Mitosis

Why do cells need to divide?

Recap… Cell theory…

Cells are the basic structural unit of life Cells are the functional units of life Cells come from pre-existing cells

Overview Why do cells need to divide?

Repair, growth, development Types of reproduction

Sexual Genetically different 2 parents Takes time to develop, better chance of survival

asexual Genetically identical One parent Many offspring very quickly

DNA Blueprint of life, nucleic acid Chromatin

Granular genetic material, spread out in nucleus of non-dividing cells

Chromosomes Condensed genetic material, in dividing cells

Sister chromatids Identical copies of Chromosomes joined by

a centromere (“centro-” middle)

Humans 46 chromosomes

46 sister chromatids One from your mom, one from your dad

Cell Cycle: Life of a Cell

Cell Cycle Interphase

90 % of cell’s life, non dividing G1 phase

Grows, makes organelles S phase

DNA Synthesis…DNA replicates G2 phase

Cell prepares to divide, makes sure it has all important organelles for division

M phase When the cytoplasm and nucleus of the cell

divides

Cell Cycle There are check points in G1, S, and G2

Make sure cell is ready to move onto the next phase (has all necessary organelles, copied DNA, etc.)

Once the cell has past the G1 checkpoint, it will complete the cell cycle

Some cells stay in the G1 phase all their life (muscle cell, brain cells)

Regulators of Cell Cycle Cyclins

Protein that regulates the timing of the cell cycle in eukaryotic cells

Levels of cyclins rise and fall throughout the cell cycle

Cyclin-dependent Kinases (cdks) Enzymes that are activated when they bind

with cyclin and they make the cell cycle continue

Regulators Internal

Factors within the cell that control cell cycle Cyclin and CDKs

Allow cell cycle to proceed only when certain processes have occurred

Replication of chromosomes Chromosome Attachment to spindle before anaphase

External Factors Outside the cell

Growth factorsmolecules that bind to cell surface that signal cell to divide

Similar cells have molecules that have opposite effect so that when it becomes to crowded, cells stop dividing

M-phase Consists of mitosis and

cytokinesis Mitosis

Process by which the nucleus of a cell divides

One parent cell makes two identical daughter cells

This is how organisms repair tissue and grow and develop

Cytokinesis-division of the cytoplasm

Depending on cell type… Mitosis can take a few minutes or a few

days Muscle cells (non-dividing) Nerve cells (non-dividing) Skin cells (divide all the time) Digestive Tract cells (divide all the time)

Life Span of Some Human Cells

Cell type Life span Cell divisionLining of esophagus 2-3 days Can divide

Lining of small intestine 1-2 days Can divide

Lining of the large intestine

6 days Can divide

Red blood cells Less than 120 days Cannot divide

White blood cells 10 hours to decades Many do not divide

Smooth muscle Long-lived Can divide

Cardiac (heart) muscle Long-lived Cannot divide

Skeletal muscle Long-lived Cannot divide

Neurons (nerve) cells Long-lived Most do not divide

Prophase 50-60% of time Chromosomes become visible Centrioles develop in cytoplasm near nuclear

envelope Centrioles separate and migrate to opposite ends

of nuc. Env. Centrosome

Region where Centrioles are found Organize the “spindle”

Fan like microtubule structure that helps separate chromosomes

Plants do NOT have Centrioles

End of prophase Chromosomes coil together tightly Nucleolus disappears Nuclear envelope breaks down

Metaphase Few minutes Chromosomes line up in middle (M in

metaphase MIDDLE) Microtubules connect centromere of each

chromosome to the 2 poles of spindle

Anaphase Centromeres joining sister chromatids

separate and become individual chromosomes

They are dragged by fibers to opposite poles

Ends when chromosomes stop moving

Telophase Opposite of prophase Condensed chromosomes disperse into

tangle of material Nuclear envelope reforms Spindle breaks apart Nucleolus becomes visible At the end 2 identical nuclei in one cell

Cytokinesis Happens at the same time as Telophase Division of cytoplasm Animal Cells

Cell membrane drawn inward until it pinches off and forms 2 id daughter cells

Plant Cells Cell plate forms between nuclei Cell Plate develops into separate membrane Cell wall appears

