The Eukaryotic Cell Cycle and Mitosis

Mitosis

* somatic cells divide at the nucleus
* Used for growth and repair
* Create exact copies
* Diploid cells

Meiosis

* create gametes(sex cells)
* different cells
* The result is daughter cells(haploids) which have 1/2 number of chromosomes
* Haploid from each parent forms full chromosomes

What is unique about the eukaryotic cell?

Many more genes than a prokaryotic cell

How are genes in eukaryotic cell grouped?

Grouped in chromosomes

What does each chromosome contain?

* one long dna molecule which has protein molecules(histones) attached to it to increase surface area and volume ratio
* This helps maintain chromosome structure and control activity of its genes
* \*\*\*8 histones+ DNA forms a nucleosome

What does each eukaryotic species have?

* charecteristic number of chromosomes in each cell nucleus

What do chromosomes look like when they are not being divided?

* look like thin loosely packed chromatic fibers

How are chromosomes visible?

* under light microscope
* In process of dividing

What happens before a cell divides?

* chromosomes duplicate to produce sister chromatids(identical DNA) which are joined by the proteins most closely at the __**centromere**__

Kinetachore

Protein complex in sister chromatid

Describe cell division

* Séparation of sister chromatids that are joined through the centromere
* Results in daughter cells(contain complete and identical chromosomes)

What is the cell cycle?

* ordered sequence of events that extends from the time a cel is first formed from a dividing parent cell until its own division

What are the 2 main stages of the cells cycle?

1) Interphase(growing stage)

* cell doubles organelles and replicates DNA

2) Miotic Phase

* actual cell division

What percentage of the cell cycle is spent in interphase?

* 90%

What else is true of the cell when it is in interphase?

Metabolic activity is high

What are the sub phases of interphase?

1) G1

2) S Phase

3) G2 Phase

\*\*\*G0(cells that don’t divide)

Describe the first subphase of interphase

* replication of internal cell components(organelles)
* Cell increases in size

Describe the second subphase of interphase 

* synthesis of DNA through DNA replication(duplicating chromosomes)
* Spans half of the interphase

Describe the third subphase of interphase 

* double checks for everything being done correctly
* Replicates centrioles important for developing spindle fibers

What is the miotic phase?

Interval of the cell cycle when cells physically divide

What are the sub-phases of mitosis?

1) Mitosis

2) Cytokinesis

Describe the first sub-phase of mitosis.

* nucleus and it’s contents divide into 2 daughter nuclei

Describe the second sub-phase of mitosis.

* cytoplasm is divided into two

What is the result of the miotic phase?

* Produces 2 genetically identical daughter cells

How does mitosis distribute the duplicated chromosomes into 2 daughter nuclei?

Through 5 phases

* 1) Prophase
* 2) Prometaphase
* 3)Metaphase
* 4) Anaphase
* 5) Telophase

What happens after the chromosomes are coiled up?

* miotic spindle is made up of microtubules to move the chromosomes to the middle of the cell

Draw a picture of the interphase and label all the parts.

* Draw a picture of the first stage of mitosis
* Label all the parts
* Describe what occurs in it

* Draw a picture of the second stage of mitosis
* Label all the parts
* Describe what occurs in it

* Draw a picture of the third stage of mitosis
* Label all the parts
* Describe what occurs in it

* Draw a picture of the fourth stage of mitosis
* Label all the parts
* Describe what occurs in it

* Draw a picture of the fifth stage of mitosis
* Label all the parts
* Describe what occurs in it

When does cytokinesis occur?

* occurs in animals when a cell constricts and contracts inward to form a cleavage furrow

When does cytokinesis occur in plants?

* occurs when a cell plate(made of cellulose forms)

How does cytokinesis occur in plants?

* since the cells can’t split off due the existence of a non-living cell wall
* During the telophase, membranous vesicles of cell wall material collect at the middle of the parent cell
* The cell plate grows outward to fuse with the cell membrane and he plate’s contents join the cell wall

What are the requirements for cell division?

