1. Cell Structure
Cell = 80% protein
Cell
membrane
2. Many Cell Processes are based on Proteins…
Like Hormones (signals)
Enzymes (speed up reactions)
Membrane Channels (transport materials), and
Neurotransmitters(carry nerve / brain messages)
Protein Structure:
• Large molecules made up of thousands of amino acids
• The properties of the molecules are determined by:
•
•
•
The type of the amino acids included
The number of the amino acids used
The order in which the amino acids are joined
Protein Functions:
As catalysts (enzymes)
As building materials (muscles)
…And much, much more!
As antibodies
As hormones
Nucleic acids made up of chains of nucleotides
Nucleotides consist of:
A base
A sugar (ribose)
A phosphate
Two types of nucleic acids in cells:
Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)
Two main differences:
1.
Deoxyribonucleic acid (DNA) – “Double Helix”
Ribonucleic acid (RNA) – “Single Strand”
2. Different Nucleotides
•
•
Thymine in DNA
Uracil in RNA
Let’s think of Protein Synthesis like a Recipe…Such as Baking a Cake!!
What is need for Protein Synthesis is like a Recipe’s Ingredients: (Instead of flour, sugar,
eggs, etc., for a cake…
1.
2.
DNA (Deoxyribonucleic acid)
RNA (Ribonucleic acid)
We will need three kinds (mRNA, tRNA, and rRNA)
Messenger RNA (mRNA) - carries genetic information from DNA in nucleus to cytoplasm
where proteins synthesized
Transfer RNA (tRNA) - carries amino acids from amino acid pool to mRNA
Ribosomal RNA (rRNA) - joins with ribosomal proteins in ribosome where amino acids
joined to form protein primary structure.
3.
4.
Ribosomes
Amino Acids
We will need 20 kinds (since there are 20 different amino acids)
Now lets start “cookin’!” Following the analogy of a recipe…Here are
the directions: (two main steps—like mixing dry ingredients and
mixing other ingredients)
Transcription - information transcribed from DNA into mRNA.
Transcription (writing the “message”)
DNA ►mRNA
Translation - information in mRNA translated into a protein.
Translation (reading the “message”)
mRNA ►tRNA►protein (AA chain)
Codon is 3 bases long
Information transcribed from
DNA into RNA
Location = nucleus
Steps:
1. The part of the DNA molecule (the gene) that the cell wants the information
from to make a protein unwinds to expose the bases.
2. Enzyme binds to DNA, unzips it.
The mRNA copy is made with the help of RNA polymerase.
This enzyme joins up the mRNA nucleotides to make a mRNA strand.
3. This mRNA strand is a complementary copy of the DNA (gene)
Free mRNA nucleotides in the nucleus base pair with one strand of the unwound DNA molecule.
mRNA copy of gene made from DNA template*U replaces T in RNA
4. The mRNA molecule leaves the nucleus via a nuclear pore into the cytoplasm
5. The mRNA moves to ribosome and DNA helix rewinds
Information Translated from mRNA ►tRNA►protein (Amino
Acid chain)
Location = cytoplasm (1st) then ribosome (2nd)
(NOTE: first codon in mRNA is the start codon AUG)
Information in mRNA translated into primary sequence of a protein in
4 steps:
ACTIVATION
INITIATION
ELONGATION
TERMINATION
(Animation on teacherworld.com)
Information in mRNA translated into primary sequence of a protein in 4 steps:
ACTIVATION
INITIATION
ELONGATION
TERMINATION
ACTIVATION
1.
tRNA molecules are activated as tRNA synthetase enzyme attaches their
complementary amino acids to them.
Information in mRNA translated into primary sequence of a protein in 4 steps:
ACTIVATION
INITIATION
ELONGATION
TERMINATION
INITIATION
1.
mRNA copy attaches to the small subunit of the ribosome in cytoplasm. 6 of the bases in
the mRNA are exposed in the ribosome.
2.
tRNA anticodon UAC bringsAA (methionine)to mRNA codon
on ribosome
3. Initiator tRNA attaches to start codonA tRNA bonds complementarily with the mRNA via
its anticodon.
4.
Larger body of ribosome combines with smaller body.
Information in mRNA translated into primary sequence of a protein in 4 steps:
ACTIVATION
INITIATION
ELONGATION
TERMINATION
ELONGATION
1. A second tRNA bonds with the next three bases of the mRNA, the amino acid links onto
the amino acid of the first tRNA via a peptide bond.
(Reminder) Each tRNA specific for one amino acid only, but some amino acids coded for by up
to 6 codons.
Order of bases in mRNA codons determine which tRNA anticodons will align and
therefore determines order of amino acids in protein
2. The ribosome moves along one codon (3 bases long). (The first tRNA leaves the
ribosome.)
3. A third tRNA brings a third amino acid.
4. Ribosome moves down mRNA to next codon
5. tRNA anticodon brings & attaches next AA with peptide bond.
Information in mRNA translated into primary sequence of a protein in 4 steps:
ACTIVATION
INITIATION
ELONGATION
TERMINATION
TERMINATION
1. Eventually a stop codon is reached on the mRNA This final codon on mRNA
contains termination signal
2. Releasing factors cleave polypeptide chain from tRNA that carried final amino
acid. The newly synthesised polypeptide leaves the ribosome.
3. mRNA is released from ribosome and broken down into nucleotides.
• Protein synthesis is an essential part of our body!
• Proteins are long chains of amino acids which serve many
roles, from enzymes, to the basic structural unit of our cells.
• Protein synthesis involves not only amino acids, but nucleic
acids and ribosomes as well.
• Protein synthesis can be likened to a recipe, with ingredients
and directions for preparing the “protein cake”!
Making a Recipe Card for Protein Synthesis
Use your notes and the 4 by 6 index card I gave to you
to write your own “recipe card”.
Recipe Name
Ingredient List
Directions
1.
2.
1.
2.
3.
http://staffweb.psdschools.org/shunter/Bioweb/DN
A%20Protein%20Synth/Protein%20Synthesis.pdf
www.worldofteaching.com/powerpoints/biology/prot
ein%20synthesis.ppt
www.unisanet.unisa.edu.au/.../Lecture%20Presentat
ion%20-%20Protein%20Synthesis.ppt