Upload
bayan-al-ghadeer
View
291
Download
4
Embed Size (px)
Citation preview
Cell DivisionCell DivisionMitosis- Cell reproductionMitosis- Cell reproduction
Learning Objectives
• The cell cycle and its phases.
• The cell division “mitosis”.
• Cell cycle control system.
• The different abnormalities of cell cycle (cancer).
• DNA structure and DNA replication .
Key Words• Chromosome• chromatin• centriole & centrosome• centromere & kinetochore• chromatid
Bayan Al-Ghadeer Dalal Al-Anazi
chromosome
A chromosome is a long, continuous piece of DNA which contains the genetic information for a cell.
Bayan Al-Ghadeer Dalal Al-Anazi
chromatin
Chromatin is the building block for a chromosome. It consists of DNA and proteins.
Bayan Al-Ghadeer Dalal Al-Anazi
Centriole & centrosome
A centriole is a barrel microtubule structure. Two centrioles arrange themselves perpendicularly to form a centrosome.
Bayan Al-Ghadeer Dalal Al-Anazi
centromere & kinetochore• The centromere is constricted region of the
chromosomes that holds the sister chromatids together, the site where kinetochore forms.
• The kinetochore is a complex protein containing structure to which microtubules attach.
Bayan Al-Ghadeer Dalal Al-Anazi
chromatid Is a one strand of the chromosome after it has duplicated for cellular division. The two chromatids are called “sister chromatids” and will eventually split and move to opposite ends of the cell.
Sister chromatids
Bayan Al-Ghadeer Dalal Al-Anazi
Ready?Let’s begin
Bayan Al-Ghadeer Dalal Al-Anazi
Cell division
Bayan Al-Ghadeer Dalal Al-Anazi
Why do cells divide?
•Growth
•Repair and replace dead cells
•asexual reproduction
Bayan Al-Ghadeer Dalal Al-Anazi
THE CELL CYCLE______________________
_
• Define cell cycle: the cell cycle is the sequence of growth and division of a cell. It consists of three major phases:
o interphaseo mitosiso cytokinesis.
• Cell division results in two cells that are both identical to the parent cell.
Bayan Al-Ghadeer Dalal Al-Anazi
Interphase
Estimated (90% of cycle) 3 phases
•G1 phase
•S phase
•G2 phase
Bayan Al-Ghadeer Dalal Al-Anazi
• Growth of cell.
• Dupliction of organelles.
• Synthisis of proteins.
G1 phase
Bayan Al-Ghadeer Dalal Al-Anazi
• DNA synthesis occurs• DNA replication results in
duplicated chromosomes• centrosome cycle
S phase
Bayan Al-Ghadeer Dalal Al-Anazi
• Cell continues to grow and if a problem
occurs in DNA replication, it will be repaired.• Cell will prepare for mitosis. • cell synthesizes proteins needed for cell
division
G2 phase
Bayan Al-Ghadeer Dalal Al-Anazi
Estimated (10% of cycle) Includes 2 parts :
1)Mitosis•Prophase•Promataphase
•Metaphase
•Anaphase
•Telophase
2) Cytokinesis
M phase
Bayan Al-Ghadeer Dalal Al-Anazi
Mitosis
• is the process in which a eukaryotic cell separates the chromosomes in its cell nucleus, into two identical sets in two daughter cells.
Bayan Al-Ghadeer Dalal Al-Anazi
Prophase
Duration (15 min)
• Chromosomes condense (get thicker) and coil, they become visible under light microscope.
• The two sister chromatids of each chromosomes attach at a point called centromere.
• Spindle fibers begin to form from two centrosome, and they will start moving apart.
Bayan Al-Ghadeer Dalal Al-Anazi
Duration (15 min)
• The nuclear membrane disappears.
• Kinetochores will get attached to the centromere.
• The spindle fibers become attached to the kinetochore.
Prometaphase
Bayan Al-Ghadeer Dalal Al-Anazi
Duration (20 min)
• Chromosomes reach their most highly condensed state.
• The spindle fibers begin to contract to the centromeres of the chromosomes, which are now arranged along the middle of the spindle.
Metaphase
Bayan Al-Ghadeer Dalal Al-Anazi
Duration (3 min)• The centromere of each
chromosome splits, allowing the sister chromatids to separate.
• The chromatids are then pulled by the spindle fibers toward opposite sides of the cell.
• The two sets of chromosomes are identical.
• Cleavage furrow starts to form.
Anaphase:
Bayan Al-Ghadeer Dalal Al-Anazi
Duration (10 min)• New nuclear membranes are formed
around each of the two sets of 46 chromosomes.
• The spindle fibers disappear.
• Chromosomes become thinner.
• Cytoplasm starts dividing by contractile ring.
• At the end, we will have two diploid daughter cells, which are identical.
Telophase:
Bayan Al-Ghadeer Dalal Al-Anazi
Cytokinesis
• the division of the cytoplasm and organelles
• Begin in anaphase and completed by the end of telophase .
Bayan Al-Ghadeer Dalal Al-Anazi
Summary
• Interphase (90% of cycle) o G1 phase~ growth o S phase~ synthesis of DNA o G2 phase~ preparation for
cell division• Mitotic phase (10% of cycle)o Mitosis~ nuclear divisiono Cytokinesis~ cytoplasm
division
Bayan Al-Ghadeer Dalal Al-Anazi
Cell cycle control system
Cell cycle control system Involves
•Cell cycle checkpoints
•Specialized protein complex
Function control the order and timing of the cell cycle.
