The Cell Cycle

CHAPTER 12

VIEW SLIDES> TAKE NOTES TO ORGANIZE AND LEARN THE INFORMATION ALL SLIDES, INFO FROM VIDEOS AND QUESTION TOPICS WILL BE ON EXAM #3

COMPLETE QUESTIONS FOR EACH SECTION. SEND THE COMPLETED QUESTIONS BY MONDAY NOV 7 TO

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The Cell Cycle

blinderl@mccc.edu

READ CHAPTER 12 IN TEXTBOOK

The Key Roles of Cell Division

cell division = reproduction of cellsAll cells come from pre-existing cells

Thought question (do not turn in)What pre-existing cells did your cells come

from?

Unicellular organisms division of 1 cell reproduces organism

Binary fission

ASSIGNMENT: View video on binary fission http://www.youtube.com/watch?v=J6akNYlkehY

QUESTION 1: a.How frequently do some bacteria divide?b.How does this explain their ability to expand their numbers quickly?

Why cells reproduce Development/Growth

Replacement

Repair

Multicellular organisms

Example: embryo adult

Example: stomach lining iscontinually replaced

Example: repair of burn

Watch the videohttp://www.youtube.com/watch?v=f7cXeWxxf

D4

Sea stars can reproduce cells in a way that humans cannot – view and understand.

FYI

Three Hundred Million Cells Die In Your Body Every Minute

It does sounds like a lot but this is actually less than 0.0001% of the amount of cells being replaced in your body every day. (about 10-50 trillion cells are replaced in your body every day)

Cellular Organization of Genetic Material

chromosome = strand of DNA 2 sets of 23 chromosomes in humans = 46

genome = All DNA in a single cell single chromosome (prokaryotes) many chromosomes (eukaryotes)

Assignment: View the data on the website http://morgan.rutgers.edu/morganwebframes/level1/page2/ChromNum.html Explore the number of chromosomes in each type of organism’s cells.

Question 2: a. Is there a correlation between chromosome number and

intelligence? Provide evidence to support your claim.

20 µm

This is an electron micrograph of the46 chromosomes in a human cell.

chromatin complex of DNA and protein

20 µmChromatin normally looksdiffuse - hard to see individual chromosomes

Terms needed to continue

Haploid – a cell with one set of chromosomesDiploid – a cell with two sets of chromosomes

Assignment. Visit the website http://www.ncbi.nlm.nih.gov/books/NBK9863/

Question 3 a. Look carefully at the list – are these diploid, or haploid

chromosome numbers?b. How many chromosomes are in the sperm of a fruit fly?c. Which organisms have genome sizes similar to humans (Mb

size is multiplied by 1 million for total size)

Mitosis – cell division process to replicate cells Ex. Skin cells do this

Meiosis – cell division process to generate unique haploid cells Ex. Spermatogenesis, oogenesis

BE ABLE TO DISTINGUISH BETWEEN MITOSIS AND MEIOSIS

Somatic cells= body cells (2 trillion in adult) two sets of chromosomes (pairs= diploid) Produced by mitosis - 1 diploid cell 2 identical diploid cells

Skin cells produced by mitosis

Gametes sperm and eggs have one set = haploid Produced by meiosis – 1 diploid cell 4 unique cells Occurs only in ovaries, testes

Egg cell (oocyte) is a gamete produced by meiosis

Identical cells Unique cellsDiploid Haploid

Assignment: Read the textbook and study the previous slides to answer the followingQUESTION 4a.A fruit fly sperm contains 4 chromosomes. How many chromosomes . Which of the cells below are diploid? (there are 6)

- fruit fly wing cell - monkey liver cell- haploid cell - plant pollen (contains sperm)- gamete from a fern plant - fish somatic cell- fertilized whale egg- human embryo cell- cell produced by meiosis - cell with 2 sets of chromosomes- sperm of frog - unfertilized bird egg

b. Which of the following terms are associated with mitosis (there are 6)

- sperm - somatic - genetically identical- diploid - ovary - 2n- unique cells - liver cell - 46 chromosomes- 1 set of chromosomes - 4 daughter cells - gametes

Cell Division also includes:

Nuclear division= division of the nucleusCytokinesis = division of cytoplasm

View the video to comparehttp://www.youtube.com/watch?v=rgLJrvoX_qo&NR=1

When both have occurred, there are 2 new cells, each identical to the “parent” cell

The cell cycle = time from new cell to when it divides

Interphase ~ 90% of a cell’s timecell is doing its normal activity during this time

Mitosis - ~ 4o mincell is involved in replicating to make 2 new cells

S(DNA synthesis)

MITOTIC(M) PHASE

G1

G2

A cartoon showing the time cell spends in interphase and mitosis. Note that mitosis is short

Now, we will examine the individual steps in the cell cycle. Give yourself enough time to understand each step before proceeding.

