Chromosomes, The Cell Cycle and Mitosis

Cells

Chromosomes

Genes

DNAOrganism

Nucleus

Chromosome

A structure that forms when DNA wraps around proteins and coils up.

Chromosomes only form right before the cell is going to divide.

Each half of a chromosome is called a chromatid. Sister chromatids are

identical to each other. Chromatids are joined at a

centromere. Gene: Segment of DNA

found on a chromosome. Each gene codes for a

specific traits. Each chromosome has

many genes on it.

Chromosome Structure

Two Types of Chromosomes Autosomes- chromosomes that do not

help determine the gender of the individual (most of the chromosomes in your body)

Sex Chromosomes- in humans, they are X and Y; they determine the gender of the individualXX = FemaleXY = Male

Two types of Cells

Gametes- the reproductive cells (sperm for males, eggs for females).

Somatic Cells- all of the cells in the body that are not gametes.Ex – skin cells, muscle cells, brain cells

Chromosome Number in Cells

Different cells can have different numbers of chromosomes depending on where in the body they are located.

Diploid VS HaploidDiploid (2N)– two sets of chromosomes

(one from mom, one from dad) • Somatic cells are diploid

Haploid (N or 1N)– one set of chromosomes

• Gamete cells are haploid

Different organisms have different #’s of chromosomes.Ex: Drosophila melanogaster (fruit flies) : 8 Homo Sapiens (human): 46 Podocnemis uuiilis (turtle): 28

Karyotype - A karyotype is a picture of all of the chromosomes in the cell of an individual, taken right before the cell divides.

Humans: 22 Pairs of Autosomes, 1 Pair of Sex Chromosomes

Homologous Chromosomes

Disorder Activity with Questions

What notation would you use to characterize each disorder?

Is this disorder an autosomal or sex chromosome disorder?

How many chromosomes does a person have with each disorder?

MUTATIONS

Point Mutations (occur in the DNA on the genes)

A. Addition – adding on of extra genes• A B C D A B B C D

B. Deletion – substraction of genes• A B C D A C D

C. Substitution – a different is gene is put in place• A B C D A B F D

D. Translocation – genes are switched around• A B C D C D A B

Chromosomal Mutations (occur in the genes on the chromosome)

MUTATIONS

Some genetic disorders are characterized by having too many or too few chromosomes.

Trisomy 21 Also known as “Down’s Syndrome”

Characterized as having an extra chromosome on the 21st pair.

Affects approximately 800 in 1,000

births

Maternal Age Risk at birth 15 to 24 years 1 out of 1300 25 to 29 years 1 out of 1100 35 years 1 out of 350 40 years 1 out of 100 45 (and older) 1 out of 25

Klinefelter’s Syndrome Characterized as a male with an extra “X” chromosome (XXY) The condition exists in roughly 1 out of every 500 to 1,000 males Extra “X” causes slight feminization

(including small penis, tall physique, enlarged breast tissue and

infertility)

Turner Syndrome Characterized as a female with only one “X” chromosome (XO) Turner syndrome occurs in about 1 out of 2,000 live births Symptoms include webbed neck, drooping eyelids, short height

and infertility

THE CELL CYCLE

All somatic cells undergo the cell cycle in order to prepare for cell division (mitosis)

Mitosis is a form of asexual reproduction. The cells that form as a result of mitosis are clones (identical copies) of the original cell.

Why do our cells need to divide????

1. Growth of the organism

2. Repair of cells or replacement of “dead” cells

Stages of the Cell Cycle

G1 PhaseS PhaseG2 PhaseMitosisCytokinesis

G1 (growth 1) Phase

First growth stage Cell increases in size

Synthesis (S) Phase

Copying of all DNADNA is replicated

Chromosomes duplicatedChromosomes needs to be copied before a cell divides, so that each new cell has the correct amount of DNA and the correct number of chromosomes.

G2 (growth) Phase

Cell continues growing.

Interphase – Resting Stage

Interphase is the first 3 phases of the cell cycle togetherG1, S and G2

Cells carrying on normal activities Chromosomes aren’t visible (not coiled

up). Normal cell metabolism and processes

are occurring. Occurs before mitosis. Includes phases of

cell cycle “getting ready” for mitosis

Interphase

Mitosis (M) and Cytokinesis Phases

Cell growth & protein production have stopped.

The cells energy is used to make 2 daughter cells (splitting of original cell into 2). Mitosis – division of the nucleus into 2

nuclei in one cell. Cytokinesis – division of cytoplasm,

resulting in 2 new cells.

Cell Cycle CheckpointsThe cell has checkpoints to ensure that each phase was completed correctly.

G1: is the cell big enough

S/G2: did the DNA copied correctly

Mitosis (and Cytokinesis): making sure the cell divided correctly.

Checkpoints not working and the cell dividing uncontrollably can lead to cancer.

Give each student has a copy of the “Understanding Cancer” worksheet from the NIH: Cell Biology and Cancer curriculum guide. This is available online at: http://science.education.nih.gov/supplements/nih1/cancer/guide/pdfs/ACT2M.PDF (To see the entire Cell Biology and Cancer curriculum guide, go to http://science.education.nih.gov/supplements/nih1/cancer/default.htm) Use a computer and projector to show students the 5 animations available online at: http://science.education.nih.gov/supplements/nih1/cancer/activities/activity2_animations.htm

SURVEY

IPAD: Internet CODE: S2013109

GOOGLE: Endicott research center

CANCER

The disease caused by an uncontrolled division of abnormal cells in a part of the body.

A malignant growth or tumor resulting from such a division of cells.

Stages of Mitosis

ProphaseMetaphaseAnaphaseTelophase

PROPHASE DNA coils tightly & becomes

visible as chromosomes. Nuclear membrane

disappears Centrioles migrate to poles

Centrioles: organelles that produce spindle

Spindle fibers begins to form

Prophase -under the microscope

METAPHASE

Spindle fibers from centrioles attach to each chromosome.

Chromosomes line up in the middle of the cell.

Metaphase –under the microscope

ANAPHASE

Chromosomes are already separated into sister chromatids at the centromere.

o Spindle fibers shorten and each chromatid is pulled to the opposite end of cell.

Anaphase –under the microscope

TELOPHASE Separation of chromosomes into

chromatids is completed Nuclear membrane reforms.

Now have two nuclei in one cell Chromosomes uncoil

Telophase – under the microscope

       Plant             Animal

CYTOKINESIS Cytoplasm division Occurs after chromosomes separate

and two nuclear envelopes reappear. Forms two, identical daughter cells

(they are identical to the original cell)

Check your chromosome numbers!!!

Human Cell:

Before G1 –

46 chromatids

After S –

92 chromatids (46 chromosome pairs)

After mitosis –

2 cells each with 46 chromatids!!

Daughter cells are identical to the parent cell!!!