C & C P. 2291. Explain why neither cyclins nor kinases alone can cause a cell to

progress through the cell cycle.Interaction of cyclins and kinases is required for regulation

2. How do controls on the cell cycle protect multicellular organisms from accumulating large numbers of damaged or defective cells?The cycle can be paused (cell-cycle arrest) so that damaged DNA can be repaired.

3. What is the difference between a cancerous tumor and metastasisMetastasis involves the breaking off and movement of cells from the primary tumor to another location in the organism.

4. What are the functions of tumor-suppressor genes and proto-oncogenes in noncancerous cells?They serve key roles in regulating many cellular processes, including cell division, where proto-oncogenes promote cell division and tumor-suppressor genes inhibit cell division.

DNA: The genetic material

A few questions to ponder today:• What is DNA?• How did we figure out the

structure of this important biomolecule?

• How is it replicated for the cell cycle?

• Steps to the discovery of DNA:– 1869- Freidrich Miesher

• purified DNA from pus cells obtained from discarded surgical bandages

– 1923- Robert Feulgen • developed a procedure that stained this material in the nucleus• This enabled him to measure the amount of “stuff” in the

nucleus• He concluded that virtually every cell nucleus in any plant or

animal has the same amount of this “stuff”

What was this “stuff” found in the nucleus and did it have anything to do

with why offspring look like their parents?

Was it DNA or a protein that carried the hereditary instructions from

generation to generation?Early scientists saw the structure of the DNA molecule as too simple to possibly contain the complex genetic information of an organism

• 1828- Fred Griffith was working on a project that enabled others to point out that DNA was the molecule of inheritance.

• He was trying to prepare a vaccine against a pneumonia-causing bacterium.

• He discovered that harmless bacteria could turn virulent when mixed with bacteria that caused disease.

• In other words, he discovered what was called transformation

a change in phenotype caused when bacteria cells take up foreign genetic material. animation

• 1944- Oswald Avery– continued with Griffith’s experiment to see what the inheritance molecule was. – In his experiment he destroyed the lipids, ribonucleic acids, carbohydrates, and

proteins of the virulent pneumonia. – Transformation still occurred after this. Next he destroyed the deoxyribonucleic

acid. Transformation did not occur. Avery had found the inheritance molecule, DNA! • 1952- Alfred Hershey and Martha Chase settled the controversy.

– DNA is the molecule that store genetic info in living cells

animation

• 1951- Roseland Franklin fired x-rays through DNA crystals, trying to learn how the atoms of the DNA molecule were arranged

• 1953- James Watson and Francis Crick were shown Franklin’s photo and immediately determined the double helical structure of DNA.

Deoxyribonucleic Acid

Phosphate molecule

Nitrogen Base molecule

Sugar molecule

Hydrogen bonds

GuanineAdenine

CytosineThymine

DNA StructureNucleotides are the subunits:

– a phosphate group– a 5-carbon sugar molecule

• Deoxyribose• 5’ end• 3’ end

– a nitrogen –containing base• Purines- made up of 2 rings of carbon

and nitrogen atoms– Adenine (A)– Guanine (G)

• Pyrimadines- made up of a single ring of carbon and nitrogen atoms

– Thyamine (T)– Cytosine (C)

Chargaff’s Rule- (1947)- Erwin Chargaff, a chemist who worded at Columbia

found that:– for each organism studied, the amount of adenine

always equaled the amount of thymine – and cytosine always equaled guanine. – This became known as the Base-Pairing Rules

Why does this complementarity exist?□ The two chains of nucleotides are held together

by 2 or 3 weak hydrogen bonds that form between the nitrogenous bases:– Cytosine and guanine have three hydrogen

bonds– Thymine and adenine have two hydrogen

bonds□ Each rung of the DNA ladder needs to have a

total of three rings • Also, One of the strands of DNA runs in the 3’

to 5’ direction and the other runs in the 5’ to 3’ direction.

• This is called _______________antiparallel

DNA cont.• DNA is the molecular

“blueprint”—– This “instruction manual”

makes up an organisms genes. – Encoded in the precise order of

its nucleotides – The genetic alphabet only

contains 4 letters (ACTG). – Human DNA contains more

than 3 billion base pairs!

COMPARING PROKARYOTIC AND EUKARYOTIC DNA:

PROKARYOTES EUKARYOTES

Configuration of DNA Circular linear

Length 1000 micrometers 1.8 meters

DNA housed in nucleus?No Yes

Associated proteins Transient proteins Histones

# of Chromosomes per Cell

1 2- 1,262

HOW DO ALL THESE BASE PAIRS FIT IN THE NUCLEUS?

– a NUCLEOSOME consists of 2 loops of DNA wrapped around a central cluster of 8 histone molecules.

– This shortens the length of DNA by 1/6. – This is shortened even further by its coiling into

thicker fibers

• Complete the Concept Map in your packet • Begin “Journey into DNA”• Finish crossword puzzle and any of the above

for homework