DNA replication

BIG IDEA

• Living systems store, retrieve, transmit and respond to information essential to life processes.

Enduring understanding

• Heritable information provides for continuity of life.

• Essential Knowledge:– DNA is the primary source of inheritable info– In eukaryotes, heritable info is passed on the next

generation via processes that include the cell cycle and mitosis and meiosis plus fertilization.

– The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring.

1. How was the structure of DNA identified?

2. Erwin Chargoff: *Chargoff’s rule : The proportion of adenine equals that of thymine, and guanine equals that of cytosine -- therefore, purines are proportionate to pyrimidines

Homework

• Read p. 241- 243…be prepared to write out the answers to questions 1-4 on p. 243 in class tomorrow.

• Take notes for a quiz on p. 295-299.

1. Why do cells divide?

2. Surface area to volume ratio is not large enough

* cells cannot move molecules in/out effectively

2.Cells are used to repair tissue damage

2. DNA overload if it gets too big

2. Organisms develop and grow

1. Why & how does DNA replicate prior to cell division?

2. Cells need to transmit their DNA to cells

* body cells (somatic cells) need to be identical to parent cell

* sex cells (gametes) need to pass 1/2 genetic material to offspring

2. DNA is the genetic code within chromosomes

* DNA is wrapped tightly around proteins (histones) = nucleosome

* Nucleosomes are looped and coiled to make chromosomes compact

* Chromatin is the “substance” of DNA & histones

Refer to page 297 of textbook

2.Cells replicate their DNA

* Occurs during the S (synthesis) phase of the Cell Cycle

2. Steps to DNA semi-conservative replication

* DNA unzips (helicase)

* DNA polymerase joins newnucleotides to form newstrand

* Replication goes inboth directions

Practice replication

3’ A T G C A G 5’

5’ T A C G T C 3’

2. Other jobs of DNA polymerase

* connects sugars to phosphates

* proofreads DNA.

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120076/micro04.swf::DNA Replication Fork

DNA replication video animation

• 2. cell must copy lots of DNA quickly 3. solution: multiple origins

2. telomeres shorten with cell divisions....adult cells stop using telomerase.....cancer cells keep telomerase working......FOUNTAIN OF YOUTH?

Think about this.

• Why do cells divide?

• When do cells replicate their DNA?

• Do organisms grow by getting bigger cells? Or more cells?

• How does a lizard regrow a tail?

Romanovs mDNA

http://www.dnai.org/d/index.html?m=2,1

PCR- a technique used to copy DNA

• http://www.dnalc.org/resources/animations/pcr.html

Refer to iPad- tutorial w/shoelacesreflection p. 485

• PREVIEW OF MITOSIS/– Listen to vocabulary

1. What is the cell cycle of a cell?2.  

Interphase: stage 1 

G1 - growth, protein synthesis, general cell functioning

S - DNA is replicated

G2 - cell prepares for division

2.Mitosis (nuclear division)

a. Prophase – chromosomes condense - chromatids visible -nuclear membrane dissolves

• • b. Metaphase - chromatids line up along

middle of cell (equator)

c. Anaphase - chromatids pull apart to opposite poles of cell (spindle fibers made in G2 pull chromatids apart)

d. Telophase - nuclear membranes reappear, cell pinches in to divide in plants the cell plate (wall) forms

Cytokinesis• Cell continues to pinch in & cytoplasm

divides out—2 new daughter cells are made… both have identical copies of the chromosomes

Review of cell cycle

Tutorial

http://sciencenetlinks.com/interactives/dna.html

Online tutorials

• http://district.bluegrass.kctcs.edu/rmccane0001/shared_files/bio137website/BIO137/137Lab2/Lab2MitosisSlides.html

Create a table

• Create a two column chart.

• Column one- describe what is happening• Column two- sketch the image…

1.How do cells regulate the cell cycle?

• 2. Cells stop growth when they come in contact with one another

• 2. Regulatory proteins (cyclins) * Check to see that DNA is replicated *Check to make sure spindle fibers are attached

2. Growth factors stimulate/stop cell division

Analyze Rise & Fall of Cyclins

• iPad p. 491 parrot book

• 2. Apoptosis- programmed cell death

– * forms body parts- foot, hand…– * cells die if there is a problem (usually)– * too much cell death- Parkinson’s disease

• 2. Cancer is uncontrolled cell growth– *cells don’t respond to regulators– * p53 gene is often defective (pro-oncogene)

Cancer knows no bounds

Timeline

• 1. notes: why do cells divide? & how does DNA replicate?

• mtDNA/Romanovs & PCR computer lab.

• Notes: cell cycle/color code sheet…

• Online mitosis (full period)

• Notes: cancer/stem cells & cell regulation

• 1. Give 2 reasons why cells divide.• 2. As a cell increases in size, which increases

more rapidly, its surface area or volume?• 3. Calculate the surface area to volume of a

cube 2 x 2 x 2.

• 4. Do prokaryotic cells have a nucleus?• 5. What are the proteins that DNA is tightly

coiled around?• 6. What is chromatin?• 7. The process of DNA copying is called:• 8. The enzyme responsible for copying DNA is

called: