Transcript What we did this week:

What we did this week so far:
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DNA vs. RNA
Transcription
The genetic code
Translation (Protein Synthesis)
DNA vs. RNA
• What is RNA?
▫ Ribonucleic Acid: a copy of DNA that goes out to
the cytoplasm to tell the cell what to do in order to
stay alive!
• How many strands does DNA have?
▫2
• How many strands does RNA have?
▫1
DNA vs. RNA
• DNA –
• Deoxyribonucleic acid
• RNA –
• Ribonucleic acid
DNA vs. RNA
• DNA has a deoxyribose sugar…
but RNA has a…
• The 4 bases for RNA are:
▫ RIBOSE SUGAR!!!
• The 4 bases for DNA are:
▫
▫
▫
▫
*Thymine (T)
Adenine (A)
Guanine (G)
Cytosine (C)
▫
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▫
*Uracil (U)
Adenine (A)
Guanine (G)
Cytosine (C)
Transcription
• are segments of DNA that are templates to
produce RNA molecules
▫ For example:
ATG (DNA)  UAC (RNA)
• Location:
▫ in the nucleus, because it can be destroyed in the
cytoplasm!
Transcription
Transcription
• RNA is made from 1 gene in DNA
• mRNA or Messenger RNA:
▫ sends a message from DNA to the cytoplasm that
codes for a protein
• RNA polymerase: joins the bases together, unzips
the strand, and only begins at the promoter region
• It stops when a new RNA molecule is completed
Promoter
• a DNA segment that allows a gene to be
transcribed
• Helps RNA polymerase where to find where a
gene starts.
• An operator is a DNA segment that turns a
gene “on or off”
• Interacts with proteins to speed up or block
transcription
The RNA editors
• Exons
▫ RNA sequences in the primary transcript that are
found in the mRNA
• Introns
▫ RNA sequences between exons that are removed
by splicing
Introns and Exons
The Genetic Code
• Code that matches codons in mRNA to amino acids
on the tRNA
• Polypeptides: long chain of amino acids connected
to each other
• Start codon?
▫ AUG - methionine
• Stop codons?
▫ UAA, UAG, and UGA
Translation
• Process that coverts or “translates” an mRNA
message into a polypeptide (amino acid)
• One or more polypeptides make up a protein
• The process consists of 4 steps…3 of which
repeats…
Translation process…
• 1) mRNA leaves the nucleus  cytoplasm
• 2) mRNA attaches to the ribosome where the
mRNA codon pairs with the tRNA anticodon
▫ “AUG” is the start codon!
Translation process…
Translation process…
• 3) the ribosome forms a peptide bond between
the first two amino acids and the tRNA detaches
Translation process…
• 4) the ribosome pulls the mRNA strand and then
everything is shifted to the next 3 codons
▫ tRNA leaves and returns to the cytoplasm to be
charged with another amino acid
Translation
ribosome
Polypeptide
chain
tRNA
molecule
mRNA
codon
anticodon
What it looks like!
nucleus
cytoplasm