Bio - Exam 3 - Mitosis and Meiosis

In unicellular organisms, division of one cell

reproduces the entire organism

Multicellular organisms depend on cell division for

many reasons (cell turnover)

Cell division is an intergral part of the

cell cycle

cell cycle

the life of a cell from formation to its own division

Genome

all the DNA in a cell 

Prokaryotic genomes are mostly

a single DNA molecule

Eukaryotic genomes are mostly

a number of DNA molecules

DNA molecules in a cell are packaged into

chromosomes

Every eukaryotic species has a characteristic number of 

chromosomes in each cell nucleus

Somatic Cells

nonreproductive cells

two sets of chromosomes

product of mitosis

Gametes

reproductive cells (sperm and eggs)

half as many chromosomes as somatic

product of meiosis

Eukaryotic chromosomes consist of

chromatin

chromatin

a complex of DNA and protein that condenses during cell division

Eukaryotic Cell Division: In preparation for cell division, DNA is

replicated and the chromosomes condense

Eukaryotic Cell Division: Each duplicated chromosome has two

sister chromatids

Eukaryotic Cell Division: sister chromatids

separate during cell division

chromatids are attached at the 

centromere

The cell cycle consists of

mitotic (M) phase

Interphase

Mitotic (M) phase

mitosis and cytokinesis

Interphase

Cell growth and copying of chromosomes in preparation for cell division

about 90 percent of the cell cycle

has 3 subphases

Interphase Subphases

G1, S, G2

Interphase G1 Phase

first gap

growth and energy

Interphase S Phase

Synthesis

DNA replicates

Interphase G2 phase

second gap

Check for mistakes

The cells grows through all three phases of interphase, but chromosomes are only duplicated in 

the S phase

The time it takes a cell to complete the gap phases in interphase

varies dramatically between cell types and between organisms

Mitosis phases

Prophase, Metaphase, Anaphase, Telophasse

Prophase

nucleoli disappear, centrosomes move toward poles

Metaphase

chromosomes line up on metaphase plate

Anaphase

sister chromatids separate to opposite poles of the cell

telophase

nuclear envelope reforms around chromosomes

Chromosome def

a structure composed of a DNA molecule and associated proteins

Chromatin Def

The material that makes up eukaryotic chromosomes; consists of a DNA molecule complexed with histone proteins

Chromatid Def

one strand of a replicated chromosome, with its associated proteins

Sister chromatids

the two strands of a replicated chromosome. when chromosomes are replicated, they consist of two of these. the genetic material in them is identical. when they separate during mitosis, they become independent chromosomes.

Centromere Def

The structure that joins sister chromatids

Kinetochores def

The structures on sister chromatids where microtubules attach

Microtubule organizing center def

any structure that organizes microtubules

Centrosome def

The microtubule organizing center in animals and some plants

Centrioles def

Cylindrical structures that comprise microtubules, located inside animal centrosomes

Mitotic Spindle

an apparatus of microtubules that controls chromosome movement during mitosis

During prophase, assembly of spindle microtubules begins in the

centrosome

Centrosome AKA 

MTOC

After the assembly of microtubules begins in the MTOC, the centrosome replicates, forming

two centrosomes that migrate to opposite ends of the cell, as spindle microtubules grow out of them

The spindle =

centrosomes, the spindle microtubules, and the asters

Aster

what anchors the MTOC to edge of cell

During late prophase, some spindle microtubules

attach to the kinetochores of chromosomes and begins to move the chromosomes

At metaphase, the chromosomes are all lined up at the

metaphase plate

metaphase plate

the midway point between he spindle’s two poles

In anaphase, sister chromatids

separate and move along the kinetochore microtubules toward opposite ends of the cell

(enzymatic cleavage of cohesions)

In anaphase, the microtubules shorten by

depolymerizing tubular at their kinetochore ends (breaking polymers apart)

shorten, don’t pull

During anaphase, nonkinetochore microtubules from opposite poles

overlap and push against each other, elongating the cell

Nonkinetochore microtubules

span entire cell, AKA polar microtubules

in telophase, genetically identical daughter nuclei

form at opposite ends of the cell 

In animal cells, cytokinesis occurs by

a process known as cleavage, forming a cleavage furrow

(actin microfilaments and myosin pinch membrane in two)

In plant cells, cytokinesis occurs by

the formation of a cell plate where the metaphase plate was, new cell walls form

Eukaryotic cell division consists of

mitosis (the division of the nucleus)

Cytokinesis ( the division of the cytoplasm)

Prokaryotes divide through

binary fission

they do not undergo mitosis or meiosis

Cyclin-Dependent Kinase (CDK)

Catalyzes phosphorylation of other proteins to start M-Phase

MPF

M phase promoting factor

Kinases

phosphorylate other proteins which generally makes them active

Cyclin

a regulatory protein, coenzyme

M Phase checkpoints: Pass if

Chromosomes have attached to Spindle apparatus

chromosomes have properly segregated and MPF is absent

G1 Checkpoints: pass if

Cell size is adequate, nutrients are sufficient, social signals are present, DNA is undamaged

G2 checkpoints: pass if

chromosomes have replicated successfully, DNA is undamaged, Activated MPF is present

Cancers

Loss of control of the cell cycle (skipping checkpoints)

Uncontrolled cell growth can lead to

tumors

Benign Tumors

type of cancer that won’t spread/ aren’t life threatening

Malignant Tumors

divide and spread

Malignant tumors can lead to

metastasis

metastasis

the spreading of cancer cells to other parts of the body

Two modes of reproduction

Asexual, sexual

Asexual Reproduction

on parent produces genetically identical offspring, generally through mitosis

Clone

a group of genetically identical individuals from the same parent

Sexual reproduction

two parents give rise to offspring that have unique combinations of genes inherited from the two parents

The Costs of Sexual Reproduction

Energetics of searching for, assessing and mating with another individual

Dangers of doing so (increased risks of predation and disease)

Lower genetic efficiency

Sexual reproduction leads to 

variation, which is required for evolution (survival of the fittest)

Autosomal Chromosomes

non-sex chromosomes

sex chromosomes

chromosomes associated with an individual’s sex

Homologous Chromosomes

chromosomes of the same size and shape with the same genetic material (may have different alleles)

chromosomes cary 

genes, but each gene can be variable

Variants of genes are called

alleles

Meiosis goal is to produce

gametes (haploid, n)

2n

46

n

23

Ploidy

the combination of the number of sets of chromosomes

haploid

organisms only have one copy of each chromosome (n)

diploid

organisms have two copies of each chromosome (2n)

Diploid organisms have 

a maternal chromosome and a paternal chromosome for each pair

Karyotype

number and appearance of the chromosomes

Mitosis creates how many daughter cells

two

Meiosis creates how many daughter cells

four (two cell divisions)

Meiosis reduces the number of chromosome sets from

diploid to haploid

Like mitosis, meiosis is preceded by

the replication of chromosomes

Meiosis takes place in two sets of cell divisions, called

meiosis I and meiosis II

In meiosis, each daughter cell has only

half as many chromosomes as the parent cell

Meiosis I

homologous chromosomes separate, results in two haploid daughter cells with replicated chromosomes

Meiosis I is sometimes called

the reductional division

In Meiosis II

sister chromatids separate, results in four haploid daughter cells with unreplicated chromosomes

Prophase I

typically occupies more than 90 percent of the time required for meiosis

chromosomes condense

Synapsis occurs

synaptonemal complex

Crossing over occurs

each pair of homologues forms a tetrad