1) anchorage dependence: cells must attach to the surface

2) density-dependent inhibition: continue dividing until they touch one another

* specific studies suggest that physical contact of cell-surface proteins between adjacent cells are responsible for the inhibition of cell division
* Cancer cells don’t do this

3) animal cells only divide when they are stimulated by growth factors

What are growth factors ?

* a set of proteins that controls the cell cycle

How exactly do growth factors complete their job?

* Signals from the growth factors affect critical checkpoints in the cell cycle determine whether a cell will go through the complete cycle and divide.
* The binding of growth factors to specific receptors on the plasma membrane is usually necessary for cell division.

* How are cancerous cells different from regular body cells?
* Can you give an example?

* They are different because they no longer exhibit regulation
* Ex: VGEF stimulates growth of new blood vessels but overproduction of it can lead to many dangerous cancers

What is the cell cycle control system?

* set of molecules that triggers and coordinates events in the cell cycle

What is a checkpoint in the cell cycle?

* critical control point where stop and go-ahead signals regulate the cycle
* occurs after G1,G2, and Mitosis

What is the default action in most animal cells regarding the cell cycle?

* halt it at checkpoints overridden by specific growth factor proteins

What is cancer?

Disease of the cell cycle

What is a tumor?

* huge masses of cancer cells

What are the 2 types of tumors?

1) Malignant: invade other tissues

2) Benign: abnormal cells remain at their original site

What is metastasis?

* spread of cancer cells beyond their original site

What are some effective cancer treatments?

1) Radiation

2) Chemotherapy

What are oncologists?

* doctors who treat cancers

What is the risk of death by breast cancer?

* 3.3 % mortality rate with a 96.7 % survival rate

What subset of people are more susceptible to breast cancer death?

* people less than 35
* Black people

What do somatic cells contain?

* A specific number of chromosomes


* Humans have 46(23 pairs)

What are homologous chromosomes?

* two chromosomes with 2 different versions of the same gene(alleles) eventually determining someone’s appearance(phenotype)

What are somatic cells?

* Have 2 sets of homologous chromosomes termed diploid

What are gametes?

* haploid cells with a single set of chromosomes

What is a life cycle?

* sequence of stages in the history of an organism, from fertilization to the production of its own offspring

What is a key factor in the life cycle of species that reproduce sexually?

* Having two sets of chromosomes, one inherited from each parent

What do cancer cells start out as?

* start as normal cells, but genetic mutations cause them to lose the ability to regulate their division

What is the heart of the reproduction of cells?

* Cell division is at the heart of the reproduction of cells and organisms because cells originate only from pre-existing cells

What does cell division result in?

* two daughter cells are genetically identical to each other and to the original parent cell
* Before the parent cell splits into two, it duplicates its chromosomes, the structures that contain most of the cell’s genetic information in the form of DNA

What is asexual reproduction?

* Asexual reproduction produces offspring that are all genetic copies of the ONE parent and identical to each other (clones)
* Can be unicellular prokaryotes,eukaryotic yeast, as well as multicellular organisms

What does cell division also allow for?

* 1) Reproduction


* enables sexually reproducing organisms to develop from a single cell into an adult organism(Mitosis)

2) Renewal and Repair: replacing cells that die from normal wear and tear or from accidents(Mitosis)

What does sexual reproduction allow for?

* higher diversity due to the fusion of gametes( sperm+egg=zygote) through meiosis

What is binary fission?

* The process in which prokaryotes reproduce asexually

Where do most prokaryotes carry genes?

* most genes are carried on one circular DNA molecule that, with associated proteins, constitutes the organism’s chromosome

What does the specific process of asexual reproduction include?

Draw a diagram of meiosis.

How is meiosis different from mitosis?

* meiosis means the cell divides twice to form 4 haploid daughter cells instead of once

What occurs in the first division(meiosis I)?

* starts with pairing of homologous chromosomes
* Ends with the separation of homologous pairs into single chromosomes
* produces two daughter cells each with one set of chromosomes

What occurs in the crossing over stage?

* homologous chromosomes exchange corresponding segments after intertwining

What occurs in meiosis II?

* same as mitosis as the sister chromatids are separated but the result is 4 haploid gametes

What are the steps of meiosis?

