PROTEIN SYNTHESIS

Question 1

Proteins are vital to cell functions, such as:

Answer 1

1. Enzymes.
2. Receptors.
3. Cellular structure – cytoskeleton.
4. Transportation across the membrane.
5. Cellular movements – cilia and flagella.
6. Hormones and signals.
7. Antibodies in immune response.

Question 2

Proteins synthesis is

Answer 2

the process where the cell creates polypeptides. 𝐷𝑁𝐴 is transcribed into 𝑚𝑅𝑁𝐴 which is then translated into a chain of amino acids.

Question 3

There are two steps of proteins synthesis:

Answer 3

1. Transcription.

2. Translation.

Question 4

RNA

Answer 4

𝑅𝑁𝐴 copies 𝐷𝑁𝐴 information and transfers it to site of protein synthesis (ribosomes) and translates it into proteins found in both the nucleus and the cytoplasm. 𝑅𝑁𝐴 take part in transcription and translation. Exists
as a single strand. Its base pairs are adenine to uracil (2 hydrogen bonds) and guanine to cytosine. It has
oxygen on carbon number 3 of the base.

Question 5

Types of 𝑅𝑁𝐴

Answer 5

• 𝑚𝑅𝑁𝐴 (messenger) – transports 𝐷𝑁𝐴 information from the nucleus to the cytoplasm.
• 𝑟𝑅𝑁𝐴 (ribosomal) – composes the ribosomes, the site of protein synthesis.
• 𝑡𝑅𝑁𝐴 (transport) – translates the nucleic acids language to amino acids.
• 𝑆𝑛𝑅𝑁𝐴 (small nuclear) – small nucleic 𝑅𝑁𝐴. They regulate modification: taking off introns and
  maintaining telomeres.

Question 6

Transcription is

Answer 6

𝐷𝑁𝐴 is copied into 𝑚𝑅𝑁𝐴 by the enzyme called 𝑅𝑁𝐴 polymerase encodes for protein’s copy. It occurs in
the nucleus in a eukaryotic cells and in the cytoplasm of prokaryotic cells.

Question 7

Process of Transcription:

Answer 7

1. Helicase enzyme unwinds the 𝐷𝑁𝐴 to expose a promotor and the gene segment.
2. 𝑅𝑁𝐴 polymerase binds to a 𝐷𝑁𝐴 strand. Only one strand serves as a templet.
3. 𝑅𝑁𝐴 polymerase synthesizes a complementary strand, pre-𝑚𝑅𝑁𝐴/𝐻𝑛𝑅𝑁𝐴 (𝑚𝑅𝑁𝐴 before modification) in a direction from 5 to 3 according to the 𝐷𝑁𝐴 bases.

Question 8

Post transcription modification (pre-𝑚𝑅𝑁𝐴 to mature-𝑚𝑅𝑁𝐴)

Answer 8

1. Capping – 5-guanine cap is added to protect the five-end of the 𝑚𝑅𝑁𝐴 (bonded by a tri phosphide
   bond) . This prevents degradation. Highly regulated and vital to creating a mature and stable 𝑚𝑅𝑁𝐴, so it can undergo translation. There is no capping the transcription happening in the
   mitochondria.
2. Tailing (polyadenylation)– poliy adenine trail is added to protect the three-end of 𝑚𝑅𝑁𝐴 (bonded
   by a one phosphates bond). Polyadenylation is adding of multiple adenines that stretches out the 𝑚𝑅𝑁𝐴.
3. Splicing – editing the 𝑚𝑅𝑁𝐴 by removing introns (non-coded regions) and keeping exon (coding regions/expressed genes) this process is made by 𝑆𝑛𝑅𝑁𝐴.

Question 9

Genetic Language

Answer 9

The genetic language: 𝐷𝑁𝐴 and 𝑅𝑁𝐴 have similar language that is made up of four letters (𝑛 bases). Proteins have a different language that is made of twenty words (amino acids). The letters of 𝐷𝑁𝐴 and 𝑅𝑁𝐴 helps build up the words.

Question 10

A codon

Answer 10

A triplet of three letters is called a codon. A codon is a sequence of three 𝐷𝑁𝐴 or 𝑅𝑁𝐴 nucleotides that
corresponds with a specific amino acid during protein synthesis. Three letter will code to one word. With
three letters we can make 64 words, however we only have 20 words; this is known as redundancy – we
have multiple codons that can code for the same amino acid.

Question 11

Translation

Answer 11

A mature 𝑚𝑅𝑁𝐴 leaves the nucleus throw the pores ad travel to the cytoplasm, where it is decoded by a
ribosome. To produce a polypeptide.

Question 12

Tools used by translation:

Answer 12

RNA and tRNA

Question 13

Ribosome

Answer 13

the site of protein synthesis; compose of two sub units that are – made out of proteins and 𝑟𝑅𝑁𝐴:

• Small ribosomal unit (30s). The biding site of 𝑚𝑅𝑁𝐴.
• Large ribosomal unit (50s). The biding site for 𝑡𝑅𝑁𝐴 (𝐴, 𝐸 and 𝑃 sites).

Proteins produced by ribosomes bond to the 𝑅𝐸𝑅 are secreted or exported out of the cell, while proteins produced by free flouting ribosome are used by the cell inside.

Question 14

tRNA

Answer 14

3𝐷 structure that carries and matches the correct amino acid with the its mRNA codon
at the ribosome site.
- 𝑡𝑅𝑁𝐴 matches by using anticodon nucleotide on the 𝑡𝑅𝑁𝐴 that is complementary to
the codon.

• 𝑡𝑅𝑁𝐴 synthase is an enzyme that binds amino acid to the 𝑡𝑅𝑁𝐴 and creates an aminoacyl-𝑡𝑅𝑁𝐴 complex.
• Wobble position – the last position of the 𝑡𝑅𝑁𝐴 anticodon can exhibit a wobble and thereby shifting to a different 𝑛 base. Even though it doesn’t follow the base pair rules, the 𝑡𝑅𝑁𝐴 can compensate and provide the specific amino acid.

Question 15

Translation process Is done by 3 stage:

Answer 15

Initiation
Elongation
Termination

Question 16

Initiation stage

Answer 16

The same in eukaryote and prokaryote: 𝑚𝑅𝑁𝐴 binds to the small ribosomal subunit which slides in the 5 to 3 direction. It slides on the 𝑈𝑇𝑅 (untranslated region) until it riches a start codon (5−𝐴𝑈𝐺 −3). Next, 𝑡𝑅𝑁𝐴 (anticodon 5−𝐶𝐴𝑈−3) carrying the amino acid
methionine base pairs with the start codon. Finally, the large ribosomal subunit joins the complex completing the ribosomes. 𝑡𝑅𝑁𝐴 is now on the 𝑃 site of the large ribosomal subunit.

Question 17

Elongation Stage

Answer 17

The complete ribosome continues to slide along the 𝑚𝑅𝑁𝐴 while 𝑡𝑅𝑁𝐴 adds new amino acids to the 𝐴 site. 𝑡𝑅𝑁𝐴 exits through the 𝐸 site, and enzyme called peptidyl transferase transfers amino acid to from 𝑃 site to 𝐴 site where there are bonded to each other
by a peptide bond.

Question 18

Termination Stage

Answer 18

Translation process ends when the ribosome reaches to a stop codon (𝑈𝐺𝐴, 𝑈𝐴𝐴 or 𝑈𝐴𝐺) that doesn’t code for an amino acid. Once the 𝐴 site is on the stop codon, a water molecule enters the complex resulting in termination (all parties disassociate).