BIOL 2311 Lecture Notes - Lecture 11: Growth Factor, Motor Protein, Signal Transduction
CH 11 Meiosis
Mitosis: cell division, making copies of the cell
If parent cell is deployed, the daughter cell will be also deployed
Cell Division in Prokaryotes
Prokaryotic cell division occurs as binary fission in which cell divides into two halves.
Genetic information exists as a single, circular doublestranded DNA molecule (nucleoid).
Copying begins at replication origin, and proceeds bidirectionally.
One genome ends up in each daughter cell.
(in eukaryotes cell division occurs thru mitosis and cytokinesis)
Binary fission:
Ftsz ring protein:
FtsZ is a bacterial cytoskeletal protein that is essential for cell division in many prokaryotes.
•It has been shown to be a bacterial homolog of eukaryotic tubulin, based both on a low sequence
identity and a striking structural similarity.
•Just like eukaryotic tubulin, FtsZ polymerizes as well as binds and hydrolyzes GTP in a polymerization-
dependent manner.
•Actin-like protein also appears to be associated with FtsZ.
Eukaryotic Chromosomes
All eukaryotic cells store genetic information in chromosomes.
Most eukaryotes have between 10 and 50 chromosomes in their body cells.
Human cells have 46 chromosomes.
23 nearly-identical pairs
The DNA double helix in the cell nucleus is packaged by special proteins termed histones. Which form
small groups called nucleosomes and create a complex structure called chromatin- a protein/DNA
complex. The chromatin coils around to make up the chromosome.
Eukaryotic cell division -Portrait of a Chromosome
Primarily DNA and protein
Described by size and shape
Heterochromatin (dark)
Euchromatin (light)
Contains:
-Telomere
-Origin of replication sites
-Centromere
Composition of Chromosomes
Chromosomes are composed of a complex of DNA and protein, chromatin.
-heterochromatin - not expressed
-euchromatin - expressed
DNA exists as a single, long, double-stranded fiber extending the entire length of a chromosome.
forms nucleosome every 200 nucleotides
DNA coiled around histone proteins
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Packing DNA
DNA fits into a nucleus because it is packed into a shorter length by histone proteins
Other nonhistone proteins also associate with DNA; the complex of DNA and all its associated proteins is
chromatin
In a nucleosome, an eight-protein nucleosome core particle forms when DNA winds around the histones
H2A, H2B, H3, and H4
-- A short linker segment of DNA connects nucleosomes
Structure of nucleosome
Nucleosome:
-Complex of DNA and histone proteins
-Promote and guide coiling of DNA
-DNA duplex coiled around 8 histone proteins every 200 nucleotides
-Histones are positively charged and strongly attracted to negatively charged phosphate groups of DNA
Packing DNA (cont'd.)
Nucleosomes and linkers appear as beads on a string under electron microscopes
-The 10-nm chromatin fiber is named from the diameter of the beads and compacts DNA by a factor of
about 7
-Further packing occurs in the 30-nm chromatin fiber when the nucleosome and linker are bound by the
fifth histone protein H1
- The solenoid model predicts the nucleosomes spiral helically with about six nucleosomes per turn
-Chromatin packing continues at higher levels, with euchromatin being loosely packed and
heterochromatin showing dense packing
Solenoid model
Nucleosomes wrapped into higher order coils called solenoids:
- Leads to a fiber 30 nm in diameter
-Usual state of nondividing (interphase) chromatin
During mitosis, chromatin in solenoid arranged around scaffold of protein to achieve maximum
compaction:
-Radial looping aided by condensin proteins 12
Arrangement of chromosomes:
Karyotype - Individual’s particular array of chromosomes.
-diploid - A cell possessing two copies of each chromosome (human body cells- dad and mom).
Homologous chromosomes are made up of sister chromatids joined at the centromere.
Haploid - A cell possessing a single copy of each chromosome (human sex cells).
Research Method: Preparing a Human Karyotype
Chromosomes
The chromosome complement = the complete set of chromosomes of plants and animals.
The nucleus of each somatic cell contains a fixed number of chromosomes typical of the particular
species.
The number of chromosomes vary tremendously among species and have little relationship to the
complexity of the organism.
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Ploidy
-The number of chromosome sets in a cell or species is called its ploidy.
-Some microorganisms have only one copy of each type of chromosome in their nuclei – they are
haploid, or n.
-Many plant species, have three, four, or even more complete sets of chromosomes in each cell – They
are polyploid.
-Most eukaryotes have two copies of each type of chromosome in their nuclei – they are diploid, or 2n.
-The two chromosomes of each pair in a diploid cell are called homologous chromosomes – one is from
the mother, the other from the father.
-Homologous chromosomes have the same genes in the same order in the DNA of the chromosomes.
Replication of Chromosomes
Chromosomes must be replicated before cell division.
- Replicated chromsomes are connected to each other at the centromere
- cohesin – complex of proteins holding replicated chromosomes together
- sister chromatids: 2 copies of the chromosome within the replicated chromosome
The cell cycle:
Eukaryotic Cell Cycle
1. G1 (gap phase 1) Primary growth phase, longest phase
2. S (synthesis) Replication of DNA
3. G2 (gap phase 2) Organelles replicate, microtubules organize 4. M (mitosis) Subdivided into 5 phases
5. C (cytokinesis) Separation of 2 new cells
Cell cycle:
Cell division
A process in which one cell becomes two identical daughter cells.
-development
-renewal
-regeneration
Cell death
Apoptosis is a process of cell death in which cells signal their own demise in a programmed way.
-development
-response to abnormality
Cell cycle:
M phase
Mitosis is divided into 5 phases:
1. Prophase
2. Prometaphase
3. Metaphase
4. Anaphase
5. Telophase
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Document Summary
Mitosis: cell division, making copies of the cell. If parent cell is deployed, the daughter cell will be also deployed. Prokaryotic cell division occurs as binary fission in which cell divides into two halves. Genetic information exists as a single, circular doublestranded dna molecule (nucleoid). Copying begins at replication origin, and proceeds bidirectionally. One genome ends up in each daughter cell. (in eukaryotes cell division occurs thru mitosis and cytokinesis) All eukaryotic cells store genetic information in chromosomes. Most eukaryotes have between 10 and 50 chromosomes in their body cells. The dna double helix in the cell nucleus is packaged by special proteins termed histones. Which form small groups called nucleosomes and create a complex structure called chromatin- a protein/dna complex. The chromatin coils around to make up the chromosome. Chromosomes are composed of a complex of dna and protein, chromatin.
