3.5 Transcription and Translation

3.5.4
EXPLAIN THE PROCESS OF TRANSLATION, LEADING TO POLYPEPTIDE FORMATION:
There is a "cytoplasmic pool" of amino acids, tRNA takes those amino acids from the pool and transfers it to the ribosomes. The amino acids that are brought to the ribosomes by the tRNA are added to the growing end of a polypeptide chain.

3.5.5
DISCUSS THE RELATIONSHIP BETWEEN ONE GENE AND ONE POLYPEPTIDE:
Nucleotides (DNA) code for the production of amino acids which link together in peptide bonds (Polypeptides) to form proteins. The sequence of bases in a gene codes for the sequence of amino acids in a polypeptide.
EXAMPLE:

external image gene.gif

7.3 Transcription

7.3.1
STATE THAT TRANSCRIPTION IS CARRIED OUT IN A 5' - 3' DIRECTION:
Transcription is carried out in a 5'- 3' direction. Only the template(leading) strand is used for transcription. The reason for this is because the lagging replicates in okazaki fragments, which would slow down the process of transcription and leave room for error and also because RNA is single stranded.
EXAMPLE:


external image moz-screenshot.jpgInitiation:

Initiation
Initiation



Elongation
:
external image 400px-Simple_transcription_elongation1.svg.png
Termination:

external image 400px-Simple_transcription_termination1.svg.png




7.4.1- Explain that each tRNA molecule is recognized by a t RNA-activating enzyme that binds a specific amino acid to the tRNA, using ATP for energy.


The tRNA has three active sites, one for each of the following: one ATP, one tRNA activating enzyme, and one amino acid. The tRNA activating enzyme connects an amino acid to the tRNA for use in protein synthesis. This binding requires an ATP.


7.4.2- Outline the structure of ribosomes, including protein and RNA composition, large and small sub-units, three tRNA binding sites and mRNA binding sites.

Most eukaryotic ribosomes are composed of a large and a small subunit that work together during protein synthesis. The large ribosome is made of three different rRNA molecules and over 45 different protein molecules. The small subunit is composed of one rRNA molecule and around 33 different protein molecules. The ribosome also has three tRNA binding sites referred to as the APE sites. It also has mRNA binding sites which hold the mRNA conveyor belt in place while the ribosome moves over it.


7.4.3- State that translation consists of initiation, elongation, translocation, and termination.

Translation consists of four main stages: initiation, elongation, translocation, and termination.

7.4.4- State that translation occurs in a 5'-3' direction.

The ribosome travels along the mRNA strand towards the 3' end from the 5' end. The start codon is nearer to the 5' end indicating that the ribosome starts there and travels to the stop codon which is near to the 3' end of the mRNA strand.


7.4.5- Draw and label a diagram showing the structure of a peptide bond between two amino acids.

Amino acids are connected during protein synthesis to form proteins. The amino acids are binded with peptide bonds between each amino acid. Hence, polypeptide chains get their name from the many peptide bonds holding their amino acids together.


external image peptide_bond.jpg































7.4.6- Explain the process of translation, including ribosomes, polysomes, start codons, and stop codons.


The ribosome binds to the mRNA at the start codon that is recognized only by the initiator tRNA. The ribosome proceeds to the elongation phase of protein synthesis. During this stage, complexes, composed of an amino acid linked to tRNA, sequentially bind to the appropriate codon in mRNA by forming complementary base pairs with the tRNA anticodon. The ribosome moves from codon to codon along the mRNA. Amino acids are added one by one, translated into polypeptide sequences dictated by DNA and represented by mRNA. At the end, a release factor binds to the stop codon, terminating translation and releasing the complete polypeptide from the ribosome.

7.4.7- State that free ribosomes synthesize proteins for use primarily within the cell, and that bound ribosomes synthesize proteins for secretion or for lysosomes.

Free ribosomes synthesize proteins for use within the cell because they can move freely throughout the cell and therefore can go where proteins are needed. Ribosomes that are bound to the endoplasmic reticulum make proteins for within the cell because they are stationary.



DONE