cell division and cell cycle

What does the term "diploid" mean?

2 chromosomes of each type (homologous pairs)

What cells are diploid?

Somatic cells

Abbreviation of diploid

2n

if 2n is replicated, we will get

4C

What does haploid mean?

one set of chromosomes 1C

abbreviation of haploid

n

what is meiosis?

cell division by which germ cells are produced

what are germ cells?

sex cells (ovum and sperm = gametes)

what are parent cells called in meiosis?

primitive germ cell

what happens to the genetic material in meiosis?

Reduction in amount of genetic material in which primitive cells containing 2n will be reduced to 1n

what process in meiosis results in genetic diversity?

cross over

where are primitive germ cells only found?

testes and ovaries

how many nuclear divisions occur in meiosis?

2; meiosis I and meiosis II
only one includes replication of dna (S phase only in first round)

what is the short gap between meiosis 1 and meiosis 2 called?

interkinesis

what happens during interkinesis?

no dna replication, only centrioles are replicated

When does a zygote form?

G1 phase of mitosis

describe interphase of meiosis

-identical to mitosis interphase

Prophase 1:

-Chromosomes become visible
- nuclear envelope breaks down
-crossing-over occurs

how do chromosomes appear in prophase 1 ?

maternal and paternal homologous chromosomes come close and ALIGN = TETRAD

the process of alignment happening in prophase 1 is called ________ by a structure called _________

synapsis ; synaptonemal complex

what are chiasma?

-remainder of synaptonemal complex.

- points of interchange by crossing over

what is crossing over?

the exchange of chromatids between homologous chromosomes, resulting in a mixture of parental characteristics in offspring.

what are the homologous paired chromosomes connected by in metaphase 1?

terminal chiasma

what happens in metaphase 1?

-Paired homologous chromosomes line up across the equatorial plate
-paired chromosomes connect by terminal chiasma
-mitotic spindle fibers connect the centromere of each chromosome to one side of cell

at what point do spindle fibers attach to centromere?

kinetochore

describe anaphase 1

-terminal chiasma disappears
-centromere does NOT divide = sister chromatids of the tetrad move together
-migration and arrival of new chromosomes to opp poles of cell

how does the movement of chromosomes occurs?

-shortening of spindle microtubules and kinetochore

at what end do spindle fibers become shorter in anaphase 1?

negative end -ve

describe telophase 1?

-cytokinesis
-chromosomes changed to chromatin
-nuclear envelope forms
-nucleolus reappears

how does cytokinesis happen?

contraction of actin around center of cells

what is the product of meiosis 1?

2 haploid daughter cells (1n) (23 chromosomes = 46 chromatids)
and (2C) DNA

how do we count chromosomes?

By the number of centromeres
(23 chromosomes could mean 23 chromatids or 46 chromatids )

what is the difference between meiosis 1 and meiosis 2?

-no S phase (no dna replication) in meiosis 2
-chromatids of chromosomes not identical in meiosis 2
-no crossing over in meiosis 2
-2 cells with genetic variation from parent cell

prophase 2:

Chromosomes condense, spindles form in each new cell, and spindle fibers attach to chromosomes
-no cross over

metaphase 2:

Chromosomes line up at the equator.
-single pair of chromosomes (not tetrad)

anaphase 2:

sister chromatids separate

telophase 2:

-A nuclear membrane forms around the chromosomes in each of the 4 new cells.
-cytokinesis

product of meiosis 2

4 daughter cells 1n , 1C

product of mitosis

2 daughter cells , 2n 2C

What are the 4 phases of the cell cycle?

M phase, G1 phase, S phase, G2 phase

M phase

mitosis and cytokinesis - chromosomal condensation and separation (mitosis)

G1 phase

The first gap, or growth phase, of the cell cycle, consisting of the portion of interphase before DNA synthesis begins. (presynthesisgap)

S phase

The synthesis phase of the cell cycle; the portion of interphase during which DNA is replicated. (DNA synthesis phase)

G2 phase

The second growth phase of the cell cycle, consisting of the portion of interphase after DNA synthesis occurs. (postsynthesisgap phase)

G1, S, G2 are collectively called

interphase

Normal cell functions happen during

interphase

Non-dividing cells are in what stage of the cell cycle?

G0

Examples of cells that are arrested in G0 phase?

Heart muscle and neuron cells

Why are neuron and cardiac cells called noble cells?

when lost, we cannot regenerate them

Why do we have more neuron cells than we need at birth?

neuron cells are in G0 phase = cannot divide.
We lose some neurons throughout life so we have to have spare cells

which cells perform mitosis?

somatic cells

Which is shorter, mitosis or interphase?

mitosis

Which cells take very short time in cell cycle?