\

1. Interphase: Chromosomes Duplicate
2. Meiosis I: Homologous Chromosomes Seperate


1. Prophase I
2. Metaphase I
3. Anaphase I
4. Telophase I and Cytokinesis
3. Meiosis II: Sister Chromatids Sepearte


1. Prophase II
2. Metaphase II
3. Anaphase II
4. Telophase II and Cytokinesis

Compare and contrast mitosis and meiosis.

* Similar in origin
* Both mitosis and meiosis begin with diploid parent cells that have chromosomes duplicated during the previous interphase.
* Different in result
* Mitosis produces 2 genetically identical diploid somatic daughter cells; meiosis produces 4 genetically unique haploid gametes.


* Different in purpose
* Mitosis functions for growth and repair within multicellular organisms as well as asexual reproduction for unicellular organisms; meiosis only functions for sexual reproduction

What is locus?

Location of a gene

What is tetradon?

* 4 chromatids

Which chromosomes are not homogoulus?

* 24 is not
* Specifically XY(male)

Describe each meiosis step in further detail.

What is non-disjunction?

A process used to describe abnormal chromosome count

What causes non disjunction?

* failure of a pair of homologous chromosomes to separate during meiosis I or the failure of sister chromatids to separate during meiosis II

What does nondisjunction result in?

* Results in one gamete receiving two of the same type of chromosome and another gamete receiving no copy of that chromosome; two other gametes are not affected

How does a zygote with an abnormal number of chromosomes come come into existence?

* abnormal gamete produced by nondisjunction unites with a normal gamete during fertilization

How does mitosis contribute to the spreading of genetic mistakes?

* Mitosis will then transmit the mistake to all embryonic cells. If the organism survived, it would most likely display a syndrome of disorders caused by the abnormal number of genes

What does nondisjunction look like in meiosis I?

What does nondisjunction look like in meiosis II?

What is a karyotype?

* ordered display of magnified images of an individual’s chromosomes arranged in homologous pairs

What are karyotypes used for and what does it show?

* Shows the chromosomes condensed and doubled, as they appear in metaphase of mitosis
* Used to detect chromosomal abnormalities within haploid or diploid cells

What are loci and why are they helpful?

* stained to reveal band patterns
* helpful in differentiating the chromosomes and in detecting structural abnormalities

How is a karyotype prepared?

lymphocytes are

* isolated
* stimulated to grow
* arrested at metaphase
* photographed under a microscope

What causes Down syndrome?

* trismony 21

What are some Down syndrome symptoms?

* Down syndrome includes
* characteristic facial features(frequently a round face, a skin fold at the inner corner of the eye, a flattened nose bridge, and small, irregular teeth)
* as well as short stature
* heart defects
* susceptibility to respiratory infections
* leukemia
* Alzheimer’s disease

What charecteristic is prominent in people with Down syndrome?

* Almost all males and about half of females with Down syndrome are sexually underdeveloped and sterile

What is the chance someone with Down syndrome passes it on?

* Half the eggs produced by a woman with Down syndrome will have the extra chromosome 21, so there is a 50% chance that she will pass on the syndrome to a child

What are some other similar genetic disorders?

Name the first reason we account for the genetic variation among sexual reproducers?

* Each chromosome of a homologous pair differs at many loci from the other member of the pair

Name the second reason we account for the genetic variation among sexual reproducers.

* Random arrangements of chromosome pairs at metaphase I of meiosis lead to many different combinations of chromosomes in egg and sperm

Name the third reason we account for the genetic variation among sexual reproducers.

* Random fertilization of eggs by sperm greatly increases this variation

Name some other reasons we account for the genetic variation among sexual reproducers.

* During meiosis, individual genes within chromosomes can also be shuffled, providing yet another source of increased genetic variation during sexual reproduction

What is a tetrad?

* pair of homologous chromosomes, where each chromosome contains a pair of sister chromatids, making four copies of each gene

What are homologus chromosomes?

* genes for the same characteristic at corresponding loci

What increases variation even further?

* genetic recombination via crossing over within prophase I

What is crossing over?

* exchange of corresponding segments between non-sister chromatids of homologous chromosomes