Transcript Protein Synthesis

What’s the central dogma of biology?
A.
B.
C.
D.
DNA  RNA  Protein
DNA  Protein  Gene
DNA  Keratin  Hair
DNA  RNA  Amino Acid
What’s the 1st step of protein synthesis?
A.
B.
C.
D.
Protein
Transcription
Translation
DNA
Where does transcription take place in the cell?
A.
B.
C.
D.
Cytoplasm
Ribosome
Nucleus
Cell Membrane
From Gene to Protein
• Genes are DNA sequences that hold
the instructions to build a protein.
– For example, there’s a gene that
codes for a protein called keratin.
Keratin is the protein that
makes our hair & nails.
Protein Synthesis
DNA  RNA  Protein
• Protein synthesis (making
proteins from your genes)
occurs in 2 steps:
– Transcription
– Translation
Where we left off…
• We’ve completed the 1st step of protein
synthesis (transcription)… now what?
TRANSLATION
• We’ve created an mRNA copy of the gene.
• The mRNA has left the nucleus & is
headed to the cytoplasm.
Protein Synthesis Translation
Translation
• The mRNA made during
transcription is used to
make a protein.
– DNA  mRNA  Protein
Remember!
• Proteins (sometimes called polypeptides) are
macromolecules made of monomers called amino acids.
So, to build a protein, we need
to link together amino acids.
Translation – Step 1
• The mRNA molecule (made during transcription)
attaches to a ribosome in the cytoplasm.
Translation – Step 2
• The mRNA is broken down into
sets of 3 nucleotides, or codons.
• The nucleotides are read in
“words” made of 3 nucleotide
“letters”.
• Each “word” is called a codon &
contains the genetic code for 1
amino acid.
Each codon on an mRNA sequence codes for a
specific amino acid.
Translation – Step 3
• As each codon of the mRNA moves through the ribosome,
the correct amino acid is brought to the ribosome by tRNA.
• Each tRNA molecule has a group of 3 nucleotides
called the anticodon & an amino acid attached.
– The anticodons pair with the codons.
In order for the tRNA to attach the amino acid, it needs to
bind to the mRNA sequence using its anticodon.
The anticodon is complementary to the codon!
The first “word”, or start codon, is
always the same for every
protein. It is always AUG.
Using the genetic code wheel, you can figure out which
amino acid a codon represents. Which amino acid is
associated with the start codon AUG?
Methionine
Move from the inside out!
There are a total of 20 different amino acids that can be
arranged in different ways to make different proteins.
Translation – Step 4
• The ribosome transfers the
amino acid from the tRNA to
the polypeptide chain being
formed in a process called
elongation.
– This forms a peptide bond
between the amino acids,
which is why proteins are
called polypeptides.
Translation – Step 5
• The empty tRNA molecule exits the ribosome & is
recycled by the cell & can bind another amino acid.
Translation – Step 6
• The ribosome continues to match codons in the mRNA
with anticodons in tRNA until it reads a codon that says
“stop.” When this happens, the ribosome releases the
mRNA & the protein.
Could you give me the amino acid sequence of this gene?
1. DNA
2. Make mRNA
3. Separate mRNA
into codons
4. Use codon chart to
find amino acids
CACGTAGACTGAGGACTC
GUGCAUCUGACUCCUGAG
GUG-CAU-CUG-ACU-CCU-GAG
Val-His-Leu-Thr-Pro-Glu