Download E1-3 NotesProtein Synth

Chapter #12
Nucleic Acids and Protein Synthesis E1-3
I.
DNA –
A. General Facts
1. DNA stores and transmits genetic information
2. DNA tells cells which proteins to make
3. DNA tells cells when to make proteins
4. Proteins form structural units of cells
5. Proteins control chemical reactions in cells
B. DNA Structure
1. Made of repeating subunits called nucleotides
2. Each DNA made of 2 long chains of nucleotides
3. Nucleotide – 3 parts
a. sugar called deoxyribose
b. phosphate group
c. nitrogen base
4. Sugar and phosphate group identical in all DNA
5. Nitrogen base has 4 different kinds
a. adenine (A)
b. guanine (G)
c. cytosine (C)
d. thymine (T)
6. DNA – double helix (like a spiral staircase)
a. discovered by Watson and Crick
7. Covalent bonds B/T sugar and phosphate
8. Nitrogen bases connect to sugar-phosphate backbone
9. 2 Nitrogen bases attach in the middle
a. cytosine always pairs with guanine
b. adenine always pairs with thymine
c. all are connected with hydrogen bonds
C. DNA Replication
1. Replication – copying
2. During replication, 2 nucleotide chains separate by unwinding
3. chains are broken by enzymes
4. nucleotides in cell connect to base pairs (C to G) and (A to T)
5. When 2 new chains created, cell ready for division
D. Accuracy and Repair
1. DNA replication usually very accurate
2. Even one minor error = mutation
3. Number of errors decreases due to repair by enzymes
4. DNA continues to have errors due to carcinogens and simple
errors.
II.
RNA
A. Structure
1. Made of repeating nucleotides
2. Sugar is ribose (instead of deoxyribose)
3. No thymine in RNA
4. Instead, RNA uses uracil in place of thymine for the nitrogen
base.
5. Uracil pairs with adenine
B. Types of RNA
1. 3 different kinds with different functions
a. Messenger RNA (mRNA) – simple chain that carries genetic
info from DNA in nucleus to cytosol.
b. Transfer RNA (tRNA) – single chain that binds to specific
amino acids
c. Ribosomal RNA (rRNA) – most abundant form. Makes up
ribosomes.
C. Transcription –
1. RNA carries genetic info from DNA in nucleus to cytosol to
make proteins.
2. Transcription – where genetic info copies from DNA to RNA
3. Steps –
a. RNA binds to regions of DNA that make a single gene (in
eukaryotes)
b. Nitrogen bases pair up (Uracil with adenine/ guanine with
cytosine)
c. Single strand made until single gene copied
D. Products of Transcription
1. Makes the 3 different kinds of RNA
2. mRNA moves into cytosol to make proteins
III.
Protein Synthesis
A. Protein Composition
1. Made of amino acids (20 different kinds amino acids)
2. Sequence of amino acids determines the proteins shape.
3. The shape determines how protein will bind with other molecules
B. Genetic Code
1. mRNA’s sequence of nucleotides correlates to specific amino
acids.
2. Genetic Code – correlation B/T nucleotides and amino acids
3. Codon –
a. 3 mRNA nucleotides
b. Codes for specific amino acid
c. Some codons do not code for amino acids, but instead mark the
end of a segment
C. Translation
1. Starts when mRNA leaves the nucleus
2. mRNA moves to a ribosome
3. tRNA transports amino acids to ribosomes
4. tRNA has 3 nucleotide sequence called anticodon
5. tRNA anticodon binds to mRNA codon
6. amino acids slowly added in order to make specific protein
D. Ribosomes –
1. made of rRNA and proteins
2. Free ribosomes – make protein for cell
3. Rough ER ribosomes – make protein for export
4. Ribosomes bind to mRNA and tRNA
5. Protein assembly occurs in ribosomes
E. Codons
1. Codons – 3 Nitrogen bases (UUU, CUA, etc.)
2. Several codons can make the same amino acid
(UUA, UUG, CUC = amino acid leucine)
3. Some codons stand for “start” or “stop” (mRNA translation
stops or begins).
F. Protein Synthesis
1. mRNA leaves nucleus/travels to ribosome
2. tRNA picks up amino acids in cytosol and delivers to mRNA
codons
3. Once a ribosome reaches a “stop” codon, it releases mRNA