cell life cycle- 2 major stages

Cell Life Cycle- 2 major stages• A.

__________• What

happens?• B. _________

What happens?

Interphase – Between Mitotic

phases

• How long (relatively speaking) is this stage?

• What does the DNA look like at this stage?

• What happens at the very end of interphase?

Mitosis

• An highly organized method of replication creating identical daughter cells from one parent cell

• When a cell loses control of mitosis, a CANCER may occur

4 Stages of Mitosis

• Prophase• Metaphase• Anaphase• Telophase

Mitosis Animated

Prophase• EVENTS:• Nuclear membrane breaks

down• Chromatin coils into

chromosomes• Centrioles move apart• Spindle fibres stretch

across the cell

• Chromosomes eventually attach to spindle fibres

Chromatid

ONION ROOT TIP

Metaphase • Spindle fibres pull the chromsomes to line up along the equator of the cell

Anaphase• Chromatids move to opposite poles of the cell

Telophase• The reverse of prophase• cell membrane starts to

pinch• nuclear membrane forms

around each set of chromosomes

• Each has its own nucleus (and the cell is ready to divide)

• Chromosomes at each end of the pole

• Spindles fibres disappear

Cytokinesis• In late

telophase, the rest of the organelles …

great animation of mitosis

Checkpoints in the cell cycle will prevent division if:– If the cell is short of nutrients– If the DNA within the nucleus has not been replicated– If the DNA is damaged

Mutations in genes involving checkpoints can result in an uncontrolled cell cycle. The result of uncontrolled cell division can = cancer.

• Cancer cells have large, abnormal nuclei• Cancer cells are not specialized, so they serve no function• Cancer cells attract blood vessels and grow into tumours.• Cells from tumours can break away to other areas of the body

Compare and Contrast Asexual and Sexual Reproduction

-including the outcomes of mitosis and meiosis

-including methods of asexual and sexual reproduction

Asexual Reproduction• Produces genetically

identical offspring• Requires only one

parent• Is fast and efficient• Does NOT increase

the genetic variation in the species

Sexual Reproduction

• Produces genetically unique offspring (new combinations)

• Requires 2 parents• Increases the genetic

variation of the species

Methods of Asexual

Reproduction

• Binary fission

Regeneration

Fragmentation

Vegetative Reproduction

Grafting

• Insert a scion (twig) of desired plant onto a stock of another

• Scion will continue to grow as the desired plant

Spore Formation

• Bacteria• Microorganisms• Fungi

Budding

• Offspring grows attached to parent

• Falls off when mature

Human Assisted Cloning:

• More complex plants and animals have lost the ability to clone themselves because their cells have become too specialized.

• However, scientists have discovered how to assist the creation of clones in complex organisms.

Human Assisted Cloning – how it’s done:

Scientists can clone complex organisims for two reasons:

1. Reproductive Cloning: To produce a genetically identical organism that because it has desirable characteristics.

2. Therapeutic cloning: To create STEM cells (embryonic) for use in cell therapy. The stem cells can correct health problems, because stem cells can develop into any one of our 200 types of body cells!

• Embryonic Stem cells can develop into ANY kind of cell in our body.

• Therapeutic cloning - to correct health problems–Uses stem cells which can be used to replace

cells damaged from injuries or disease

What can we use use stem cells for?

– Diabetes, spinal injuries, Parkinson’s disease are only a few that can benefit from stem cell therapy

Animation of developent from egg to fetus (includes stem cells)

Why is the use of stem cells considered controversial?

Where else can you get stem cells?

• Some blood stem cells can be recovered from the umbilical cord from newborn children

http://www.blood.ca/CentreApps/Internet/UW_V502_MainEngine.nsf/page/

you_can_be_the_one_match_to_save_a_life?

A new way to get stem cells! (this example is combining

gene therapy with stem

cells!)

The future??

Meiosis

• A highly organized method of producing gametes (haploid)

Cross-overs – mixing up the gene pool

Outcomes of Mitosis and Meiosis• Mitosis Outcomes:

2 identical diploid cells

• Meiosis outcomes: 4 unique haploid gametes

Sexual Reproduction• Fertilization• zygote• Embryo- Fetus (around 8

weeks when major organs have developed)

Factors that may Lead to Mutations.

• A mutation is defined as a change in the DNA nucleotide sequence.

• Changing the nucleotide sequence may change the sequence of amino acids

• Changing the a.a.’s may change the protein (which is supposed to control a specific chemical reaction)

Chemical Factors

• Chemicals (ex. PCB’s) can change the genetic code by reacting with the DNA molecule, changing the chemical make-up of the molecule.

Biological Factors

• Viruses can change the sequence of nucleotides by inserting it’s genes into a sequence

Physical Factors

• Radiation is caused by high energy particles • These particles can literally crash into the DNA

molecule, and cause pieces of the molecule to fall out. The cell will try to repair the damage – sometimes GUESSING what the piece that was missing coded for!

• Other times, the cells simply splices the molecule back together, and hopes it will work out alright

Positive Mutations

• Sometimes, a change in the DNA sequence actually improves the function of an enzyme

• Ex. There are some people that are immune to the HIV virus-

•      that immunity was caused by some type of mutation

Neutral Mutations

• Sometimes, a change in the DNA sequence has no effect – either the amino acid stays the same as it was, or perhaps that part of the enzyme was not critical for it’s function

Negative Mutations• Sometimes, a change in the DNA sequence will

have a negative effect• Either the enzyme won’t get made at all, or it

doesn’t work properly, or it has a negative effect on the animal

• Eg. Hemophilia is caused by a mutation on the X chromosome

Review: Structure of DNA

• A long chain of nucleotides

DNA uncoiled • The sequence of the nucleotides determines the sequence of Amino acids linked together by the ribosomes

The code

• A long chain of amino acids makes a protein.

• The sequence of the amino acids determines the type of protein made

Protein folding

• DNA is a long chain of nucleotides

• Ribosomes “read” the nucleotide chain and construct chains of amino acids based on the nucleotide sequence.

• Chains of amino acids are PROTEINS

So why do our GENES code for PROTEINS?

• Is that all we are? PROTEINS?

Proteins are ENZYMES• Enzymes control ALL the chemical reactions in

the body. • If you know when to make the right enzymes, and

how many to make, you can reconstruct yourself – from scratch

• All your “GENES” are is instructions on how to make specific enzymes.

• Mom gave you your “start-up” package with the first enzymes in it.

• Those enzymes started making more enzymes, and you started developing.