Lecture 13 cell division and cell cycle Flashcards
Cell Theory:
one of the fundamental
principles of modern biology
Four major points to cell theory
1.All organisms are composed of cells or cell products.
2.All the cells in an organism have the “same” DNA
and number of chromosomes (unless they are sex
cells)
3.The chemical reactions characteristic of living
systems occur within cells.
4. All cells arise from pre-existing cells
Overview of Cell Division
key roles of cell division
Key Roles of Cell Division:
* Cells reproduce via cell division
– Reproduction
* Unicellular organisms
– Growth/Development
* Multicellular organisms
– Cell repair/regeneration
Overview of Cell Division
cell division is what process?
Cell division is the process by which a single cell becomes two daughter cells
cell division involves division of?
Cell division involves division of the nucleus and cytoplasm
Karyokinesis
Division of nucleus
Cytokinesis
– division of cytoplasm via formation of cleavage furrow
Requirements for successful cell division
1.Full complement of DNA must be distributed to the two
daughter cells from single parent cell
2.Parent cell must be large enough to divide in two and still contribute cytoplasmic components to each
daughter cell
Methods of Cell Division:
– Binary fission
-Mitosis
– Meiosis
Binary fission
* Asexual reproduction
* New copy may be identical or have mutations
* Prokaryotes (e.g. Bacteria) and other single-celled organisms
(Amoebae, Paramecia etc.)
– Mitosis
* Somatic cells
* Produces exact copies of parental chromosomes
– Meiosis
* Makes sexual reproduction possible!
* Produces daughter cells (gametes) with half the number of
chromosomes compared to parent cell
* Not exact copies
Methods of Cell Division:
-Binary fission
-Mitosis
-Meiosis
Binary Fission
Asexual reproduction
* New copy may be identical or have mutations
* Prokaryotes (e.g. Bacteria) and other single-celled organisms
(Amoebae, Paramecia etc.)
Methods of Cell Division:
-Binary fission
-Mitosis
-Meiosis
Mitosis (somatic cells(body cells) which are diploids 2n) eukaryotic cell division
- Somatic cells (diploid (2n))
- Produces exact copies of parental chromosomes
Methods of Cell Division:
-Binary fission
-Mitosis
-Meiosis
Meiosis-gametes(sex cells) n haploids
Makes sexual reproduction possible!
* Produces daughter cells (gametes) with half the number of chromosomes compared to parent cell
* Not exact copies!
Prokaryotic Cell Division
Binary Fission
Replication of DNA? two important regions on DNA?
DNA segregation
Ctyokinesis
Binary Fission
Most bacteria - one circular
chromosome, highly folded and coiled
* Replication of DNA:
Cell increases in size
Two important regions on DNA
Origin of replication, and Terminus of replication
* DNA segregation:
Two origins (attached to plasma
membrane) move apart
* Ctyokinesis:
Pinching in of plasma membrane;
synthesis of new cell wall materials
Eukaryotic Cell Division
Mitosis
Result?
Why?
Result - two identical daughter cells with same
number of chromosomes as parent
– Still involves general steps seen in binary fission but more complex than in prokaryotes!
Why?
Prokaryotes- no nucleus, single circular DNA
Eukaryotes- nucleus–>karyokinesis, many linear chromosomes
Eukaryotic Cell Division – Cell Cycle
Two Distinct stages
Cell division proceeds
through a number of
steps that make up
the cell cycle
Two distinct stages:
– M phase: the time
during which the
parent cell divides
into two daughter
cells (mitosis and cytokinesis)
– Interphase: the time
between two
successive M phases
phases:
* G1 (Preparation for DNA synthesis)(DNA polymerase, helicase primase, ligase)
* S (DNA synthesis)(DNA replication)(DNA duplication)
* G2 (Preparation for mitosis and cytokinesis)
G0 phase- cells that are not actively dividing
Example:
– Not all body cells
actively participate in
cell cycle
Many cells pause
between M and S phase
G0 cells remain active in
other ways
- E.g. liver cells metabolize
and detoxify - E.g. nerve cells enter G0
permanently
Mitotic Cell Division (Eukaryotes)
Chromosome Structure
In eukaryotic cells,
DNA is organized
with histones and
other proteins into
chromatin
Chromatin can be
looped and
packaged to form
chromosomes
Mitotic Cell Division (Eukaryotes)
In humans
human karyotype
Karyotype:
The portrait formed by the
number and shapes of
chromosomes representative of a species is called its karyotype
In humans:
* Somatic cells – 46 chromosomes
* Gametes – 23 chromosomes
Human karyotype:
* 22 pairs of homologous
chromosomes (autosomes)
* 1 pair of sex chromosomes (X and Y)
Mitotic Cell Division (Eukaryotes)
Homologous Chromosomes
Number of complete chromosome sets is called?
