Protein Synthesis
Definitions
1. Protein Synthesis: the construction of
proteins directed by DNA
---------Consists of 2 steps, which are-----------
2. Transcription: copying DNA in the
nucleus to mRNA
3. Translation: using mRNA as a guide to
form a polypeptide (protein)
What part of the cell cycle?
Mitosis
S Phase
G2 Phase
Definitions
4. rRNA: ribosomal RNA
5. mRNA: messenger RNA
6. tRNA: transfer RNA
Where does protein synthesis happen?
• The ribosomes!
What are the monomers
ribosomes use to build proteins?
• Amino acids
What are proteins used for?
Type of
Function
Enzymes
Example
Function
amylase
Promotes breakdown of
starch
Hormones
insulin
Regulates blood sugar
levels
Structural
keratin
Hair, wool, nails, horns,
hoofs, etc.
Transport
hemoglobin
Carries oxygen in blood
Immune defense
antibodies
Rid the body of foreign
proteins
Contractile
actin
Contracting fibers in
muscles
How does protein synthesis happen?
This is known as the
central dogma
of Biology.
3 Differences between DNA & RNA
DNA:
• Deoxyribose sugar
• Contains thymine (T)
 A-T and C-G
• Double-stranded
RNA:
• Ribose sugar
• Contains uracil (U)
instead of thymine
 A-U and C-G
• Single strand
3 Types of RNA
1. rRNA
a. Location: nucleus and ribosomes
b. Function: combines with proteins to make
ribosomes
3 Types of RNA
2. mRNA
a. Location: nucleus and cytoplasm
b. Function: brings instructions from DNA
in nucleus to ribosomes in the cytoplasm
mRNA
3 Types of RNA
3. tRNA
a. Location: nucleus and cytoplasm
b. Function: brings amino acids to ribosome
to build polypeptides (proteins)
tRNA
How are proteins made?
• Step 1: Transcription – RNA polymerase
splits open DNA and copies it to form a
strand of mRNA. mRNA leaves the
nucleus.
How are proteins made?
• Step 2: Translation – mRNA in the
cytoplasm binds to a ribosome. Ribosome
reads it 3 bases at a time, and matches these
with bases on tRNA attached to an amino
acid. An amino acid chain is formed from
many peptide bonds.
How are proteins made?
• Step 3: Protein folding – polypeptide is
folded, and combined with other
polypeptides to form a protein.
What is a codon?
• mRNA is read 3 bases at a time – a codon is
the 3 base code, or triplet code, of mRNA.
What is a polypeptide?
• A long chain of amino acids linked by
peptide bonds
How many different amino acids
can each codon specify?
• Only one (CUC only codes for leucine)
Can an amino acid have more
than one codon?
• Yes! (ex.: phe, leu, pro, thr, ala, val, gly, etc.)
Transcribe the DNA into mRNA,
then translate it into amino acids.
Animations of Protein Synthesis
http://wwwclass.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.htm
l
http://www.wisc-online.com/objects/index_tj.asp?objID=AP1302
GAME:
http://library.thinkquest.org/20465/g_DNATranscription.html
http://learn.genetics.utah.edu/content/begin/dna/transcribe/