INTERPHASE (~90% of the cell’s time in the cell cycle, not part of mitosis)G1 phase – cell grows, gets readyS phase – DNA replicatesG2 phase – cell grows, gets ready

S(DNA synthesis)

MITOTIC(M) PHASE

G1

G2

Watch the cell cycle videohttp://www.youtube.com/watch?v=O3_PNiLWBjY

Signs of interphase?Note the distinct nuclear membraneNote that the chromosomes inside the nucleus

are not visible (they are too thread-like at this stage to see)

Cell membrane

Photo of a fish cell

S phase of InterphaseChromosomes replicate to

form:

Sister chromatids = 2 for each chromosome, they are attached at the centromere (constricted region)

This is one chromosome that has replicated into a pair of sister chromatids

All 46 chromosomes in a human cell have been replicated to form sister chromatids held together at the centromeres

Assignment: review the textbook and notesQuestion 5a)Number of chromosomes in a human sperm or egg cellb)Number of chromosomes in a human fertilized eggc)Total number of sister chromatids in a human cell after S phase of Interphase (not sister chromatid pairs, individual sister chromatids)

Prophase Metaphase Anaphase Telophase

Cytokinesis (division of cytoplasm) by late telophase

PHASES OF MITOSIS

A. Chromosomes condense = they become thicker and shorterB. Nuclear membrane breaks apartC. Mitotic spindle forms from centrioles

I. Prophase of Mitosis

WATCH THE PROPHASE VIDEOhttp://www.youtube.com/watch?v=BFDSlHv3SZU

A chromosome in prophase= 2 identical sister chromatids held together at centromere

Note the absence of a nuclear membrane in the cell that has entered prophase

The nuclear membrane is breaking up

A fish cell

Prophase of mitosisThis is a slide of onion cells with chromosomes stained red

View: condensed chromosomes in prophase and absence of nuclear membrane

Cannot see the mitotic spindle in this photo

The mitotic spindle in prophase

Remember the centriolesThey have replicated and

moved to opposite sides (poles) of the cell

AND, microtubules have grown from them – the red lines – they attach to the centromeres of the sister chromatid pairs

The microtubles are called spindle fibers

http://www.nature.com/scitable/definition/spindle-fibers-304

Scitable is a website that contains information on many aspects of biology and genetics. The components of the mitotic spindle are covered here.

You may need to register, its free. If you do not have a textbook, the definitions on Scitable will be useful to you.

Assignment: Read the text and study the slides. Question 6a.Are the two sister chromatids that compose a chromosome in prophase identical?b.To what structure do the mitotic spindle microtubules attach on the chromosomes?c.What are the components of the mitotic spindle?d.What are centrioles composed of?e.What is meant by “chromosomes condense” ?

WATCH THE PROPHASE VIDEOhttp://www.youtube.com/watch?v=BFDSlHv3SZU

II. Metaphase of mitosis

chromosomes (still in sister chromatid pairs) line up at the metaphase plate

midway between spindle’s two poles

Centrioles with spindle fibers

Chromosomes are lined up

Fish cell

The chromosomes here do not look as neat – but their centromeres are in a line on the metaphase plate

Metaphase plate

Centriole with spindle fibers

Assignment: Watch the metaphase video

http://www.youtube.com/watch?v=8C7Y1F1uyQs&feature=related

Question 7a.How can you determine visually that a cell is in metaphase?b. About how long in minutes or hours is metaphase?c.Is the spindle apparatus (mitotic spindle) obvious during metaphase?d.Are the sister chromatids still attached at the centromere during metaphase?

III. Anaphase sister chromatids separate ! They split into

individual chromosomes.Mitotic spindle shortens –to move newly

separated chromosomes toward opposite ends of cell

This is tightly controlled – need a full set of chromosomes moving to each side!

Plant cell chromosomes in red

Fish cell – note that a set of chromosomes, is moving to each end of the cell. The cell also is huge

Assignment: Watch the anaphase videohttp://www.youtube.com/watch?v=k3ECNH1MSCw&feature=related

Question 8a. Once sister chromatids have split, what are they referred to as?b. About how long does anaphase of mitosis take?c. Does each side of the cell have a full set of chromosomes at the end of anaphase?d. What happens to the mitotic spindle?

IV. Telophase of mitosis

Identical nuclear membranes form around each set of chromosomes

Chromosomes start to decondense

CytokinesisDivision of cytoplasmanimal cells

cleavage furrow

plant cells cell plate

Cleavage furrow100 µm

Daughter cells

(a) Cleavage of an animal cell (SEM)

Contractile ring ofmicrofilaments

Cleavage furrow in dividing cell

Daughter cells

(b) Cell plate formation in a plant cell (TEM)

Vesiclesformingcell plate

Wall ofparent cell

New cell wallCell plate

1 µm

Cell plate in plant cell

Assignment: Read textbook and study slides

Question 9 a.Identify the phase in A – D of this photo b.List one feature that tells you the cell in in that particular phase of mitosis CA

