Lecture 17: Cell cycle & Division; Sexual Reproduction & Meiosis

Cell division of eukaryotic somatic cells (body cells)

divide by mitosis

Cell division of prokaryotic cells

divide by binary fission

Cell division of eukaryotic gametic cells

divide by the process of meiosis

Eukaryotic cells divide by the process of

mitosis

How do cell’s know when to divide?

cell cycle is regulated by molecules to help cell prepare to divide

mitosis produces

identical cells

binary fission produces

identical offsprings

meiosis produces

gametic cells

Interphase

process that occurs before the cell split

Interphase takes up __ of process

3/4

checkpoints in mitosis

ensures each step is completed correctly

if a cell fail checkpoints…

apoptosis occurs

apoptosis

programed cell death

Cell cycle phases

G1, S, G2, M

G1 phase is the

first growth phase

G1 occurs during

interphase

G1 appears…

uneventful but is biochemically busy

Events during G1:

increasing metabolism, makes more atp, collects nucleotide to produce a copy of DNA, and makes many proteins

Cells in G1 do this more than the cells around them

cellular respiration

G1 checkpoint:

checks to ensure enough atp, correct proteins, and enough nucleotides are made

S phase is the

synthesis phase

S phase occurs during

interphase

Events of S phase:

DNA replicates to make 2 sister chromatids

sister chromatids

2 identical chromosomes held together by a centromer

When a cell divides to reproduce during mitosis, the 2 sister chromatids divide and

one is taken by the daughter and the mother keeps the other

G2 phase is the

second growth phase

G2 occurs during

interphase

G2 events:

replenishes energy, synthesizes proteins (for chromosome movement), some organelles duplicate, cytoskeleton is dismantled

G2 checkpoint:

ensures chromatids are made and checks for mutations

M phase is

mitosis

M phase is the process of

cell division

Mitosis forms

daughter cells that are genetically identical to each other and the parent

Mitotic stages

prophase, metaphase, anaphase, telophase w/ cytokinesis

Prophase events:

-nuclear envelope breaks down

-chromosomes condense

- spindle fibers begin to appear

-centrosomes begin to move to opposite poles

-spindle fibers attach to chromosomes and centrosomes

Metaphase events:

-spindle fibers develop

-centrosomes at opposite poles,

-chromosomes align in middle

-spindle fibers attach to sister chromatids

Anaphase events:

-sister chromatids are pulled apart by spindle fibers

-each chromatid becomes a chromosome

-spindle fibers are toward poles

Telophase events

-chromosomes arrive at opposite poles and start to decondense

-nuclear envelope reassembles

-mitotic spindle assembly breaks down

-cytokinesis finishes

cytokinesis

process that occurs during telophase that is the division of the cytoplasm

M checkpoint occurs during

metaphase

M checkpoint:

checks correct replication and ensures one chromatid is attached to one centrosome

G0 phase is the

zero stage

G0 phase:

not actively dividing

when cells lack nutrients or environmental issues can cause cells to

stay in G0

Binary fission produces organisms that are

genetically similar because no checkpoint check for mutations

What type of reproduction is binary fission?

asexual

Binary fission is

easier and faster to grow

Process for binary fission

chromosomes duplicate and separations of copies go to opposite ends of cell. Continued elongation of cell and movement of copies. it then divides into 2 daughter cells

Binary fission has no

checkpoints

Meiosis allows for

genetic variation

requirement for adaptation

change in environment

Meiosis occurs in

reproductive organs- testes and ovary produce spermocytes and oocytes

Meiosis produces what cells?

haploid and diploid

haploid cells

one set of chromosomes

Haploid cells are

eggs and sperm

Diploid cells

contain 2 copies of chromosomes; 1 from mother and 1 from father

example of diploid cells

humans

Overall goal of meiosis

genetic recombination and chromosome reduction

steps of meiosis

interphase, meiosis 1, meiosis 2

Meiosis 1 is the

first set

Prophase 1 events:

-nuclear envelope breaks down

-sister chromatids replicate

-chromosomes condenses to form pairs of homologous chromosomes

-spindle fibers start to appear

-centrosomes begin to move to opposite poles

Metaphase 1 events:

Independent assortment: random assortment of chromosomes at midline plate of cells.

Independent assortment is the

second mechanism to support genetic variation in meiosis

Anaphase 1 events:

sister chromatids are pulled apart by spindle fibers

-genetic variations=resulting gametes

telophase 1 events:

-chromosomes arrive at opposite poles and start to condense

-nuclear envelope reassembles

-mitotic spindle assembly breaks down

-cytokinesis

after telophase 1:

each cell is a now a diploid but with one set of 2 sister chromatids

End result of meiosis 2:

4 haploid cells

After meiosis, males are able to keep __ haploid cells

4

After meiosis, females are able to keep __ haploid cells

1

Barr bodies

have DNA but nothing else to be fully functional

The haploid cells females make:

1 fully functional and 3 barr bodies

Meiosis 2 is similar to

mitosis c

crossing over

exchange of chromosome segments between homologous nonsister chromatids and has no limit

crossing over occurs during

prophase 1

At the end of mitosis

2 diploid cells are produced