RBCs and epithelial cells (specially of oral mucosa)

Why does it take longer to heal wounds when sick?

cell division affected by immunity

Which cells have a very long cell cycle?

WBCs- live for very long too

During interphase, describe morphology of cells (normal functioning)

-nucleus and nucleolus present
-nuclear membrane present
-chromatin not chromosomes

what happens during G1?

new cell synthesizes materials needed for cell growth (proteins, lipids, and carbs). prepares to replicate DNA

what happens during S phase?

DNA replication and centriole duplication

what happens during G2?

synthesis of special proteins (tubulin and actin) to build mitotic spindle fibers

2 main processes happen during mitosis:

1- Nuclear division (division of DNA)
2- Cytoplasmic division (cytokinesis)

What are the products of mitosis?

2 daughter identical cells

In order for a cell to divide successfully, the cell must first

1- Replicate DNA (S phase)
2- Give exactly one copy to each daughter
3- Pinch cell membrane w/out creating holes

Phases of Mitosis:

Please - Prophase
Make - Metaphase
A - Anaphase
Taco - Telophase

What happens during Prophase?

1- chromatin condenses to visible chromosomes
2- spindle fibers begin to form
3-Migration of 2 pairs of centrioles to opp sides
4- thinning and gradual disappearance of nuclear envelope
5- mixing nucleolus with rest of nucleus

what are spindle fibers made of?

microtubules = tubulin (made during G2)

What happens during Metaphase?

-alignment of all chromosomes at the middle of the cell (metaphase plane)
- Nuclear membrane completely disappears
- Attachment of spindle fibers to centromere of chromosome

what is the middle of the cell also called?

equatorial plane of cell (metaphase plane)

What marks beginning of metaphase?

Complete dissolving of nuclear membrane

At what point do spindle fibers attach to centromere?

Kinetochore (allows centromere to move up and down)

Difference between centromere and kinetochore?

Centromere: between 2 chromatids
Kinetochore: between spindle fiber and centromere

What is Anaphase marked by?

splitting of chromosome centromeres = chromosome halves (chromatids) drawn to opposite cell poles
(only splitting and moving, not reached the end yet. When reached, telophase has started)

how does the movement of chromosomes occurs?

due to shortening of spindle microtubules and kinetochore movement along spindle fibers

When does telophase begin?

As soon as chromatid movement stops, when they have reached opposite ends of cell

what changes happen at telophase?

-spindle fibers disappear
-chromosomes change to chromatin and are invisible under LM
nuclear envelope forms around new nuclei
-cytokinesis begins

product at the end of telophase?

2 independent daughter cells

What is cytokinesis?

division/cleavage of the cytoplasm

How does cytokinesis occur?

it is achieved by the motor protein Myosin pulling on microfilaments of Actin in the terminal web of the cytoskeleton. this creates a crease called the cleavage furrow around the equator of the cell (fiber ring). 2 daughter cells are similar to mother but smaller

when does cytokinesis happen?

when actin ring contracts. what makes actin contract? myosin.

What is gametogenesis?

production of gametes (sperm and ovum)

what does gametogenesis include?

chromosomal (meiosis) and cytoplasmic

purpose of shape alteration of primary germ cells?

allow them to be ready for fertilization

changes to large round primary male germ cell:

-lose most of their cytoplasm
-develop head, tail and neck (for movement)

other characteristics of sperm cell

-nucleus concentrated in head
-acrosome at head of sperm

function of acrosome

Contains digestive enzymes (lysosomes) so that a sperm can penetrate an egg

why does the body of the sperm contain a lot of mitochondria ?

provide energy

function of microtubules extending from sperm body to end of tail?

allow movement of sperm
energy coming from mitochondria in body

what is the shape of a mature egg/ ovum cell called?

coronaradiata

why is the mature ovum bigger in size than primary female germ cell?

due to increase in amount of its cytoplasm

Other characteristics of a mature ovum?

big, large round nucleus, large nucleolus

function of cells around ovum?

support and nutrition

Where does fertilization occur?

fallopian tubes / uterine tube

When does fertilization take place?

when a sperm cell unites with an egg cell

product of fertilization

diploid zygote = fertilized ovum

what type of division does a zygote go through after fertilization?

mitosis

What controls cell division?

genes called PROTO-ONCOGENES

factors that could induce DNA damage > mutations :

-radiation -chemicals- drugs - xrays- uv light- smoking

Mutations in proto-oncogenes

Become oncogenes that speed rate of cell division in an unorganized manner (nuclear morphology diversity) = TUMORS

common term for malignant tumors:

cancer

difference between benign and malignant tumors

Benign is not cancerous and cannot spread (mole), but malignant is cancer that invades tissue and spreads to other parts of the body (leukemia)

what stops damaged dna from continuously being replicated?

checkpoints or restriction points (R) in G1 and G2 (before and after S)