Two of the same type of chromosome is called?
Two of the same type of chromosome = homologous
chromosomes
* Each carries same set of
genes
* One homologue is paternal
chromosome
* The other homologue is
maternal chromosome
Number of complete
chromosome sets = ploidy
* Haploid (n) vs. Diploid (2n)
Mitotic Cell Division (Eukaryotes)
Homologous Chromosomes and Sister Chromatids:
– For cell division to proceed normally, every
chromosome in parent cell must be duplicated so each
daughter cell gets a full set of chromosomes
– During which phase of the cell cycle does duplication
occur? s phase
- After duplication of DNA, each chromosome is made
up of two sister chromatids
After Duplication of DNA
each chromosome is made
up of two sister chromatids
Mitotic Cell Division (Eukaryotes)
Homologous Chromosomes and Sister Chromatids
how are sister chromatids are held together?
count the nuber of chromosomes?
Sister chromatids are held together at centromere
* to count the number of chromosomes count the centromeres
Haploid vs. Diploid
Haploid (n): one copy of each chromosome (non homologous chromosomes)
Diploid (2n): two copies of each chromosome (homologous chromosomes)
somatic cell
any cell in body that contains diploid number of chromosomes
gamete
are haploid cells, carries only one copy of each chromosome
to count the amount of chromatids
count chromosomes (centromeres) then multiply by 2 to get chromatids
Explore mitosis
Mitosis steps?
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
In mitosis interphase can you distinguish specific chromosomes?
No you cannot distinguish specific chromosomes because they are all long and thin
Mitosis Prophase
what are the mitotic spindle made up of?
Microtubules
what is the significance of the centrosome?
1) prophase: chromosomes condense, centrosomes radiate microtubules and migrate to opposite poles
Mitosis
1. Prophase
2. Prometaphase
3. Metaphase
4. Anaphase
5. Telophase
- Prophase
2.Prometaphase
1)Prophase
-chromosomes condense, centrosomes radiate microtubules and migrate to opposite poles
-Sister chromatids joined
together by cohesions(proteins)
2.Prometaphase
-Microtubules of the mitotic spindle attach to chromosome’s
-nuclear membrane break-down
-spindles attach to chromosomes (kinetochores)
-Microtubules polymerize and
depolymerize
Kinetochores look like?
-Protein complexes
-Each kinetochore
associated with one of
sister chromatids
-Attachment site for single
spindle microtubule
Mitosis
1. Prophase
2. Prometaphase
3. Metaphase
4. Anaphase
5. Telophase
3.Metaphase
4.Anaphase
Metaphase: chromosomes align in center of cell, alignment of chromosomes at metaphase plate
Anaphase: Sister chromatids(which become individual chromosomes when the centromere splits separate and travel to opposite poles
- Sister chromatids
separate
– Cohesin proteins
cleaved - Non-kinetochore
microtubules - Chromatids->chromosomes
*equal segregation of chromosomes
Mitosis
1. Prophase
2. Prometaphase
3. Metaphase
4. Anaphase
5. Telophase
5.Telophase
*can be followed by cytokinesis
Telophase: Nuclear envelope re-forms and chromosomes decondense
Cytokinesis (animals)
actin, contractile ring, cleavage furrow
cytokinesis(plant)
phragmoplast, vesicles, cell plate
Result: two diploid cells; genetically identical to parent cell