B D

Nucleus

Prophase1

NucleolusChromatincondensing

A plant cell in interphase

Prometaphase2

Chromosomes

prophase

Metaphase3

metaphase

Anaphase4

anaphase

Telophase5

Cell plate 10 µmTelophase and cytokinesis with cell plate

Cell plate

Onion cells in various stages of the cell cycle

Assignment – read textbook and study slidesQuestion 10 Fill in the appropriate phase of mitosis or interphase:

a. DNA synthesis occurs : ____b. Interphase consists of subphases: ____ ____ ____c. Sister chromatids form : ____d. Stage that involves a cleavage furrow ____e. Beginning of cell cycle ____f. Sister chromatids separate ____g. The nuclear membrane is visible ____h. Chromosomes condense ____i. Centromeres line up ____j. 1 cell divides into two cells ____k. A distinct nuclear membrane is visible ____VIDEOS TO ASSIST YOU next page

http://www.sumanasinc.com/webcontent/animations/content/mitosis.html sumanas

http://www.youtube.com/watch?v=3kpR5RSJ7SA&feature=related ms stokes bio

http://www.youtube.com/watch?v=AhgRhXl7w_gpisgahscience

http://www.johnkyrk.com/mitosis.html Kyrk

Evolution of Mitosismitosis is thought to have evolved from binary

fission

Some protists exhibit cell division intermediate between binary fission and mitosis

The next 2 slides are from the textbook and are summary slides of Interphase G1, S, G2 and M (mitosis)

Prophase PrometaphaseG2 of Interphase

PrometaphaseProphaseG2 of InterphaseNonkinetochore

microtubulesFragmentsof nuclearenvelope

Aster CentromereEarly mitoticspindle

Chromatin(duplicated)

Centrosomes(with centriolepairs)

Nucleolus Nuclearenvelope

Plasmamembrane

Chromosome, consistingof two sister chromatids

Kinetochore Kinetochoremicrotubule

Metaphase Anaphase Telophase and Cytokinesis

Metaphase Anaphase Telophase and Cytokinesis

Cleavagefurrow

Nucleolusforming

Metaphaseplate

Centrosome atone spindle pole

SpindleDaughterchromosomes

Nuclearenvelopeforming

The cell cycle is regulated by molecular controls

Short cell cycle– ex. skin cell divides frequently

Longer cycle– ex. brain cellMitosis always takes about 40 minutes so the

cell cycle differences are in interphase

Cycle completed in 24 hours or years in brain cellin skin cell

tightly coordinatedcheckpoints - cell cycle will not proceed until it

checks itself out!Why does the cell need checkpoints?

Has DNA been copied correctly? if there are mutations, they need to be fixed or cell must die!.

Are chromosomes moving correctly? during anaphase, a full set of chromosomes must move to the

new cells How is the mitotic spindle?

If its not attaching correctly to chromosomes, they wont move correctly

Is the cell big enough? it may need more organelles, membranes etc.

Cell cycle control

SG1

M checkpoint

G2M

Controlsystem

G1 checkpoint

G2 checkpoint

The red pieces represent times that the cell meets a checkpoint

The G1 and G2 checkpoints are in interphase

G1 checkpoint (interphase) most important If no “go” signal, cell will move to an

opt out phase called G0 phase (non-dividing) Most cells are in G0

Can re-enter cell cycle

These healthy brain cells are in Go – they have opted out of the cell cycle, and can stay like this for years

This is a slide of heart muscle tissue. The cells are in Go – they are functioning normally, just not dividing

This is where most cells are, in Go – not dividing, but working normally

Back to dividing cells and the G1 checkpoint

G1

G0

(a) Cell receives a go-ahead signal

G1

(b) Cell does not receive a go-ahead signal

G1

G0

G1 checkpoint

(a) Cell receives a go-ahead signal

G1

(b) Cell does not receive a go-ahead signal

The G1 checkpoint – what does it do for the cell?

Ensure that enough nutrients are available to support new cells

Lets the cell continue in the cell cycle If the G1 checkpoint is not passed, the cell

exits the cell cycle and switches to non-dividing G0 state

Assignment: View the video http://www.youtube.com/watch?v=O3_PNiLWBjYQUESTION 11a. The restriction point mentioned is the G1 checkpoint. What does the cell do if it does not pass the G1 checkpoint?b. If the cell passes the G1 checkpoint – what does it commit itself to doing?c. What is the next cell cycle phase after G2 of interphase?

The G2 checkpointensures that DNA replication in S phase has

been completed successfully. 

The M checkpointensures that all chromosomes are attached to

the mitotic spindle.

Last assignment: View the video http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__control_of_the_cell_cycle.html

QUESTION 12. Fill in the cell cycle stage or cell cycle checkpoint

a. List the 4 main phases of the cell cycle (do not include the C phase)

b. What is the name of the phase in which cells that do not pass the G1 checkpoint enter?

c. If the G1 checkpoint is passed, what then happens to the DNA chromosomes in the cell?

d. If a cell does not pass the G2 phase, it often self destructs – in what way do you think this is protective for the organism?

e. What are the 4 sub-phases of mitosis?f. Once two new daughter cells are produced (after cytokinesis),

which phase of the cell cycle do they each enter?

Format for question submission 1

a. b.

2 a. b.

3 a. b.

4 a. b. c. d.

Follow this pattern for questions 1 – 12. Full sentences only when necessary.

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SUBMIT ANSWERS TO QUESTIONS 1 –12 in an email to blinderl@mccc.edu by 11:59 pm Monday Nov 7th.

You will receive a response that your email has been received