The Cell Cycle & CancerHonors Bio

Human DNA Math for fun! A single molecule of DNA has 1,000’s of

genes!

A single strand of DNA ~5cm long

Each somatic cell has 46 molecules of DNA› 5cm x 46 = 230 cm of DNA per cell!

You have about 100 trillion cells› 230 cm x 100,000,000,000,000 = 23,000,000,000,000,000 cm of DNA in you body!!!!

How does it all fit?

SUPERCOILING!!

http://www.dnalc.org/resources/3d/07-how-dna-is-packaged-basic.html

Be sure to discuss each answer with your group!Complete Mitosis POGIL

Chromosome packaging• Eukaryotic chromosome – 1

d/s DNA molecule w/associated proteins

• Each chromosome and its copy stay attached as sister chromatids and are attached by a kinetochore (protein) at the centromere (narrowing)

• DNA winds twice around proteins called histones and is collectively referred to as a nucleosome

• Why?• Prevents tangling• Regulates gene expression

Chromosomes• Most prokaryotic cells have 1 long circular chromosome• Number of chromosomes in the nucleus of eukaryotic

cells varies by species

• Genome – entire collection of genetic information within the cell

• Multicellular organisms have 2 types of cells:• Somatic cells – all body cells• 2 sets of chromosomes (1 from each parent)

• Gametes – reproductive cells (sperm & egg)• 1 set of chromosomes

Homework:

• Find an article about the human genome project• Underline and define unfamiliar terms

• Write a paragraph summary using the guidelines provided

Karyotype• Human Chromosome number

• Somatic cells= Diploid (2n) 46• Gametes = Haploid (n) 23

• Humans 23 pairs of homologous chromosomes

• Autosomes 1-22• Sex chromosomes 23

XX- femaleXY- male

Preparation:1. Using cells in tissue culture2. Pretreating cells in a hypotonic solution,

which swells them and spreads the chromosomes

3. Arresting mitosis in metaphase by a solution of colchicine

4. Squashing the preparation on the slide forcing the chromosomes into a single plane

5. Cutting up a photomicrograph and arranging the result into an indisputable karyogram.

Assignment• Select a Kayrotype to analyze• Analyze

• Count Chromosomes• Determine Gender• Determine the chromosomal abnormality

• Write a Letter to the parents• Detailing procedure of amniocentesis or chronic villi sampling• Description of a “normal” karyotype• Description of their child’s abnormal karyotpe• Possible reasons for the abnormality• Associated characteristics resulting from abnormality• 2 actual support groups available for the family• Any other pertinent information• Be sensitive as if you were actually contacting real parents

Cell Cycle• Cell Cycle: repeating sequence of

cellular growth and division

• G0 – non dividing cells

• Interphase – growth and preparation› (90% of life):

G1 (1st growth phase) – cell grows and performs routine functions

S (Synthesis phase) – DNA is copied G2 (2nd growth phase) – Microtubules are

rearranged and cell prepares to divide

• Mitosis – Nuclear Division• PMAT

• Cytokinesis – division of cytoplasm

Interphase G1

› Gap -Growth and normal function S

› Synthesis -Chromatin duplicated, not yet visible

G2

› Gap -2 centrosomes form › Animal cells – each centrosome features 2 centrioles (microtubules arranged in a circle)

Chromosome Duplication

• During the S phase, each chromosome is duplicated via DNA replication

• This results in 2 chromatids attached at the centromere

Prophase• Chromatin condenses into visible

chromosomes

• Nucleolus disappears

• Microtubule spindles form asters around centrosome

• Microtubules move centrosomes to opposite poles of cell

• Nuclear envelope fragments

• Microtubules extend from centrosome to kinetochore of centromere

Metaphase• Centrosomes are at

opposite ends of the cell

• Chromosomes line up at midline or equator of cell

• Each kinetochore has a microtubule that extends to the centrosome called a spindle fiber

Anaphase• 2 sister chromatids separate

(becoming an individual chromosome)

• Chromatids move to opposite poles as microtubules (spindles) shorten

• Cell elongates

• By the end, the two ends of the cell each have a identical set of chromosomes

Telophase• Nuclear envelopes

and nucleoli reform

• Chromosomes become less condensed and thread-like

Animal Cells – cleavage furrow becomes visible

Cytokinesis - Animal Cells• Contractile ring

mechanism -microfilaments called actin pinch the plasma membrane of the cell resulting in a Cleavage furrow

Cytokinesis - Plant Cells• No contractile ring,

Why?• Cell walls stiff with

cellulose

• Vesicles (from golgi) fuse at midline to form cell plate

• Cell wall forms from cell plate separating the 2 new plant cells

Challenge Question

• Explain the structure and role of microtubules in animal cell division

• Hint: MTOC Mitosis Cleavage Furrow

• Pg 222-223 (cambell text)

Prokaryotic Cell Division

• Binary Fission: divides into 2 new daughter cells

• Also Asexual

Cell Cycle Control System• The timing and rate of cell division in various parts of an

organism are crucial to normal growth, development, and maintenance

• Molecules within the cell trigger and coordinate key events of the cell cycle• Checkpoint gene proteins can advance, delay or block the cell cycle

• Both internal and external factors can affect cell cycling

Checkpoints• Checkpoint – critical control point where “stop” and

“go” signals regulate the cycle (inspection station)• Regulation is influenced by environmental conditions• Stress (availability of nutrients)• Cell

• 3 major checkpoints:• G1 (Most important in animal cells)• Is this a dividing cell?• Is this cell healthy?• Is this cell large enough?• **If cell does not receive the “go” signal, it will switch into G0 non-dividing phase

• G2• Is DNA copied properly?

• M• Restarts cell cycle to G1 phase

Cell Cycle Checkpoints

Cancer • At the checkpoints

• Oncogenes – tell cell cycle to “go”• Tumor Suppressor Genes – tell cell

cycle to “stop”• If either of the genes that control the

cell cycle become mutated• Mutagens – cause mutations• Carcinogens – mutagens cause cancer

• The cell cycle goes too fast and divides out of control

• Cells pile up in one area and form a tumor• Neoplasm such as a mole – benign

tumor• Immune system does not recognize as

foreign • Benign tumor – does not invade

adjacent tissue• Malignant Tumor – cancer spreads and

new tumors form (metastasize)

Malignant Cancer• Grow and develop abnormally• Cytoplasm shrinks and

becomes disorganized• Plasma membrane becomes

leaky (altered or missing proteins)

• Metastasis – break away and establish new cell colonies in distant tissues

• Can be lethal without treatment• Chemotherapy, radiation, surgery,

or biotherapy