DNA History, Structure, and Replication

DNA HISTORY, STRUCTURE, AND REPLICATION

Bellwork 1. List as many things from memory as you can about the

structure of DNA (example: it’s a long chain)

2. What is the procedure for getting absent work & making up your BW points when you’re absent?

3. Leave BW on desk to be stamped. Begin cutting your model pieces @ your lab table (15 minutes). Each person needs:

4 blue4 yellow1 green1 white1 pink1 purple

DNA Functions!

Deoxyribonucleic acid (DNA) has two major functions…

1)Store and use information to run the cell- the “brain”

2)To replicate (copy) itself for cell division

…and of course, to make you special!

Deoxyribonucleic acid

DNA Structure1. DNA is 2 long chains twisted

around each other

This creates a “double helix” shape (aka twisted ladder)

Draw a picture of a double helix in your

notes

Rosalind Franklin1920-1958

Hey, I figured that out!

Rosalind Franklin1952

Crystallized the DNA molecule

Took an X-Ray Photo of it•She concluded:•DNA is helical•DNA has “rungs”

Rosalind Franklin1952

Crystallized the DNA molecule

Took an X-Ray Photo of it•She concluded:•DNA is helical•DNA has “rungs”

On the back of your note taker summarize

Rosalind Franklin’s contribution to our

knowledge about DNA

DNA Paper Model

Can you arrange your pieces into 2 chains? Try it out! (think about what the flat/untwisted version of a double helix would look like)

DNA Structure2. DNA is made of 4 similar, but

different subunits

Each subunit is called a nucleotide. Nucleotides have 3 parts:• Deoxyribose (sugar)• Phosphate• Nitrogenous Base (A, T, G or C)

DNA Paper ModelTry to make 4 nucleotides out of your DNA

pieces. Think about what 3 things must be in EACH nucleotide.

A Nucleotide

Draw a picture of a nucleotide on your notes

Count

the

nucle

otide

s!

• A nucleotide is three things that work as one unit. (sugar, phosphate, N-base)

• We think of a hub, spokes, and a rim as a wheel. You can separate these parts, and take them apart one by one, but usually you find them together in a unit called a wheel.

DNA Structure

• Nucleotides are joined together with strong covalent bonds, forming long strands

Paper modelMake ONE strand of DNA down the left side of your paper (4 nucleotides long). Glue it into place once approved.

When you are finished, help someone else complete their paper model

Put your name on your paper model

• Circle ONE nucleotide

Closure

Write one complete sentence about what you learned for each letter:

D-N-A-

Sponge

• Nucleotide video (0:41): http://www.youtube.com/watch?v=PFYp9Gfg3Y4

• Rosalind Franklin video (2:24):http://www.youtube.com/watch?v=y6k1jpQIlEU

Bellwork 1. What is the scientific name for the subunits of DNA?

2. What are the 3 parts of each subunit?

3. Describe a time in your life when you had to use a code. Why did you need a CODE and how did it help?

4. Begin cutting your model pieces. For today you need another 4 blue, 4 yellow, 1 green, 1 white, 1 pink, 1 purple (15 mins)

DNA Structure3. The order of subunits on one strand

determines the order of subunits on the complementary strand

Chargaff’s Rule: On opposite strands, A always pairs with TC always pairs with G

Erwin Chargaff1905-2002

I got a rule named after me!

Erwin Chargaff 1950Took DNA samples & broke them apart

Analyzed the amount of each nitrogenous base (A,T,G,C)

•He concluded:

A = T

G = C

Erwin Chargaff 1950Took DNA samples & broke them apart

Analyzed the amount of each nitrogenous base (A,T,G,C)

•He concluded:

A = T

G = C

On the back of your note taker summarize Erwin Chargaff’s contribution to our knowledge about

DNA

Come up with a memory strategy for Chargaff’s Rule

A-T

C-G

Practice Chargaff’s Rule

On your note taker, complete the second strand of DNA using Chargaff’s Rule

Chargaff’s Rule

• Label the deoxyribose sugars with “D”

• Label the phosphates with “P”

• Circle one nucleotide

D D

D

D

D

D

D

D D

D

D

D

D

D

DD

P

P

P

P

P

P

P

P

P

P

P

P

P

P

P

P

DNA StructureThe two strands are held together by

weak hydrogen bonds between the nitrogenous base-pairs.

•Label one of the

hydrogen bonds on

your Chargaff’s

Rule picture

Paper modelUse Chargraff’s rule to make a complementary

strand of DNA & connect it to the first strand. Glue it down once approved. After you

finish, help other students finish their models.

• What do you notice about

the complementar

y strands?

James Watson and Francis Crick 1953

We won the Nobel

Prize!

Watson and Crick 1953-Used all info & Franklin’s photograph & Chargaff’s Rule to accurately model the structure of DNA (just like you did!)

-Included double helix with “rungs”

-“Rungs” held together by Hydrogen Bonds

Watson & Crick shared the Nobel Prize for the discovery of DNA structure

On the back of your note taker summarize James

Watson & Francis Crick’s contribution to our knowledge of DNA

Closure: How is DNA like a piece of yarn?

Write a PIE paragraph response in your notebook.

Give specific examples.

Bellwork Have slate, marker & eraser on desk

1. What is the scientific name for the “subunits” of DNA?

1. What are the 3 parts of each subunit?

2. What is Chargraff’s Rule?

3. Copy the strand of DNA on the right and write the complementary strand next to it, using to Chagfraff’s Rule.

4. Write one note about each of the following scientist’s contributions: Franklin, Chargaff, Watson & Crick

AGTCAATGCG

TCAGTTACGC

DNA Replication

DNA Replication

DNA copies itself in 3 steps

Step 1- DNA Unzips• DNA Helicase (enzyme) splits apart

the two chains of DNA

Draw a picture of step 1 on

your note taker

• What is the first step of replication?

• Please unzip the two chains of your DNA model

• What did the scissors represent while we unzipped the model?– DNA Helicase

• Each strand acts as a pattern or template for the new strands

• DNA Polymerase takes free nucleotides makes new strands using Chargaff’s Rules

Step 2- Bases Pair Up

Draw a picture of step 2 on

your note taker

• What is the second step of replication?

• Please draw the complementary strands for each of the parent chains

• What does parent chain mean?

• What could we call the new chains if the original ones are called “parents”?

• What represented the DNA polymerase enzyme when we made the new strands?

• Enzymes double check new daughter strands for errors, & fix if needed

• Sugar-phosphate backbone bonds tightly

Step 3- Check & Bond

Draw a picture of step 3 on

your note taker

• What is the third step of replication?

• Please glue the strands together and double check for errors in your 2 new sets of DNA

• What represented the enzymes that double check for errors in your model?

• This DNA replication process is so accurate that errors are rare (1 in a billion) and when errors do occur they are often corrected by special repair enzymes. This repair allows for accurate replication as organisms grow and reproduce generation after generation.

• If you did a task once every minute for the rest of your life, and made that few mistakes, you would only make one mistake every 30 years!

Label your model

• Put your name at the top of your two new sets of DNA

• Label the parent strand, and label the daughter strand

• Circle and label a nucleotide on one of the daughter strands

Homework- due Friday1. Replicate the other parent strand using

the 3 steps

2. Label the parent strand & daughter strand

3. Label a nucleotide on the daughter strand

Closure

How would you explain the process of DNA replication to a 1st grader?

Write out a short paragraph in simple language and include simplified drawings (little kids often understand drawings better than words).