Transcript Transcription, Translation

Transcription,
Translation &
Protein Synthesis
Protein Synthesis
• Protein synthesis - a cell makes
protein based on the message
contained within its DNA.
• However:
– DNA is only found in the nucleus
– Proteins are only made outside the
nucleus – in the cytoplasm.
• RNA – is used to carry these
messages.
Ribonucleic Acids (RNA)
•
There are three types of RNA:
1. mRNA – carries a message from the DNA to the
ribosome
2. tRNA – transports amino acids to the mRNA to
make a protein
3. rRNA – make up ribosomes, which make
protein.
Ribonucleic Acids (RNA)
• RNA is almost exactly like DNA, except:
1. RNA has a sugar ribose
DNA has a sugar deoxyribose
2. RNA contains uracil (U)
DNA has thymine (T)
3. RNA is single-stranded
DNA is double-stranded
Ribonucleic Acids (RNA)
Protein Synthesis
• Occurs in TWO steps:
1.Transcription –information from a strand
of DNA is copied into a strand of mRNA
2.Translation – the mRNA, with the help of
the ribosome, forms a chain of amino
acids (eventually forming a protein)
The Central Dogma
• This order of events is called the
central dogma of molecular biology:
DNA
RNA
P
R
O
T
E
I
N
Step One: Transcription
1. DNA unzips
2. Bases pair up: Free bases in the cell find
their complementary bases along the new
strands. What will be different??
3. New backbone formed: What will be
different??
Step One: Transcription
• Watch this simplified animation:
– Transcription Animation
Step One: Transcription
• Try it! What RNA strand will be made
from the following DNA sequence?
TACGCATGACTAGCAAGTCTAACT
AUGCGUACUGAUCGUUCAGAUUGA
Step Two: Translation
1. Divide the mRNA sequence into
codons.
2. Codons are three-base sections of
mRNA:
AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA
Step Two: Translation
• Watch this simplified animation:
– Translation Animation
Step Two: Translation
2. You need to figure out what amino
acid matches up with each codon:
AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA
?
tRNA
• A go-getter.
• Gets the right amino acids to make the right
protein according to mRNA instructions
• It contains anti-codons
• EX: UAC – mRNA
–
AUG – tRNA
The Genetic Code
Step Two: Translation
2. Since each 3-letter combination
“codes” for an amino acid, you need to
figure out what amino acid matches up
with each codon:
AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA
met
arg
thr
asp
arg
ser
asp
???
Step Two: Translation
2. Since each 3-letter combination
“codes” for an amino acid, you need to
figure out what amino acid matches up
with each codon:
AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA
met
met
thr
asp
arg
ser
asp
STOP
RECAP:
1. DNA is transcribed
into mRNA in the
nucleus.
2. The mRNA leaves the
nucleus and enters the
cytoplasm.
3. The protein is
translated from the
mRNA sequence
using tRNA and amino
acids.