Post on 13-Dec-2015
12–3 RNA and Protein Synthesis
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What is RNA?
Ribonucleic acid.. It too like DNA is a nucleic acid!
RNA contains codes for making proteins (body tissues such as muscle, hair, enzymes, etc..)
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Let’s compare RNA to DNA
DNA RNADeoxyribo
seSugar Ribose
A, T, G, C Nitrogenous Bases
A, U, G, C
Double Strands SingleNucleus Location Anywhere
in cell
3 Types of RNA
Messenger mRNA
Ribosomal rRNA
Transfer tRNA
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Messenger RNA (mRNA) Makes a copy of DNA. Every 3 letters on an mRNA is a codon (we will get there, don’t worry )
ribosomal RNA (rRNA) are what ribosomes are made of.
Types of RNA
transfer RNA (tRNA) Carry or “transfer” amino acids to the ribosome.
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The Genetic Code
The genetic code is the “language” of mRNA instructions.
The code is written using four “letters” (the bases: A, U, C, and G).
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The Genetic Code
A codon consists of three consecutive nucleotides on mRNA that specify a particular amino acid.
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For Example…
Consider the following RNA sequence:
UCGCACGGU
This sequence would be read 3 bases at a time as:
UCG-CAC-GGU
The codons represent the different amino acids:
Serine-Histidine-GlycineCopyright Pearson Prentice Hall
Because there are 4 different bases….
There are 64 possible 3-base codons (4 x 4 x 4 = 64).
Look at Figure 12-17 in your book on pg. 303.
This shows all 64 possible codons of the genetic code.
See mRNA Codon/Amino Acid Chart Handout!!!
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Looking at Figure 12-17….
As you can see, some amino acids can be specified by more than one codon.
For example, 6 different codons specify the amino acid Leucine and 6 others specify Arginine.
There is also one codon, AUG, that can either specify methionine or serve as the initiation, or “start” codon for protein synthesis.
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See if you can figure this out…
What amino acid is specified by CAU?
What is the codon for tryptophan?
What are two possible codons for glutamine?
What amino acid is usually the first amino acid of a protein? How do you know?
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Video Time
So… What the heck is
protein synthesis?
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Step 1 of Protein Synthesis
1.Transcription: mRNA is transcribed from DNA in the nucleus and released into the cytoplasm
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Step 2 of Protein Synthesis
2.Translation: mRNA attaches to a ribosome and an amino acid is brought by a tRNA to the mRNA.
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It works like an assembly line
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tRNA
Ribosome
mRNA
Lysine
Translation direction
-The process continues until the ribosome reaches a stop codon.
-It then releases the newly formed polypeptide (which creates a protein) and the mRNA molecule completes the process of translation.
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Polypeptide
Ribosome
tRNA
mRNA
Why do we care about what protein synthesis does?
Proteins determine eye color, hair color, etc...
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RNA Editing
Some DNA within a gene is not needed to produce a protein. These areas are called introns.
The DNA sequences that code for proteins are called exons.
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End Show
- or -Continue to: Click to Launch:
Slide 22 of 39
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12–3
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Slide 23 of 39
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12–3
A base that is present in RNA but NOT in DNA is
a. thymine.
b. uracil.
c. cytosine.
d. adenine.
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Slide 24 of 39
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The nucleic acid responsible for bringing individual amino acids to the ribosome is
a. transfer RNA.
b. DNA.
c. messenger RNA.
d. ribosomal RNA.
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Slide 25 of 39
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A region of a DNA molecule that indicates to an enzyme where to bind to make RNA is the
a. intron.
b. exon.
c. promoter.
d. codon.
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Slide 26 of 39
A codon typically carries sufficient information to specify a(an)
a. single base pair in RNA.
b. single amino acid.
c. entire protein.
d. single base pair in DNA.
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12–3