DNADeoxyribonucleic Acid

Chapter 11

Page 287

What is DNA?

The information that determines an organisms traits.

DNA produces proteins which gives it “The power”

Many things contain and are made of proteins.

Skin, hair, bones, etc are made of proteins.

What is DNA? Cont’d

Enzymes are special proteins. Enzymes control chemical reactions

needed for life. DNA contains all the information for

making all and any proteins for human life.

DNA Structure: DNA is made of

repeating subunits called nucleotides.

Nucleotides have three parts:– Simple sugar– Phosphate group– Nitrogen base

DNA Structure The simple sugar is called deoxyribose. The phosphate group is made of

phosphate and oxygen. There are four possibilities to Nitrogen

bases:– Adenine (A)– Guanine (G)– Cytosine (C)– Thymine (T)

DNA Nucleotides join together

to form long chains. The phosphate group of

one nucleotide joins together with the deoxyribose sugar of an adjacent nucleotide.

The phosphate groups are thought of as the “backbone” of the chain

The nitrogen bases are thought of as teeth coming off the structure.

DNANitrogen bases

Nitrogen bases pair up– Adenine

and Thymine (A-T)

– Cytosine and Guanine (C-G)

Watson and Crick

First people to propose that DNA is made of two chains of nucleotides joined together by the nitrogen bases

They believed that the two strands are joined by complimentary bases

• A-T• C-G

They also proposed that DNA is put together like a zipper that is twisted.

When something is twisted like a spring, it is called a helix.

Because DNA has two strands it is called a Double Helix.

Importance of Sequencing

The sequence of the four different nucleotides determines what organism is created.

For instance – T-A-A-G-C-A Is different than – A-G-C-A-A-G

In English - E-A-R-T-H Is different than H-E-A-R-T– They have the same letters, just a different order

and mean different things.• Can you think of any other words that you can do this

with?

The closer the order is to another order, the closer the relationship between the two organisms.

Importance of Sequencing

Scientists can use the sequencing to find out evolutionary history.

For instance, gorillas and chimpanzees might have similar sequencing but chimpanzees and rose bushes would not be very similar.

DNA sequencing can also be used to show whether two people are related or not.

DNA sequencing can also be used to correlate someone to a crime scene.

END OF DAY 1

DNA Replication

DNA is copied – this is called replication

Without DNA replication, a new cell would only have half of it’s information.

All organisms undergo DNA replication

DNA Replication

Replication VIDEO

DNA Replication

Because of the pairing- if you have one strand, it is easy to predict the replicated strand.

T-A-G-C-C-G-T Would be replicated by matching T, with

A, G with C A-T-C-G-G-C-A

DNA Replication Remember: The nitrogen bases are held

together by hydrogen bonds There is an enzyme that goes to those

hydrogen bonds and breaks them This causes the double helix structure to break

apart or “Unzip” There are nucleotides that are floating around. These nucleotides are like puzzle pieces They each try to attach to the original

nucleotide.

DNA Replication

The unzipping continues until the entire strand is done.

The original DNA now has a complimentary strand.

The result is two DNA molecules which is identical to the original.

The end product is that there are two copies of the organism’s genetic makeup.

DNA to Protein

DNA encodes the instructions for making proteins.

Remember proteins make up your bones, skin, etc.

Enzymes are special proteins Enzymes control all chemical reactions

in an organism

DNA Replication

Proteins are made up of many amino acids

The order of nucleotides in each gene has information on how to make the string of amino acids which is a protein.

ESTIMATE: Each cell contains about 800,000 genes

RNA There are three key differences between

RNA and DNA1. RNA is single stranded – only half of a

zipper – DNA is double stranded – zipper

2. RNA is made of the sugar Ribose – DNA is made of deoxyribose

3. RNA has Uracil instead of Thymine – Both DNA and RNA have four nitrogen bases the difference is U vs T

RNA RNA has the job of copying DNA The goal of RNA is to create proteins There are three types, each with a

different job.– mRNA – Messenger RNA-copies DNA to

take it out in the cytoplasm– rRNA – Ribosomal RNA-works on

matching mRNA - to create the amino acids in the correct order

– tRNA – Transfer RNA- gives amino acids to rRNA to produce the protein.

mRNA

Messenger RNA is responsible for uncoding the DNA and creating RNA (in a process called transcription) for mRNA, rRNA, and tRNA to read.

Messenger RNA is responsible for bringing the information transcripted RNA to the cytoplasm.

WHY in the cytoplasm?

rRNA Ribosomal RNA are made of

ribosomes. Where are ribosomes found?

– In the cytoplasm. They are not bound to any one organelle.

rRNA attaches to the mRNA rRNA then begins to use the information

from DNA that mRNA brought out. rRNA uses the information to set up the

amino acids in the correct order.

tRNA

tRNA is the supplier tRNA gives amino acids to rRNA so that

rRNA can assemble the protein.

Review Questions

How does information from the DNA get to the cytoplasm?

How does the zipper get unzipped in DNA replication?

Who does the work in getting the amino acids to the worker?

What is the formal name of the worker

END OF DAY 2

Transcription Transcription’s purpose is to create a

single stranded RNA molecule rather than a double stranded DNA molecule.

This is needed to allow the single stranded RNA to be taken out of the nucleus by the mRNA to the cytoplasm.

Transcription

Transcription Tutorial / SHOW

Transcription mRNA VIDEO

Genetic Code with mRNA

In order to take the DNA and create a mRNA, there are special codes used.

In mRNA, three nitrogen bases together form a code – this is called a codon.

Looking ahead: this code is matched with an amino

acid. A string of amino acids form a protein.

Genetic Code with mRNA

Some codons code for information other than amino acids

UAA is an example of a stop codon. AUG is an example of a start codon. NOTE: For every one codon, there is

only ONE amino acid that can join.

Transcription Pictures

Transcription Pic’s

How does this work in the cell?

DNA

AMINO ACIDS TRANSPORTED BY tRNA

mRNA COPIES DNA INTO CYTOPLASM

rRNA USES PLAN FROM mRNA TO PUT AMINO ACIDS IN ORDER TO MAKE PROTEINS RIBOSOME

NUCLEUS

END OF DAY 3

Translation: From mRNA to Protein

The process of changing the information from an order of nitrogen bases in mRNA into the order of amino acids is called translation.

This takes place at the ribosomes in the cytoplasm

Translation

When mRNA enters the cytoplasm, ribosomes attach

For proteins to be made-20 different amino acids must be brought to the ribosomes.

This is what tRNA does – brings the amino acids to the mRNA strand

Translation

On the opposite side of the tRNA amino acid side is a set of three nucleotides that are the complement of the nucleotides codon.

Translation

These three nucleotides are called anticodons because they bond to the codon of the mRNA

The tRNA is made of only the anticodon and the amino acid.

Translation

When a match is made- a temporary bond is formed.

This places the amino acid in the correct position to enable it to bond with the next amino acid

Translation

The next tRNA bonds to it’s codon and then the two amino acid’s bond together.

The first amino acid then releases itself from the mRNA

Translation

This continues until a stop codon is reached.

Amino acid chains then become proteins when they are freed from the ribosome and twist and curl into complex three-dimensional shapes.

Translation

Translation VIDEO