DNA structure and replication

Where is DNA located in the Cell?

What do we know about DNA?

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Inside the nucleus of every human cell is nearly 6 feet of DNA!

It can't be crammed into the nucleus like a ball of string.

Instead, it is combined with proteins and organized into a precise, compact structure, a dense string-like fiber called chromatin

•Each DNA strand wraps around groups of small protein molecules called histones forming a series of bead-like structures, called nucleosomes,

•Under the microscope, uncondensed chromatin has a "beads on a string" appearance.

•This compression and structuring of DNA serves several functions. The allows the DNA takes up much less space, and inactive DNA can be folded into inaccessible locations until it is needed.

DNA before Replication

DNA structure

DNA is made up of many nucleotides connected together

A nucleotide is made of:– Sugar (deoxyribose)– Phosphate– Base

• Adenine, Guanine, Thymine or Cytosine

SUGAR

Phosphate

BASE

DNA structure

The same bases always connect together

A — T and C — G

The order of the bases give the DNA its information or code

DNA always comes in two strands, like a ladder— it is called double stranded

DNA structure

In 3-D

DNA winds up in a double helix

How could you get DNA out of a nucleus?

How much DNA material could you retrieve from a strawberry?

What would the DNA look like?

What would you be able to see?

Purpose: Procedure: See Hand out Data:Observations

Copying DNA: DNA replication

Before the cell divides in Mitosis and Meiosis all of the DNA must be copied.

How?

Do you remember the basic form of DNA?

DNA ReplicationDNA needs to replicate itself to create more cells.Both body cells and sex cells

Steps to DNA replication

DNA is unwound and unzipped by enzymes The DNA code is read by DNA polymerase

(an enzyme) which adds the corresponding nucleotide (Nitrogenous base, sugar and phosphate)

Example Adenine is added to Thymine and Cytosine is added to Guanine

DNA before Replication

Both DNA Strands are read and a new identical DNA strand is created.

If the original DNA strand was ATCGCCGTTA The corresponding strand created would be TAGCGGCAAT

What strand would be created if the original strand was AAAACCGGATTT?

The strand would be TTTTGGCCTAAA You are so SMART!!!!!!!!!!!

Lets try a few more What DNA strand would be created from the following DNA strand?

AATTACGCGGCCC

Did you say TTAATGCGCCGGG

How about TATATACCGATTTA

Did you say ATATATGGCTAAAT

Great!!!

T The DNA Polymerase serves as a proof reader to correct any

mistakes that could occur Mistakes occur in 1/10,000

nucleotides added. An error creating a DNA could cause a disease to occur or the wrong directions given in another part of the cell.

Fun Fact… some people lack DNA polymerase.

They are more succeptable to getting cancer when DNA is damaged from exposure to UV rays.

How is the code read in the DNA to create proteins and give directions other places in the cell?

Transcription

The code to create proteins which lies in the DNA must be carried to a place where there are materials for the proteins to be created. Where are proteins created?

There is a Problem!!!! DNA is copied to mRNA because DNA is too

big to leave through the nuclear pores. It must be changed to something that can fit

through the nuclear membrane mRNA can do the job!!!!

mRNA is created RNA Polymerase opens the DNA molecule RNA polymerase looks for a specific code that

tells it when to start creating mRNA called a promoter

mRNA is created similarly to how DNA is replicated except mRNA does not have Thymine.mRNA Polymerase adds uracil to the mRNA strand instead of thymine to an adenine

The corresponding Nitrogenous bases are added as well as the sugar and phosphate attached.

Can you break the DNA code?

If the DNA sequence was ATTCGGCCATT what would the mRNA sequence be that was created?

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Did you say UAAGCCGGUAA Yeah!!

Lets try a few more

If the DNA sequence was ATTCCGCCGG

What would the mRNA sequence be? Did you say UAAGGCGGCC? How about TTCCGCGCGCCGAA? Did you say AAGGCGCGCGGCUU Great!!!

Translation: when proteins are made from the mRNAcode

The mRNA travels to the ribosome where the building materials are

TrNA (Transfer RNA) is great at breaking codes in the mRNA to make proteins

Proteins are made of Amino Acids There is a specific code for every three letter

nitrogenous base sequence in mRNA These three letter sequences are called codons. Each codon tells which amino acid to add to the

protein.

Three letter Codes are Codons.

For example….

GUU on mRNA signals a transfer rNA molecule to bring Valine a specific type of amino acid.

If the three letters were GCC the tRNA would bring Alanine and add it to the protein.

Just like building blocks make a wall,Different amino acids create a unique protein

This occurs at the ribosome

If I gave you the RNA sequence of CGGGUAUUAUGUGAAUGA what series of Amino Acids would be created into a protein?

Did you say Arginine,Valine,Leucine, Cytosine and Glutamine?

YOU ROCK!!!!!

Lets try one more….. If I gave you the MrNA strand of CGUAGUAGAAGGGCGUGA what Amino Acids would you bring together?Arganine, Serine, Argenine, Argenine,Alanine

FABULOSO!!!!!

Amino Acids connect to make proteins

Here is a great picture of the whole process….

To review, I will give you the player…. You will tell me what is does in the process and where it hangs out. First for DNA replication

DNA strand DNA polymerase

Now for transcription and translation

DNA strand Nuclear Membrane RNA polymerase MrNA TrNA Amino Acid Ribosome Codon Protein

Your Job…….

Create 2 comic strips: 1 comic must illustrate how DNA is created

for creating new cells It must include all major players involved They must talk about their role in the process

in your own words They must be pictured in the location they do

their job.

The other comic…. Illustrates transcription (Creation of mRNA)

and translation (Creation of a protein)(How mRNA is created and the code from a

DNA molecule allows a unique protein to be made)

This comic must represent each player involved….

Each player must talk about their individual role in the process

Each player must be located in the environment they do their job.

This will be due….

Next Friday You will have Friday as a work day and

some of Monday/Tuesday

Making Copies: DNA Replication

1. When DNA is copied, the rungs of the ladder break right down the middle, and pulls apart.

2. A protein: DNA polymerase, grabs onto new nucleotides and attaches them using the old DNA as a template

3. New bases are matched to the exposed bases on each strand, and the original DNA molecule becomes two new identical DNA

4. The result is two identical DNA molecules!!