Ribonucleic Acid (RNA) &
Protein Synthesis
Ms. Napolitano & Mrs. Haas
CP biology
Think About It!
Imagine that we (Ms. Napolitano & Mrs. Haas) are the
best bakers ever, and we made a cookbook of delicious
cookie recipes. You all would like a copy of our famous
chocolate chip cookie recipe, but we only have one
cookbook. So, we decide to loan it out to one student
at a time. The cookbook can be around from person to
person.
1. What are some of the problems with this form of
sharing information?
2. What is a more efficient way of getting the recipe to
each student?
3. What problems can occur during the copying process?
Recall: DNA Structure
AT
CG
Double helix
Genes
Genes – coded DNA instructions that control the
production of proteins within the cell
Part I: RNA Structure
RNA Structure
Long chain of nucleotides
Sugar
Phosphate
Nitrogenous base
Differences between DNA & RNA:
In RNA:
Sugar is ribose (instead of deoxyribose)
2. Single stranded (instead of double stranded)
3. Contains uracil (instead of thymine)
1.
Types of RNA
Messenger RNA (mRNA)
Carries copies of DNA instructions out of the nucleus
Ribosomal RNA (rRNA)
Make up ribosomes
Transfer RNA (tRNA)
Transfers amino acids to the ribosome that are coded in
the mRNA
Part II: Protein Synthesis
Protein Synthesis
How proteins are made
Need instructions from DNA
Made of 2 parts:
Transcription
2. Translation
1.
Transcription
Copying of the DNA sequence
Occurs in the nucleus
Makes a complimentary strand of mRNA
Uses protein RNA Polymerase
Separates DNA strand
Uses 1 strand of DNA as a template to make mRNA
Starts at a promoter – specific sequence of DNA
RNA Editing
DNA contains segments of introns
Not involved in protein coding
Exons code for proteins
Introns are cut out of the mRNA sequence after
transcription
Exons are spliced together
The Genetic Code
The genetic code is read just 3 letters at a time
Codon – 3 consecutive nucleotides that specify for a
single amino acid
Ex: Consider the RNA sequence UCGCACGGU
This would be read UCG-CAC-GGU
3 different codons: UCG, CAC, & GGU
Codons represent different amino acids
UCG= serine
CAC = histidine
GGU = glycine
The Genetic Code
Since 4 different bases, 43 = 64 possible codons
Some amino acids have more than one codon choice
AUG is always a “start” codon
Where protein synthesis begins
3 stop codons (end of protein synthesis):
UGA
2. UAA
3. UAG
1.
Codon Wheel
Codon Chart
Translation
Recall: During transcription, mRNA code was made
from DNA, mRNA proofread (introns cut out)
Translation – decoding of mRNA to produce proteins
mRNA moves from the nucleus to the ribosomes
Steps of Translation
1. mRNA attaches to the ribosome.
2. As each codon moves through the ribosome, the
proper amino acid is brought in by tRNA.
•
•
Each tRNA carries only 1 type of amino acid
tRNA has 3 unpaired bases (anticodon) that is
complementary to mRNA codons
3. Peptide bonds form between amino acids & tRNA is
released.
4. Polypeptide chain grows until a stop codon is reached.
Translation
Example of Protein Synthesis
DNA strand: TAACGAGGTACT
Transcription (nucleus): mRNA formed by base pairing
mRNA strand: AUUGCUCCAUGA
Translation: mRNA moves to ribosome, read as codons
AUU-GCU-CCA-UGA
Using codon chart, find amino acids that match
Isoleucine-Alanine-Proline-Stop
this is our new protein!
Part III: Mutations
Mutations
Mutations – changes in genetic material
Point mutations – occur at a single DNA point
Substitutions
Frameshift mutations – shift the reading frame of the
genetic message
Dangerous! Could change every following amino acid
Insertions
Deletions
Substitution
Point mutation
One base is changed to a different base
May/may not affect the protein code
Insertions
Frameshift mutation
An extra base pair is (or extra base pairs are) added
Deletions
Frameshift mutation
A base pair is (or base pairs are) removed
Chromosomal Mutations
Chromosomal mutations – changes in the number or
structure of chromosomes
Types:
Deletion – loss of part of a chromosome
Duplication – extra copies of part of a chromosome
Inversion – reverses the direction of part of the chromosome
Translocation – part of the chromosome breaks off &
attaches to another
Chromosomal Mutations
Significance of Mutations
Most mutations do not have an effect on gene expression
Can be very harmful or fatal
Cystic fibrosis
Sickle cell anemia
Cancer
Source of genetic variability
Resistance to HIV
Polyploidy – extra sets of chromosomes
Beneficial in plants – larger and stronger than diploid plants