Protein Synthesis
Modern Genetics: Protein Synthesis
DNA:
 Deoxyribose Nucleic Acid (from the
nucleus)
 Discovered by Watson and Crick
 Genetic material replicates or doubles
(during mitosis or meiosis)
 The process where genetic info is passed
from generation to generation
 Controls cell activities through
enzymesprotein
 Provides codes or instructions for making
proteins
1. Structure of DNA
 Twisted ladder made of
nucleotides
 Phosphate
 Sugar – 5 carbon
Deoxyribose - DNA
 nitrogen base
 Nitrogen Bases are:
1. Purines – double carbon ring
a. Adenine
b. Guanine
2. Pyrimidines – single carbon ring
a. Thymine
b. Cytosine
 Complimentary Base Paring between bases: Base pairing rule
1. Adenine to Thymine (RNA has Uracil not Thymine)
2. Guanine to Cytosine
3. Base pairs are bonded together by weak hydrogen bonds
2. DNA replication
 DNA separates b/w nitrogen bases
 Hydrogen bonds are broken
 Each strand becomes a “template” where replication occurs
 DNA replication results in two exact copies of the cells DNA
1 is the original DNA strand the other is a new strand
 Provides information to RNA for protein synthesis
RNA
 Necessary for protein synthesis (proteins act
as enzymes which regulate the body
 Ribonucleic acid is different from DNA in
3 ways
1. RNA is Single stranded
2. RNA contains ribose not Deoxyribose
3. Instead of Thymine RNA uses Uracil
to pair with Adenine
1. RNA Transcription
 “reading” the code
on a gene to create
a strand of RNA
 “start” signal or the
promoter signal on
the gene begins the
process of
transcription
 RNA polymerase
unwinds a section
of the double helix
 RNA floating in the nucleus binds to the exposed base pairs on the strand
of DNA.
 At the “stop signal, or terminal signal, the sequence of RNA is complete
 Transcription results in a new molecule/strand of RNA called messenger
RNA or mRNA
2. Messenger RNA:
 Made in the nucleus from DNA
 Carries instructions for making proteins to ribosomes (site of protein
synthesis)
 Ribosome “read” the mRNA
 Instructions on the mRNA are written as a 3 nucleotide sequence CGU
 This sequence is called a CODON
 The codon (3 nucleotide sequence) codes for a specific amino acid, or
signals to start ( begins at AUG of the mRNA) the translation process or
stop the process (UAA, UAG, UGA)
3. Transfer RNA:
o tRNA (from the cytoplasm) carries an amino
acid on one end and has an anticodon on the
opposite end
o Anticodon – 3 nucleotide sequence that is
complimentary to the codon on the mRNA
o The complimentary tRNA binds to the mRNA
(at the ribosome) and an amino acid is bonded
to an adjacent a.a. with a peptide bond.
o The process is repeated creating a chain of amino acids
o the chain of a.a builds a specific protein
The process of reading the mRNA to assemble amino acids into
proteins is called: Translation.
Codons code for the following Amino Acids. The chain of a.a represent a specific
protein.
The whole process looks something like this:
DNA  transcription RNA translation  amino acids protein
One more Thing….
 During transcription:
 Transcribed genes produce: INTRONS and EXONS on the strand of RNA
 Introns- DO NOT CODE FOR AMINO ACIDS (proteins)
 Exons- codes for the amino acids (proteins)
 As RNA is being made, transcription, introns are “taken out” and left in the
nucleus later stored in the nucleolus.
 Exons are joined together to form a complete functional strand of RNA, which
then leave the nucleus now called mRNA