Bacterial Cell Division

· Bacteria divide by binary fission

· No Sexual life cycle

· Reproduction is Donal

· Single, circular bacterial chromosome is replicated

Bacterial Cell Division

· Replication begins at the origin of replication and proceeds in two directions to site of

termination

· New chromosomes are partitioned to opposite ends of the cell

· Septum forms to divide the cell into two cells

EUKARYOTIC CHROMOSOMES

· Eukaryotes typically have 10 to 50 chromosomes in their body (somatic)cells

· Humans have 46 chromosomes in 23 nearly identical pairs

· Additional/missing chromosomes usually fatal

· Humans are diploid (2n)

· Two complete sets of chromosomes

· 46 total chromosomes

· Haploid (n)

· One set of chromosomes

· 23 in humans

EUKARYOTIC DNA IS ORGANIZED INTO CHROMOSOMES

· DNA of a single chromosome is one long continuous molecule

· Typical human chromosome 140 million nucleotides long. Average length is 4. 3cm

· Is compacted to varying degrees within a cell

· A chromosome is a complex of DNA and histone proteins

· Histone is positively charged

· DNA is negatively charged

REPLICATION

· Prior to replication, each chromosome composed of a single DNA molecule

· After replication, each chromosome composed of 2 identical DNA molecules

· Visible as 2 strands connected in middle as chromosome condenses more

· One chromosome composed of 2 sister chromatids held together by cohesion proteins

· Pair of chromosomes are homologous -Each is a homologous

EUKARYOTIC CELL CYCLE

Interphase

· G(gap phase 1)

↳ primary growth phase, longest phase

· S (synthesis

↳ Replication of DNA

· G2 (gap phase 2)

↳ Organelles replicate, microtubules organize

· M (mitosis (

↳ Subdivided into 5 phases

· C (cytokinesis)

↳ Separation of 2 new cells

INTERPHASE

· G, S, and G2 phases

· G2-cells undergo major portion of growth

· S-replicate DNA

· G2-chromosomes coil more tightly using motor proteins; centrioles replicate

· Centromere -point of constriction

· Each Sister chromatid has a centromere

MPHASE

· Mitosis is divided into five phases:

· Prophase

· Prometaphase

· Metaphase

· Anaphase

· Telophase

PROPHASE CELLULAR ORGANIZATION

· Individual condensed chromosomes first become visible with the light microscope

· Condensation continues throughout prophase

· Spindle apparatus assembles

· Two centrioles move to opposite poles forming spindle apparatus (no centrioles in

plants)

· Nuclear envelope breaks down

PROMETAPHASE

· Transition occurs after disassembly of nuclear envelope

· Microtubule attachment

· 2nd group grows from poles and attaches to kinetochores

· Each sister chromatic connected to opposite poles

· Chromosomes begin to move to center of cell

METAPHASE

· Alignment of chromosomes along metaphase plate

· Not an actual structure

· Future axis of cell division

· Without proper alignment, chromosomes won't separate correctly

ANAPHASE

· Begins when centromeres split

· Sister chromatids pulled to opposite poles

TELOPHASE

· Spindle apparatus disassembles

· Nuclear envelope forms around each set of sister chromatids

· Now called chromosomes

· Chromosomes begin to uncoil

· Nucleolus reappears in each new nucleus

CYTOKINESIS

· Cleavage of the cell into equal halves

· Animal cells -constriction of activ filaments produces a cleavage furrow

· Plant cells -cell plate forms between the nuclei

CONTROL OF THE CELL CYCLE

· Cell cycle has two irreversible points:

· Replication of genetic material

· Separation of the sister chromatics

· But it can be put on hold at specific points called checkpoints

· Process is checked for accuracy and can be halted if there are errors

· Allows cell to respond to internal and external signals

GROWTH FACTORS

· Act by triggering intracellular signaling systems.

↳ EX. Platelet derived growth factor (PDGF)

· PDGF receptor is a receptor is a receptor tyrosine Kinase (RTK)that initiates a MAP

Kinase cascade to stimulate cell division

Growth factors can override cellular controls that otherwise inhibit cell division