Cell Cycle6.4 – 6.9

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The Cell Cycle alternation of activities between cell division

and other processes  describes series of phases leading to cell

division mitosis and three phases of interphase—Gap

1, DNA synthesis, and Gap 2 cell division phase – mitosis phase of growth and non-reproductive

activities – interphase

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In which part of the cell cycle does the cell spend most of its time?

1. Interphase2. Mitosis3. G24. DNA synthesis

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DNA Review DNA = deoxyribonucleic acid long, spiraling “ladder” with a sugar-

phosphate backbone Four bases – thymine (T), adenine (A),

cytosine (C), guanine (G) form the “rungs” of the DNA ladder. (2 bases form a rung -- one for each side of the ladder)

Sugar + base + phosphate = nucleotide

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Chromosome Structure Single strand of DNA

forms a chromosome DNA is wrapped

around spools of a protein called histone

Therefore, DNA is much, much longer than the chromosome it makes up

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DNA Replication Copy double-stranded DNA Necessary for cell division Replication is termed semiconservative

since each new cell contains one strand of original DNA and one newly synthesized strand of DNA

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DNA Replication Special enzymes move up along DNA

ladder and “unzip” the molecule as it moves along

New nucleotides move in to each side of the unzipped ladder

Cytosine (C) pairs with guanine (G), adenine (A) pairs with thymine (T).

Arrangement of bases is what determines genetic code

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DNA Replication When enzyme has passed the end of the DNA,

two identical molecules of DNA are left behind Each contains one side of the original DNA

and one side made of "new" nucleotides It is possible that mistakes were made along

the way -- in other words, that a base pair in one DNA molecule doesn't match the corresponding pair in the other molecule

On average, one mistake may exist in every billion base pairs

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Mutation Variety of errors can occur during

replication Several DNA repair processes occur after

replication If error remains sequences in a replicated

DNA molecule (including the genes) can be different from those in parent DNA molecule

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Review: If an incorrect base is placed in the DNA during replication, the mutation would be called a:

1. deletion2. insertion3. substitution4. chromosomal breakage

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Reason for Mitosis To enable cells to generate

new, genetically identical cells – why? 1. Growth2. Replacement

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Apoptosis Apoptosis : Pre-planned cell “suicide”

called apoptosis parts of body where the cells are likely to

accumulate significant genetic damage over time, high risk of becoming cancer cells

cells lining the digestive tract, liver, etc cells are almost constantly in contact with

harmful substances

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Mitosis # of (somatic) cells that must be

replaced by mitosis every day is huge Rate @ which mitosis occurs varies

dramatically average RBC ~ 6 weeks cells lining the intestines ~ 3 weeks hair follicles also divide rapidly

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What cellular process listed below might involve mitosis?1. Wound healing2. Making insulin3. Glucose transport4. Muscle contraction

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Mitosis – Overview Parent cell duplicates DNA duplicate

copy of each chromosome Remaining organelles duplicate Cell divides into two new duplicate cells

(daughter cells) Usually the shortest period in eukaryotic

cell cycle

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Mitosis – Overview

Interphase In preparation for mitosis, chromosomes

replicate DNA synthesis (S) part of interphase, every

chromosome creates an exact duplicate of itself by replicating

Before replication, each chromosome was a single long linear strand of genetic material

After replication, each chromosome is a pair of identical long linear strands, held together at the center, a position called the centromere

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Interphase

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Sister Chromatids

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Mitosis – The DetailsProphase

chromosomes condense, coil, become visible

official beginning of mitosis

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Mitosis – The DetailsProphase

chromosomes condense, coil, become visible

official beginning of mitosis

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Mitosis – The Details Metaphase

chromatids separate and move in opposite directions

Anaphase pairs of sister chromatids are all

simultaneously pulled apart by the spindle fibers

one full set of chromosomes goes to each side of the cell

chromosome sets will eventually reside in nucleus of new daughter cells

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Mitosis – The DetailsTelophase

New nuclear membranes re-form around the two complete chromosome sets.

chromosomes begin to uncoil and fade from view

nuclear membrane is reassembled cell begins to pinch into two

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Cytokinesis cell’s cytoplasm is also

divided into approximately equal parts

some of organelles go to each new cell

two new daughter cells (each w/identical nucleus) enter interphase

Cancerunrestrained cell growth and

divisioncan lead to tumorssecond leading cause of death

in the United States (heart disease is #1)

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CancerDisruption of DNA in a normal cell

interferes with cell’s ability to regulate cell division caused by :

chemicals that mutate DNAsources of high energy (X-rays, sun,

nuclear radiation)viruses

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Cancer

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Cancer: Benign vs. MalignantBenign tumors (moles, warts,

etc.)masses of normal cells that do

not spreadusually be removed safely

without any lasting consequences

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Cancer: Benign vs. MalignantMalignant tumors

cancerousgrow continuously shed cells

shedding of cancer cells from malignant tumors is how cancer spreads (metastasis

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Cancer TreatmentRapidly dividing cells must be removed

surgically, killed, or slowed downChemotherapy

anti-mitoticdrugs are administered that interfere w/cell division.

Slows growth of tumors, but because the drugs interfere with cell division throughout the body they have terrible side effects.

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