Bayan Al-Ghadeer Dalal Al-Anazi
( control points ) They are pathways that:•Ensure that events are completed correctly before letting the cell enter the next phase.
The checkpoint receive signals from :
inside and outside the cell
Checkpoints
Bayan Al-Ghadeer Dalal Al-Anazi
There are 3 major checkpoints :I.at the end of G1 it is large & strong enough to continue with the cell division process
II.at the end of G2
III. during mitosis phase it ensures if the spindles attached to the kinetochore within each chromosome
Checkpoints
Bayan Al-Ghadeer Dalal Al-Anazi
Is a combination of a Cycline & Cdk*
to preform its work ( help the cell to enter the next phase) it has to be activated by phosphorylated at one site and dephosphorylated at the other site. * Cycline dependent kinase
Specialized protein complex
Bayan Al-Ghadeer Dalal Al-Anazi
Now we’ll see how much you’ve learned
so raise your handand wait your turn...
Bayan Al-Ghadeer Dalal Al-Anazi
Cell Cycle
MITOSIS
interphase
prophase
metaphase
anaphase
telophase
cytokinesis
Chromosomes invisible; DNA replicates
Chromosomes appear, nucleus disappears
Chromatids pulled to poles
Cytoplasmic division
Chromosomes at equator, spindle forms
Chromatids at poles, nucleus reforms
Bayan Al-Ghadeer Dalal Al-Anazi
Cell Increase and Decrease
• Cell division:oMitosis oCytokinesis
• Apoptosis (cell death) decreases the number
of cells.• Both cell increase and apoptosis occur
during normal development and growth.
Bayan Al-Ghadeer Dalal Al-Anazi
Abnormal Division
• If there is a damage in DNA during G1 and the P53 is not present, the cell can’t stop entering into the next phase so, it will complete the cycle in an abnormal way.Then the cycle will be uncontrolled .
• If a cell has extra protein BCL2 then it can absorb all of the death signals so the cell will prevent death(apoptosis) .That will leads to a high rate of mutation and the production of cells that tend to become cancerous ( tumor ) .
Abnormalities
Bayan Al-Ghadeer Dalal Al-Anazi
http://www.youtube.com/watch?v=vKIRWY-LMYc
• The uncontrolled growth of cells in human to the
disease called cancer.
http://www.youtube.com/watch?v=vKIRWY-LMYc
• The uncontrolled growth of cells in human to the
disease called cancer.
DNA
• Before:– Chromosome duplicates = 2 sister chromatids
(DNA replication )
• During:– Sister chromatids separate
• After:– 2 “daughter” cells– Genetically identical
DNA & Mitosis
Bayan Al-Ghadeer Dalal Al-Anazi
DNA structure
• Two strands coiled called a double helix.
• Center made of nitrogen bases bonded together by weak hydrogen bonds.
• Stands for deoxyribonucleic acid made up of subunits called nucleotides.
Bayan Al-Ghadeer Dalal Al-Anazi
constituents of nucleotide
Bayan Al-Ghadeer Dalal Al-Anazi
• Phosphate group
• 5-carbon sugar
• Nitrogenous base
Nucleotide made of:
Bayan Al-Ghadeer Dalal Al-Anazi
Anti-parallel Strands
•One strand of DNA goes from 5’ to 3’
•The other strand is opposite in direction going 3’ to 5’
Bayan Al-Ghadeer Dalal Al-Anazi
DNA Replication
Models of DNA replicate?“Possibilities”
In this model , one daughter molecule
contains both parental DNA strands, and the
other daughter molecule contains DNA strands of
all newly-synthesized material.
In this model two DNA double helices, both of which consist of one parental and
one new strand.
In this model the parental double helix is
broken into double-stranded DNA segments .The
segments assemble into complete DNA double helices from new and
parental strandsBayan Al-Ghadeer Dalal Al-Anazi
1. The DNA strands are separated at a specific area called origin .
2. The complementary strands are synthesized by DNA polymerase .
3. Termination : DNA polymerase goes throughout each strand in order to find errors and correct them.
Steps of DNA replication
Bayan Al-Ghadeer Dalal Al-Anazi
Base pairing During Replication
Enzymes Required for Replication• Helicase: an enzyme that catalyzes the energy-dependent
unwinding of the DNA double helix during DNA replication.
• DNA polymerase: an enzyme that catalyzes the assembly of deoxyribonucleoside triphosphates into deoxyribonucleic acid, with single-stranded DNA serving as the template. The enzyme is often found in tumor cells.
• Ligase : Joins together small newly synthesized pieces of DNA called Okazaki fragments.
• Primase : Adds an RNA primer so that DNA synthesis can begin
Bayan Al-Ghadeer Dalal Al-Anazi
Bayan Al-Ghadeer Dalal Al-Anazi
Abnormal division• What happens when DNA is damaged? DNA Structure• constituents of nucleotides. DNA Replication • Models of DNA replication.• Steps• Enzymes Required for Replication.
Summary
Bayan Al-Ghadeer Dalal Al-Anazi
• Essential cell biology – third edition
• http://www.biologie.uni-hamburg.de/b-online/library/falk/cellDivision/division.htm
• http://www.phschool.com/science/biology_place/biocoach/dnarep/classical.html
References