Role of DNA

1. Info. In DNA must be present in each cell after division

2. Stores info for which proteins to make and when

3. Directs cell activities 4. DNA gets copied and

redistributed during division

Role of DNA

A single chromosome contains thousands of genes that code for proteins involved in determining how a person’s body develops and function

Pro vs. Eu

How many chromosomes do we have?

1. What is the main difference between Prokaryotic and Eukaryotic organisms?

2. How does cell reproduction occur in prokaryotic organisms?

3. Where does cell reproduction occur in

eukaryotic organisms?

Chromo-somes

1. Each human somatic (body) cell has 23 pairs of chromosomes ( = 46 total chromosomes)

Chromosomes differ in size, shape

Contain thousands of genes that determine how the body functions and develops

Chromo-somes

2. Homologous chromosomes- Each 23 pairs of chromosomes consists of 2 homologues

Similar in size, shape and genetic content (chromatids that are connected)

Chromo-somes

3. One half of each chromosome pair comes from the mother and the other half from the father

Chromo-somes

A somatic cell, that contains 2 sets of chromosomes is diploid

Gametes (sex cells) only have 1 set of chromosomes - haploid

Zygote - a fertilized egg cell We use the symbol “n” to

represent one set of chromosomes

Chromosome numbers in common species

Haploid and Diploid Chromosome Numbers

Autosomes 22 of the chromosome pairs in humans are called autosomes - not directly involved in determining the gender of an individual

Sex Chromosomes

One of the chromosome pairs containing genes that determine the sex of the individual• X and Y• XX - female• XY- male

• The sex is determined by the male

Changes in chromo-some number

1. Presence of all 46 chromosomes is essential for normal development and function

2. Humans missing one chromosome typically do not survive

Changes in chromo-some number

Can detect this in Karyotype

3. More than two copies of a chromosome - trisomy (improper development occurs)

Ex: Down Syndrome (21)

Non-disjunction

When chromosomes don’t separate properly when egg and sperm form

One gamete ends up with both chromosomes, the other has none

Trisomy results when abnormal gamete fuses with another

How many chromosomes do humans have? How many pairs?

What is the difference between “haploid” and “diploid”?

Give the sex chromosomes for females & males

Why is it essential to have all 46 chromosomes?

Draw a pair of homologues, draw a gene on one of the homologues, and label the chromatids

Change in chromo-some structure

MUTATION - change in chromosome structure (4 TYPES)

Change in chromo-some structure

1. Deletion- piece of chromosome completely breaks off (often fatal)

Change in chromo-some structure

2. Duplication- chromosome fragment attaches to its homologue (doubles the info - 2 copies of a gene)

Change in chromo-some structure

3. Inversion- chromosome piece reattaches to original chromosome in reverse orientation

Change in chromosome structure

4. Translocation- chromosome piece attaches to non-homologous chromosome

All of the four mutations discussed could prove fatal for

the individual

Cell Cycle Repeating sequence of growth and division in the life of an organism

Cell Cycle A cell spends 90% of its time in the first three phases – called Interphase• G1• S• G2

Cell Cycle G1- First Growth Phase• Rapid cell growth and

development, routine functions• Major part of cell life spent here• Non-dividing cells remain here• Muscle cells and nerve cells

always here, cannot be replaced

Cell Cycle S- Synthesis phase• DNA copied, end up with sister

chromatid

Cell Cycle G2- Second Growth Phase• Cell prepares nucleus to divide• Microtubules assembled for

moving chromosomes during mitosis

Cell Cycle Mitosis- nucleus divides into two• Each nucleus ends up with

same type and number of chromosomes

• Allows organisms to: Grow Replace damaged tissue Asexually reproduce

Cell Cycle Cytokinesis- cytoplasm divides in half

Control of the cell cycle

1. Cell growth checkpoint (G1) decides whether the cell will divide• A. Cell must be healthy and

large enough first• B. Proteins will stimulate

transition to S phase

Control of the cell cycle

1. Cell growth checkpoint (G1) decides whether the cell will divide• C. If conditions are unfavorable

or cells need a rest, growth will stop here

• D. Nerve and muscle cells remain here forever

Control of the cell cycle

2. DNA synthesis G2 checkpoint- DNA repair enzymes check the DNA replication• A. Once past this point,

proteins trigger mitosis

Control of the cell cycle

3. Mitosis checkpoint- triggers end of mitosis• Signals beginning or G1 phase

again

Losing Control of the cell cycle

Cancer- uncontrolled growth of cells caused by:• A. Mutagens- readily damage DNA

(pollutants, radiation, other environmental factors)

• B. When gene coding for proteins that regulate cell cycle are mutated

Losing Control of the cell cycle

Cancer- uncontrolled growth of cells caused by:• C. When growth promoting

proteins are mutated and actually speed up the rate of cancer Oncogenes- accelerate rate of cell

division

Losing Control of the cell cycle

Cancer- uncontrolled growth of cells caused by:• D. When mutations inactivate the

control proteins that normally slow/stop cell cycle Tumor Suppressor Genes- releases the

“brakes” on cell division

Differentiate between the G1, G2 and S phases of the eukaryotic cell cycle

Relate what occurs at each of the three principal checkpoints in the cell cycle

Why are individual chromosomes more difficult to see during interphase than during mitosis?

Mitosis: Spindles

Made of centrioles and microtubule fibers that move chromosomes during cell division• A. Extra set made right before

division• B. Travel to opposite ends of cell• C. Only animal cells have centrioles• D. Animals and plant cells both have

spindle fibers

Mitosis: Spindles

E. Microtubules attach to cell poles and chromosome centromeres

F. Chromosomes begin to move towards opposite ends of cell

G. Spindle fibers reel in the attached chromosomes as the ends of the fibers at the poles are broken down

H. Each pole gets a full set of chromosomes

46 X’s 92 X’s 46 X’s

46 X’s

46 X’s

46 X’s

Fertilized Cell

Chromosomes copied

Mitosis: Stages

1. PROPHASE• Chromosomes uncoil, become visible• Nuclear envelope disappears• Spindle forms

Mitosis: Stages

2. METAPHASE• Chromosomes move to center of cell

and attach to spindle fibers along equator

Mitosis: Stages

3. ANAPHASE• Centromeres divide• Sister chromatids split and move to

opposite poles as spindle fibers shorten

Mitosis: Stages

4. TELOPHASE• Nuclear envelope reforms• Chromosomes recoil• Spindle and fibers break down

Mitosis: Stages

5. CYTOKINESIS• Cytoplasm divided in half, cell

membrane reforms• Animal: cell pinches in half by belt of

protein• Plant: vesicles from golgi line down

middle of cell to make a cell plate New cell wall grows on either side of

plate Plate breaks cell into two

Mitosis: An Interactive Animation

Molecular Expressions Cell Biology: Mitosis Interactive Java Tutorial

Home(page) Movies - QT and Flash to illustrat...

Dr Chromo's school: mitosis Molecular Expressions Photo Gallery:

Mitosis Mitosis The Cell Cycle & Mitosis Tutorial Mitosis: An Interactive Animation

Describe the function of the microtubules during anaphase

Describe the events that occur during each of the four stages of mitosis

Compare how cytokinesis occurs in plant cells and how it occurs in animal cells