Adding 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.
Slide 52
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.
Slide 53
SYNTHESIS 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.
Slide 54
PRIMING 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.
Slide 55
Slide 56
FIG. 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
Slide 57
Enzymes 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 organisms
genes from being eroded through successive rounds of DNA
replication. Secret to aging?
http://www.youtube.com/watch?v=J9QApCHsrJk&feature=related
http://www.youtube.com/watch?v=J9QApCHsrJk&feature=related
Slide 58
Image of Telomere squeneces (yellow) on chromosomes
Slide 59
Chapter 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.
Slide 60
Basics 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.
Slide 61
mRNA 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.
Slide 62
Learn 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
Slide 63
Fig. 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).
Slide 64
3. 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.
Slide 65
RNA 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.
Slide 66
RNA 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.
Slide 67
Translation - 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
tRNAs deliver their amino acid, they add them to a growing
polypeptide chain. tRNAs are now available to pick up another amino
acid to repeat the process. 4) New Polypeptide chain added in the 5
to 3 direction.
Slide 68
The 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.
Slide 69
Fig. 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.
Slide 70
GTP & proteins called elongation factors needed to drive
this process.
Slide 71
Termination 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
Slide 72
Fig. 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.
Slide 73
Proteins 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.
Slide 74
Transcription & Translation in Bacteria: 1.Bacteria
(Prokaroytes) have no nucleus, so mRNA does not need to move
through the membrane to the ribosome. 2.Streamlined operations here
- Transcription & Translation can be occurring at the same
time. 3. There is not RNA processing in bacteria. (All exons).
Slide 75
MUTATIONS: MUTATIONS: 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.
Slide 76
2. 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.
Slide 77
4. 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. 5.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