DNA: A Look Back

Contents of the Nucleus

DNA vocab

• Deoxyribonucleic acid

• Chromosomes• Chromatin• Genes

DNA Structure

• What is the structure called?

Building blocks of DNA• What are the building blocks of DNA? • What are the building blocks made of? (3

parts)

• How do they fit together?

• What is the significance of the order of the nitrogenous bases?

Try “replicating” this single strand of DNA

DNA --> Chromosomes

• http://www.youtube.com/watch?v=E8NHcQesYl8&mode=related&search=

Human set of Chromosomes

Fruit fly Chromosomes - only 8!

-What are chromosomes?

-What do they store?

-How many do we have?

-Where did they come from?

Genes -WHAT are they?

-WHERE are they?

Enzymes

• WHAT are they?• What do they do? • Why do our DNA molecules store the

instructions to make them?

Genetic Material: DNA vs RNA -

compare and

contrast.

RNA is composed of 3 parts:

• Ribose – a smaller sugar than deoxyribose• Phosphate• Nitrogenous Bases

-adenine, uracil (instead of thymine), guanine, and cytosine

RNA is single-stranded and thus smaller and able to leave the nucleus of the cell

Protein Synthesis

STEPS

1. Transcription

2. Translation

Step 1: Transcription

• Takes place in the nucleus• Process by which information from DNA is

transferred to RNA• DNA uncoils and unzips• The exposed DNA bases are matched up with

RNA bases to form mRNA (messenger RNA)

Try transcribing this piece of DNA

into mRNA

Step 2: Translation

A U G G G C U U A A A G C A G U G C A C G U U

This is a molecule of messenger RNA (mRNA). It was made in the nucleus by transcription from a DNA molecule.

mRNA molecule

codon

A U G G G C U U A A A G C A G U G C A C G U U

The mRNA molecule attaches to a ribosome on the rough endoplasmic reticulum.

ribosome

A U G G G C U U A A A G C A G U G C A C G U U

It brings an amino acid to the first three bases (codon) on the mRNA.

Amino acid

tRNA molecule

anticodon

U A C

A transfer RNA molecule arrives.

The three unpaired bases (anticodon) on the tRNA link up with the codon.

A U G G G C U U A A A G C A G U G C A C G U U

Another tRNA molecule comes into place, bringing a second amino acid.

U A C C C G

Its anticodon links up with the second codon on the mRNA.

A U G G G C U U A A A G C A G U G C A C G U U

A peptide bond forms between the two amino acids.

Peptide bond

C C G U A C

A U G G G C U U A A A G C A G U G C A C G U U

The first tRNA molecule releases its amino acid and moves off into the cytoplasm.

C C G U A C

A U G G G C U U A A A G C A G U G C A C G U U C C G

The ribosome moves along the mRNA to the next codon.

A U G G G C U U A A A G C A G U G C A C G U U

Another tRNA molecule brings the next amino acid into place.

C C G

A A U

A U G G G C U U A A A G C A G U G C A C G U U

A peptide bond joins the second and third amino acids to form a polypeptide chain.

C C G C C G

A U G G G C U U A A A G C A G U G C A C G U U

The polypeptide chain gets longer.

G U C

A C G

The process continues.

This continues until a termination (stop) codon is reached.

The polypeptide is then complete.

The Code:

• How do you follow the mRNA code?

• Video on Protein Synthesis (includes tRNA)

• http://www.youtube.com/watch?v=NJxobgkPEAo&mode=related&search=

Try “DECODING” this piece of DNA Code

DNA T A C G G A C A G T A A T T C

mRNA

Amino acids

DNA T A C G G A C A G T A A A T T

mRNA A U G C C U G U C A U U U A A

Amino acids

Methi-onine

proline valine isoleucine

stop

• Read p. 131 of textbook

• Where does the

protein go from here?

• How does it get there?

• What are the names of the containers that come off of the ER?

• Where do they go?

Exiting the Cell

One Gene = One Protein?

• Human genome = approximately 25,000 genes

• Number of proteins humans make is approximately 90,000.

• NOT SURE HOW THIS CAN BE!