A. Chromosomes are made of DNA

B. Segments of DNA code for a protein

C. A protein in turn, relates to a trait or a gene (examples: eye color, hair color, enzymes, hormones…)

I. How do chromosomes lead to specific traits?

How do we get proteins from genes (coding DNA)?

Let’s find out:

http://www.wisc-online.com/objects/index_tj.asp?objID=AP1302

• I.Structure and Function of RNAA) Why is RNA needed?

1) proteins are made by ribosomes outside the nucleus (on the rough Endoplasmic Reticulum)

• 2) DNA cannot leave the nucleus (it’s stuck) 

• 3) RNA is needed so that it can carry the genetic code (DNA) needed for making proteins to the ribosomes

• B)What is RNA?• 1) RNA - Ribonucleic Acid

a) the sugar in RNA is ribose 

b) in RNA the base thymine is replaced with URACIL.

• 2) There are 3 kinds of RNAa) r RNA - Ribosomal RNA- makes up ribosomes

 b) mRNA- messenger RNA-carries the genetic code out of

the nucleus to the ribosomes

c) tRNA- Transfer RNA- transfers amino acids to the

ribosome in order to make proteins

• II. RNA Codea) mRNA carries the code for an amino acid in a series of 3 nucleotides (like DNA triplet)

 b) A group of 3 mRNA nucleotides is called a codon.

  c) A group of 3 tRNA nucleotides is called an anti-codon (opposite of the codon)

ex. mRNA codon = UAG tRNA anti-codon = AUC

d) The genetic code is universal - codons code for the same amino acids in all known life forms

• Protein Synthesis is a two part process

• 1) Transcription (in the nucleus)• 2) Translation (in the cytoplasm)

• III. Transcription - mRNA is copied from DNA• Steps:

1) DNA unzips2) RNA nucleotides bond to the

exposed bases on the DNA strand

(note: transcription is similar to DNA replication except in RNA adenine pairs with uracil)

3) Transcription continues until a stop” codon is reached

• IV. Translation - mRNA is used to make protein

• Steps:1) mRNA leaves the DNA in the

nucleus and travels to a ribosome

2) the ribosome begin “translating” the mRNA into protein when it reaches a “start” codon

  3) the ribosome”translates” the mRNA into a sequence of amino acids that make up a specific protein

4) Translation continues until a “stop” codon is reached.

V. How do the Ribosome do their job?1) tRNA is the key

2) What is tRNA?tRNA carries an aminoacid on one end. Theother end contains theanti- codon (threenitrogen bases) that willmatch up with the mRNAcodon. 

3) tRNA molecules match their anti-codon to the mRNA codon

4)A protein is formed as tRNA’s release their amino acids which bond together to make a

protein(peptide bond)

mRNA Ribosome

Protein

(amino acid chain)

• All of the proteins in your body are made up of combinations of only 20 different amino acids linked together in different ways.

• (see codon chart)

Th

ird L

ette

r

• TRANSCRIPTION(in the nucleus)– 1. DNA helix

opens– 2. mRNA chain is

copied from DNA

• TRANSLATION(in the cytoplasm)

1. mRNA attaches to a ribosome in the cytoplasm2. tRNA molecules carrying amino acids match anti-codon to mRNA codon

3. Amino acids are released and bonded together to make a protein.