Protein Synthesis-How do we go
from genotype to phenotype
RNA
• There are three differences between RNA and DNA:
– RNA is single stranded, DNA is double stranded
– RNA contains uracil and not thymine, DNA
contains thymine not uracil
– RNA has ribose as its sugar, DNA has
deoxyribose
• There are three types of RNA:
– Messenger RNA (mRNA)-is made by
copying the DNA
• DNA can’t leave the nucleus
• Takes strand message to ribosomes
– Transfer RNA (tRNA)-carries the correct
amino acid to the ribosome from the
cytoplasm
– Ribosomal RNA (rRNA)-makes up the
ribosome
Protein syntheis
• The DNA of a person contains about 50,000
genes each of which codes for the making of a
protein.
• Hair and hemoglobin are proteins that your
body makes. Enzymes are also proteins.
• Everything in your body is based on the
making of proteins!
Transcription
• The first phase of protein synthesis is
transcription which takes place in the nucleus.
• This is the process of copying DNA into
mRNA.
• It allows the code that is on DNA to be copied
and taken to the ribosome via mRNA.
Steps of Transcription
• RNA polymerase will initiate the
making of mRNA in the same way that
DNA polymerase replicates DNA. We
call this the start codon.
• A codon is a set of three bases and all
RNA is divided up in sets of three.
• The transcription continues until the
stop codon is reached. Then, the
polymerase releases the DNA and the
newly synthesized RNA strand.
TRANSCRIBE THESE ON
YOUR NOTEGUIDE.
• ATCAT TCGGGAT
UAGUAAGCCCUA
• CCATTACGGGA
GGUAAUGCCCU
SPLICING
Before the mRNA can go to the ribosome, it
needs to be spliced.
– The junk (parts of the DNA that are noncoding
regions) called introns need to be cut out.
– Exons (coding regions) are then stuck together.
This is the correct concise message.
Translation
• The second part of protein synthesis takes
place at the ribosome.
• The mRNA that was made in transcription
travels out of the nucleus and to a ribosome on
the ER or in the cytoplasm.
• Amino acids that are freely floating in
the cytoplasm are transported to the
ribosome by the tRNAs.
• Part of the tRNA contains a region of
three bases called the anticodon.
– The anticodon will match with the mRNA
complementary codon.
– THE ANTICODON DOES NOT TELL
WHAT AMINO ACID IS ATTACHED TO IT.
Making a protein
• The mRNA attaches to one of three binding sites on
the ribosome.
• As the ribosome moves along the mRNA, each
mRNA codon is paired with the correct tRNA
anticodon.
• The pairing of the next amino acid creates a bond
between the two amino acids called a peptide bond.
• In this way, the entire mRNA molecule is read,
making an increasingly long chain of amino acids all
bonded to one another, until a stop codon is reached.
Watch the animation.
http://www.wisconline.com/objects/index.asp?objID=AP1302
Finishing protein synthesis
• Protein synthesis stops when it hits the stop codon
• The chain of amino acids will be released and fold
into its unique shape. This usually happens at the
ER or the GA.
• The order of amino acids dictates the shape of the
protein. The shape determines the function of the
protein.
• http://www.lewport.com/10712041113402793/lib/10712041113402
793/Animations/Protein%20Synthesis%20%20long.
swf
Write the anticodons for the
codons
• AUGCAUUAGGCCAU
UACGUAAUCCGGUA
• CGAAUACAGGAU
GCUUAUGUCCUA
Write the amino acid sequence
from the mRNA sequence.
• AUGCAGCAUUAUACC
Methionine glutamine histidine tyrosine threonine
• CGAAUACAGGAU
Arginine isoleucine glutamine aspartic acid