Transcript Athena, Jen and Natalie`s Powerpt

Protein Synthesis
Athena, Jen, Natalie
DNA versus RNA
DNA
RNA
Contains a 5-C sugar
Contains a 5-C sugar
5-C sugar is deoxyribose
5-C sugar is ribose
Each nucleotide has 1 of 4 nitrogenous
bases
Each nucleotide has 1 of 4 nitrogenous
bases
The bases are adenine, thymine, cytosine
and guanine
The bases are adenine, uracil, cytosine
and guanine
Double stranded molecule
Single stranded molecule
Transcription
When a cell needs to make specific polypeptides
Transcription factors tell a special enzyme where to bind
Upstream from a gene, template strand of DNA,
This enzyme is called RNA polymerase
It binds to a site packed with adenine and thymine
It’s not transcribed but unwinding is very easy
Between these bases are only 2 hydrogen bonds;
This promoter region’s bonds are not as strong
RNA polymerase unwinds the Helix
And so the template strand gets complimented
Into a single strand of mRNA,
There’s no thymine in it
But uracil takes its place
Polymerase then adds nucleotides
In the direction of mRNA’s 5 to 3 prime
Just like DNA replication
It’s the direction of all genetic creation
The DNA strand that is read is called the template
Its bases compliment those bases in the RNA
A template strand of TACTG
Will code for AUGAC
But what about the other strand of DNA?
It isn’t read at the same time as the polymerase
Its coding strand and RNA are identical
Except thymine contains the base uracil
Protein synthesis
Protein Synthesis
Begins in the nucleus
mRNA is synthesized
Then to the cytoplasm where it binds
To a ribosome tRNA finds
Amino acids to form a polypeptide
Gene to polypeptide
Transcription happens ‘til a terminator sequence
Where there’s RNA and DNA dissociation
The polymerase then is free to bind
With another promoter that it can find
Before primary transcript leaves the nucleus
It’s been modified because outside of it
It would be destroyed by digestive enzymes
We wouldn’t want that cause the cell would probably die
The 5 prime cap, 7- methylguanosine
Is added to the 5 prime end of our primary
Transcript, and then a poly-A tail
Is added to the 3 prime end so it won’t fail
There are parts of our molecule that do not code
For a polypeptide, and so...
For our protein not to be dysfunctional
Introns are cut out by spliceosomes
Introns versus exons
• Introns: DNA or RNA segments that interrupt
the sequence of genes
• Exons: DNA or RNA segments with important
info coding for a protein or peptide sequence
Prokaryotes versus Eukaryotes
• Eukaryotes have many more genes, spread
across multiple chromosomes
• Prokaryotes have fewer genes all located on
one chromosome
Where do we go next?
• Then out to the cytoplasm mRNA goes
• Where it meets up with its friend ribosome
• 60 and 40S subunits then clamp on to the
mRNA...
Next up: Translation!
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In the ribosome there are 2 special sites
A is for acceptor P is for peptide
Once the subunits have clamped on
mRNA reading frame is read in codons
Codon: a sequence of 3 nucleotides
AUG: the first codon recognized
The start codon codes for methionine
Whose tRNA enters the P-site
tRNA: single stranded nucleic acid
It’s shaped like a clover and here’s what happens
Aminoacyl tRNA synthetase
Binds one amino acid to the tRNA
tRNA also has an anticodon
This complements the mRNA codon
If the codon transcribed was AUG
The anticodon would be UAC
Methionine tRNA is in the P site
A second tRNA enters the A site
The 2 amino acids then peptide bind
To begin the formation of a polypeptide
The first transfer RNA leaves the ribosome
The second one moves over for elongation
To the A site another one comes along
And it goes on and on and on and on
Until comes the end of translation
When the A site hits a stop codon
For these codons no tRNA exist
Elongation is almost finished
A release factor protein dismantles the complex
The ribosome can bind to more mRNA next
Sugars or phosphates may be added at this time
And these polypeptides make up proteins and enzymes
Roles of proteins in life
1. Proteins in the cell have a duty as enzymes,
which catalyze chemical reactions
2. Proteins are necessary in animals' diets, since
proteins are crucial in the formation of amino
acids. Without proteins they would not have
the nutrients they need to survive. They
obtain essential amino acids from food.
Primary Protein Structure
The amino acid sequence, determined by the
base sequence of the gene that codes for the
protein
Secondary Protein Structure
Secondary structures have cylindrical alpha
helices and planar beta pleated sheets, which
form due to H-bonds between the peptide
groups of the main chain
Tertiary Protein Structure
3D conformation occurs
because of protein folding,
which is stabilized by Hbonds, hydrophobic
interactions, ionic bonds &
disulphide bridges. The
bonds are intramolecular,
and form between the R
groups of different amino
acids.
Quaternary Protein Structure
• 2 or more polypeptide
chains associate to form a
single protein
• Ex. Haemoglobin consists
of 4 polypeptide chains.
Haem group is a prosthetic
group
• Conjugated proteins have a
non-polypeptide structure
called a prosthetic group
Gene Mutations & their impact
• Addition/deletion of nucleotides  a shift in
the reading frame of the codons in the mRNA.
This may alter the amino acid sequence during
translation. This can alter the function of the
protein.
• Base Pair substitution: replacement
or substitution of a single nucleotide base
with another in a DNA/RNA molecule.
Impact of gene mutations
• A condition caused by mutations in one or
more genes is called a genetic disorder.
• What are some examples of genetic disorders?
Credits
• Kathleen June, singer songwriter who wrote
the protein synthesis song
• IB Biology textbook
• Biology 12 textbook