Regulators of Cell Cycle Cyclins

Protein that regulates the timing of the cell cycle in eukaryotic cells

Levels of cyclins rise and fall throughout the cell cycle

Cyclin-dependent Kinases (cdks) Enzymes that are activated when they bind

with cyclin and they make the cell cycle continue

Regulators Internal

Factors within the cell that control cell cycle Cyclin and CDKs

Allow cell cycle to proceed only when certain processes have occurred

Replication of chromosomes Chromosome Attachment to spindle before anaphase

External Factors Outside the cell

Growth factorsmolecules that bind to cell surface that signal cell to divide

Similar cells have molecules that have opposite effect so that when it becomes to crowded, cells stop dividing

MEIOSIS

Gregor Mendel

1822 Austrian monk University of

Vienna In charge of

the Garden

What Gregor Mendel Knew…

Each organism must inherit a single copy of every gene from each of its “parents”

Each of the organisms gametes must contain just one set genes When gametes are formed, there must be a

process that separates the 2 sets of genes so each gamete gets one set

Karyotype A photograph of a organism’s

chromosomes, arranged according to size

http://upload.wikimedia.org/wikipedia/commons/5/53/NHGRI_human_male_karyotype.png

http://en.wikipedia.org/wiki/File:Down_Syndrome_Karyotype.png

Chromosome Number Homologous chromosomes

Chromosome that has a corresponding chromosome from the opposite-sex parent

Fruit fly has 8 chromosomes 4 from mom 4 from dad

Diploid Di= two sets Cell that contains both sets of homologus

chromosomes Cell contains

2 complete sets of chromosome 2 complete sets of genes

Number of chrms in diploid cell represented by 2N

For Drosophilia (fruit fly) 2N=8 Mendel said:

Each adult cell contains two copies of each gene

Haploid Means “one set” Refers to cells that contain only one set

of chromosomes Gametes (sex cells) Represented by N Drosophilia fruit fly

N=4

How are haploid (N) gametes made from diploid (2N) cells?

Meiosis Process of reduction division in which the

number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell

Meiosis 2 distinct stages Meiosis I

A diploid cell enters here Meiosis II

At the end of this, the diploid cell that entered meiosis has become 4 haploid cells

Meiosis I Before meiosis 1, each chromosome is

replicate Then they divide like in mitosis What happened in mitosis?

PMAT Tetrad

STRUCTURE MADE WHEN EACH CHROMOSOME PAIRS UP WITH ITS HOMOLOGOUS CHROMOSOME

4 CHROMATIDS IN A TETRAD

Prophase 1 Each chromosome pairs with its

homologous chromosome making a tetrad

As they pair up in tetrads, chromosomes exchange portions of their chromatids in the process …. CROSSING OVER

Crossing Over

Metaphase1 Spindle fibers attach to chromosomes

Anaphase 1• The spindles pull homologous

chromosomes apart to opposite poles/ends

Telophase 1• Nuclear membranes form and cell

separates into two new cells

Now what do we have? 2 new daughter cells Are they identical to the parents?

No The parent has 4 chromosomes Each daughter cell has 4 chromosomes but they

are different because of crossing-over Each daughter cell has a set of chromosomes

and alleles different from each other and different from the parent diploid cell

Meiosis II Unlike Mitosis, Neither cell goes through

a round of chromosome replication Each cell’s chromosome has 2

chromatids

Prophase II Meiosis I resulted in 2 “seemingly” diploid

cells Remember they are genetically different b/c

of crossing over in prophase I We still need to cut this number in half to

reach our goal of 4 haploid cells

Metaphase 2 Chromosomes line up in middleAnaphase 2

• Sister chromatids separate and move to opposite poles

Telophase 2• Meiosis II results in 4 haploid (N)

daughter cells• 4 daughter cells contain haploid number

of chromosomes, just 2 each

Gamete Formation

Male Haploid gametes produced by meiosis are called

sperm Female

Haploid gamete produced by meiosis is called an egg

Cell divisions at the end of meiosis one and two are uneven so one cell gets most of the cytoplasm (the EGG) and the other three are called polar bodies (don’t participate in reproduction)

Mitosis vs. Meiosis Mitosis

Results in the production of two genetically identical DIPLOID cells

Daughter cells have sets of chromosomes identical to each other and to parent cell

MITOSIS allows body to grow and replace other cells

Asexual reproduction Meiosis

Results in four genetically different HAPLOID cells MEIOSIS is how sexually reproducing organisms

make gametes

Genes

Microscope Lab Analysis Mitosis/Meiosis

Microscope Lab Lab notebooks Title “Cell

Division Microscope Lab”

MUST sketch each stage and label the power

Label slide name Stage of mitosis or meiosis Power of the objective

used to observe cell Need to observe each

stage of mitosis and meiosis