Download Chapter 12.3 and 12.4 RNA and Protein Synthesis The Role of RNA

Chapter 12.3 and 12.4 RNA and Protein Synthesis
The Role of RNA
RNA carries out the instructions and transports the info held in the DNA.
I. General structure of RNA (Ribonucleic Acid)
1. a sugar - in this case the ribose
2. phosphate
3. nitrogen base (A, U, C, G)
II. How does RNA differ from DNA?
THE DIFFERENCES BETWEEN DNA AND RNA
DNA
1. Two strands (double : a thick helix)
2. Has a deoxyribose as a sugar
3. Uses the bases A, T, C, and G
RNA
1. Single stranded
2. Has a ribose as a sugar
3. Uses the bases A, U, C, G
III. Functions of RNA
A. Disposable “copy” of a segment of DNA
B. Most RNA molecules are involved in protein synthesis.
1. Controls assembly of amino acids in protein. **amino acids make up proteins
C. Types of RNA
1. mRNA (messenger) – carries info out of nucleus
2. tRNA (transfer) – transfers amino acids to make up the protein
3. rRNA- (ribosomal) – make up ribosomes (which make protein) **ribosomes are
made in the nucleolus
IV. RNA Synthesis
A. TRANSCRIPTION—The making of RNA molecules from DNA
1. Process:
a. RNA polymerase binds to DNA and separates DNA strands at a promoter (area
with a specific sequence that says “Start here!”)
b. One strand is used as the template to make RNA
c. A similar sequence tells the RNA to “Stop copying here”
B. RNA EDITING
1. RNA requires editing before they are set to go.
2. Large pieces that are removed are called introns – cut out while still IN the nucleus
a. Introns stay IN the nucleus
3. The remaining portions are exons (expressed sequences) are then put back together
to form the final mRNA.
b. Exons exit the nucleus
**What molecules are necessary for transcription?
1) DNA
2) Transcription Factors
3) RNA polymerase
4) ATP
5) Nucleotides
Ribosomes and Protein Synthesis
I. GENETIC CODE
A. Proteins are made from long amino acids in a chain (polypeptide chain)
B. There are 20 different amino acids in the human body.
C. Properties of proteins are in the sequencing of amino acids.
D. Since there are only 4 letters (AUCG)
1. If each letter made an amino acid – we would have 41 = 4 amino acids
2. If two letters made an amino acid – we would have 42 = 16 amino acids
3. If three letters made an amino acid – we would have 43 = 64 amino acids
a. 64 combos are more than enough to cover 20 amino acids
E. Each group of 3 nucleotides is called a codon. Each codon represents a different
amino acid. Each codon specifies a specific amino acid.
F. Example:
mRNA =
UCGCACGGU
Codons =
UCG – CAC – GGU
Amino Acids = Serine – Histidine – Glycine
AUG codon codes for the amino acid Methionine and is the only START codon.
UAA, UAG and UGA are the three and only three STOP codons.
II. TRANSLATION
A. Process:
1. Using the mRNA sequence to make the string of amino acids at the rRNA which is
located in the cytoplasm
2. Ribosomes read the mRNA and put it to use.
3. mRNA attaches to the ribosome
4. The proper amino acid is brought by the tRNA which has an anticodon on the
end of it (opposite sequence to the codon).
5. One part is attached to the next through a peptide bond (first amino acid to
second amino acid)
6. Ribosome breaks the bond that had held it to the tRNA and releases the tRNA.
7. The polypeptide chain continues to grow until the ribosome reaches a stop
codon.
**What molecules are necessary for translation?
1) mRNA
2) Small ribosomal subunit
3) Large ribosomal subunit
4) tRNA—needs an amino acid attached to it.
3 steps of translation
1) Initiation
2) Elongation
3) Termination
GENES AND PROTEINS
Proteins catalyze reactions. Genes code an enzyme to produce proteins that can control for a
given trait. Proteins are the key to almost everything that cells do.
MUTATIONS
I. What are mutations?
A. Mutations are changes in the DNA sequence.
B. Mutations are changes in genetic information
C. Two basic categories of mutations.
1. Gene mutations (in gene sequence)
2. Chromosomal mutations (in whole chromosomes)
D. Gene mutations
1. Point Mutation – single base change in a sequence of DNA
a. Substitution
b. Insertions
c. Deletion
Substitution
Insertion
Deletion
2. Frameshift Mutation – Insertions and/or deletions are also called
frameshift mutations. The addition or deletion of a base shifts the
“reading frame” of genetic message – can alter the entire amino acid
sequence.
E. CHROMOSOME MUTATIONS
1. Deletion – removal of a gene on a chromosome
2. Duplication – addition of a gene on a chromosome
3. Inversion – part of a chromosome is taken out, reversed and put back in
4. Translocation – part of one chromosome breaks off and attaches to a
nonhomologous chromosome
II. Causes of Mutations
A. Can be caused by natural events (inside the body when replication or transcription
occurs) or artificial means.
B. Mutations arise from mutagens which can be chemical or physical agents in the
environment (artificial means)
1. Chemical mutagens
a. Pesticides
b. Plant alkaloids
c. tobacco smoke
d. Environmental pollutant
2. Physical mutagens
a. Electromagnetic radiation
1. X-rays
2. Ultraviolet Light
**Cells can sometimes repair the damage and sometimes they can not.
III. Harmful and Helpful mutations
A. Harmful Effects
1. Cancer
a. Can be genetically pre-disposed or can be brought on by artificial means
2. Sickle cell anemia (point mutationsubstituted one nitrogenous
baseGlutamic acid is produced instead of valine)
a. Genetic
b. Changes shape of your blood cells
c. Can’t carry oxygen in blood very well
d. Symptoms
1. Severe pain
2. Frequent infections
3. Stunted growth
4.**Resistant to malaria
B. Beneficial Effects
1. Increased body strength and density
2. Increase resistance to HIV