Bellwork Monday 12/5* If you were absent last Friday, come in during tutorial to take test*Finals next Thursday and Friday 12/15 and 12/16*We will do a big review packet that you can use on the final

1. What does DNA do? (If you have no clue, give it your best shot or ask your neighbors)

Agenda:

1. Pass back tests

2. Whiteboards

3. Notes

Whiteboard reminders

• Please only write answers to the questions

• Please clean your whiteboard when you are finished

• Please throw away all paper towels

Whiteboards*No worries if you are unsure on these, give them

your best shot!1. What is the function of DNA in cells?2. Where did your DNA come from?3. Draw the structure of DNA, in as much detail

as you can.4. Why is DNA called a double helix? 5. What are 3 parts of a DNA molecule?6. How do cells copy DNA *Bonus: What does DNA stand for?

DNA• instructions for cells

• the Genetic Code

• passed to new cells & offspring

Dr. Watson! (And Dr. Crick)

DNA Structure• 3 parts

– Deoxyribose (a sugar)

– Phosphate (a mineral)

– Nitrogen-containing base

• 4 types of bases– Adenine – A

– Guanine – G

– Cytosine – C

– Thymine – T

• DNA molecule shape is a double helix – Like a twisted ladder– Sides of Ladder

• Formed by sugar + phosphate• “Sugar-phosphate backbone”

– Rungs of Ladder• Formed by pairs of bases

• Base Pairs– A pairs only with T

– G pairs only with C

• Double helix can be split into two strands

• 2 strands are Complementary– Like 2 halves of a dollar bill

• 2 strands are important– As a back up– Makes duplicating chromosomes easy

DNA facts

The percent of your DNA you have in common with:

• Another person in this room- 99%• A chimpanzee- 97%• A dog- 75%• A banana- 50%If you stretched all the DNA in all of you cells, it

would reach the sun and back 4 times!The DNA in each cell contains roughly 3GB of

storage

DNA Model (phase 1)• Use templates of deoxyribose, phosphate and the 4 bases to make cut outs.• Need: 6 deoxyribose

6 phosphates 6 bases that will make 3 pairs

• Alternate deoxyribose & phosphate for 2 backbones– Note that one backbone is upside down

• Pair bases in between for “rungs”– Note that one base must be turned upside down to match

• Glue them down.

DNA Replication4 Steps

• 1) DNA molecule “unzips” – Double helix separates

between base pairs

• 2) each single strand acts as a template

& is copied

• 3) Result:– 2 identical double strands

– Both identical to original DNA

– Each has 1 new &

1 original strand

• 4) Errors are corrected– An enzyme slides along new strand– Compares it to original strand– Fixes any mismatches in new strand– Errors in mitosis can lead to cancer

• Complementary base pairs

Original DNA: C G G A T C A G T

Complementary: _ _ _ _ _ _ _ _ _

A – TG - C

DNA Model (phase 2)Replication

• Unzip (cut) between the base pairs

• Get a second sheet of paper to add to middle

• Need: 6 more deoxyribose

6 more phosphates

6 more bases (like last time)

• Arrange 2 new sugar-phosphate backbones in center

• Add new complementary bases to each side

• Check for errors

• Glue them down