01 Cell Reproduction
-
Upload
martin-jellinek -
Category
Education
-
view
1.851 -
download
2
description
Transcript of 01 Cell Reproduction
BINARY FISSION IN BACTERIA
Much faster than mitosis in eukaryotic cells
Takes approx. 20 mins as opposed to several hours
If resources were available once cell could become 16,000,000 in 8 hours!
BINARY FISSION IN BACTERIA
BINARY FISSION IN BACTERIA
Bidirectional replication of circular DNA
BINARY FISSION IN BACTERIA
DNA moves to poles
BINARY FISSION IN BACTERIA
Cell elongates
Cleavage furrow forms
BINARY FISSION IN BACTERIA
Cell divides
THE CELL CYCLE – EUKARYOTIC CELLS
Final checkpoint at the end of metaphase
ANIMATIONS
Animation 1
Animation 2
THE CELL CYCLE – G1
The first phase is a growth phase (G1) The new cell starts growing and
replicating its organelles At the end of G1, the checkpoint is to
gauge if it is a good time for cell to keep growing or dividing or if a delay is necessary.
If the cell is under any sort of stress, it will pause at this stage.
THE CELL CYCLE - S
During the synthesis (S) phase, DNA replication occurs It is at this point that the diploid cell (2n) doubles to 4n, so
that when it divides there will be two complete copies of the DNA
DNA replication is semi-conservative – every new molecule consists of one original strand and one new strand.
DNA replication involves numerous enzymes Helicase and gyrase unwind and unzip to strands of DNA DNA polymerase continuously adds nucleotides to the leading
strand in a 5’ to 3’ direction RNA primase makes an RNA primer on the lagging strand DNA ligse sticks together prefabricated ‘Okazaki’ fragments
made by DNA polymerase to replace the RNA
THE CELL CYCLE – G2
During the next growth phase (G2), the cell continues to grow in preparation for division
The checkpoint during this phase is extremely important.
If any errors have occurred during transcription, the cell must undergo apoptosis (programmed cell death)
THE CELL CYCLE - M
During Mitosis (M), the single parent cell gives rise to two identical daughter cells.
Another checkpoint occurs at the end of metaphase to ensure that chromosomes are aligned and that spindle fibres are attached corectly.
A negative result at the checkpoint here will result in apoptosis.
THE CELL CYCLE - C
Cytokynesis (C) is actually the last part of Mitosis
At this point the cell, which momentarily has twin nuclei, will divide in to two new cells (2n) and the process will begin again.
WHAT HAPPENS IF THE CHECKPOINTS DON’T WORK?
If cell cycle checkpoints are operated by enzyme proteins.
These enzymes can be prevented from carrying out normal function by inhibitors.
These enzymes could also be stimulated to maintain an active state permanently.
Either way can lead to uncontrolled and unmonitored cell division, this is commonly known as ….
CANCER
Cells multiply uncontrollably and regardless of accumulating errors will never apoptose.
Does not form useful cells as cells spend far more time in division rather than growth (a reversal of the normal situation).
MITOSIS
INTERPHASETHE CELL PREPARES FOR DIVISION
Animal & Plant Cells Nucleus clearly
defined Chromosomes not
yet visible
DNA replicated Organelles
replicated Cell increases in
size
INTERPHASE
Animal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
PROPHASETHE CELL PREPARES FOR NUCLEAR DIVISION
Animal & Plant Cells DNA packaged in
to chromosomes Nuclear envelope
disappears
Centrioles move to opposite sides of the cell
PROPHASE
Animal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
METAPHASETHE CELL PREPARES CHROMOSOMES FOR DIVISION
Animal & Plant Cells Chromosomes
line up at the center of the cell
Spindle fibres attach to centromeres on the chromosomes
Centrioles reach the opposite poles of the cell
METAPHASE
Animal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
ANAPHASETHE CHROMOSOMES DIVIDE
Animal & Plant Cells Spindle fibers
contract and pull chromosomes apart
½ of each chromosome (called a chromatid) moves to each hemisphere
Unattached spindle fibres push against each other or the sides of the cell, and it begins to elongate
ANAPHASE
Animal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
TELOPHASETHE CYTOPLASM DIVIDES
Animal Cell DNA spreads out 2 nuclei form Contractile ring
causes a cleavage furrow to form the 2 new daughter cells
Plant Cell DNA spreads out 2 nuclei form Cell plate forms
new cell wall between the nuclei to form the 2 new daughter cells
TELOPHASE
Animal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
MITOSIS ANIMATIONS
Mitosis.exe
Mitosis Animation
Animal Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Plant Mitosis -- ReviewInterphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
SUMMARY OF MITOSIS
Prophase: Chromosomes condense Nuclear envelope disappears centrosomes move to opposite sides of the cell Spindle forms and attaches to centromeres on the
chromosomes
Metaphase Chromosomes lined up on equator of spindle centrosomes at opposite ends of cell
Anaphase Centromeres divide: each 2-chromatid chromosome
becomes two 1-chromatid chromosomes Chromosomes pulled to opposite poles by the spindle
Telophase Chromosomes de-condense Nuclear envelope reappears Cytokinesis: the cytoplasm is divided into 2 cells
MEIOSIS
RECOMBINATION THROUGH MEIOSIS
DNA replicates Crossing over
Random assortment
First division
Second random assortment
Second division
MITOSIS VS. MEIOSIS
GETTING THE NAMES RIGHT
Kinetochore
Centromere
Sister chromatids
Spindle fibres / microtubules
RECOMBINATION = VARIATION
2 pairs of chromosomes = 4 possibilities 4 pairs of chromosomes = 8 possibilities What are the chances of identical offspring?
2n = 46 (not incl. twins) 1 / 16,777,216
DNA Replication
DNA is uncoiled and unzipped by helicase & gyrase
The original strands are called the template strands
The new strands are called the complementary strands
The 3’ to 5’ template strand is the leading strand
The 5’ to 3’ template strand is the lagging strand
The complementary strand can only be written 5’ to 3’
DNAi ANIMATIONS x 2
The leading strand
An RNA primer is put down by RNA polymerase
Complementary DNA is put down base-pair by base-pair by DNA polymerase
3’ 5’
5’ 3’
Rp Dp
DIRECTION OF REPLICATION
The lagging strand
RNA polymerase puts down primers along the template strand of DNA
DNA polymerase III builds short ‘Okazaki’ fragments from each primer
DNA polymerase I removes the RNA and replaces it with DNA
DNA ligase sticks the fragments together
The lagging strand
5’ 3’
3’ 5’
RNA Polymerase
DNA Polymerase III
DNA Polymerase I
DNA Ligase
DIRECTION OF REPLICATION
ADDITIONAL INFO ON CELL REPRODUCTION
Our cells can be categorised in to two types Somatic cells (diploid) Germline cells (diploid but give rise to
haploid gametes – sperm & eggs)
Biozone Fun! DNA replication
pp. 203-25 Cell cycle, mitosis, apoptosis
pp. 209-212 Meiosis
pp. 287-290