I. How do chromosomes lead to specific traits?
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…)
How do we get proteins from genes
(coding DNA)?
Let’s find out:
http://www.wisconline.com/objects/index_tj.asp?objID=AP1302
• I.Structure and Function of RNA
A) 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 RNA
a) 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 Code
a) 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 unzips
2) 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 amino
acid on one end. The
other end contains the
anti- codon (three
nitrogen bases) that will
match up with the mRNA
codon.
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)
Protein
(amino acid chain)
mRNA
Ribosome
• 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)
Third Letter
• 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
cytoplasm
2. tRNA molecules
carrying amino acids
match anti-codon to
mRNA codon
3. Amino acids are
released and bonded
together to make a
protein.