Biology-genetics-protein synthesis

1. FatmaEhab &
Lojain Ashraf
Protein Synthesis

2. Functions of
protien
TABLE OF CONTENTS
01 02 03
04
Protein
composition
Types of RNA
Transcription
05 06
translation Q&A

3. Uses of Proteins

4. • Proteins are composed of amino acids – there are 20
different amino acids.
• Different proteins are made by combining
these 20 amino acids in different
combinations

5. Three Main Types of RNA
Messenger RNA (mRNA) - Carries copies of instructions
for the assembly of amino acids into proteins from DNA
to the rest of the cell (serve as “messenger”)
Ribosomal RNA (rRNA) – Makes up the major part of
ribosomes, which is where proteins are made.
Transfer RNA (tRNA) - Transfers amino acids to
ribosomes during protein synthesis

6.  DNA → RNA
2 Steps to Make a Protein:
1. Transcription 2. Translation
 RNA → Protein
(Chain of amino
acids)

7. Transcription
01

8. Step 1: Initiation
It occurs when the enzyme RNA polymerase binds
to a region of a gene called the promoter. The
promoter is a specific nucleotide sequence of DNA
where RNA polymerase binds and initiates
transcription. Then the DNA strands unwind and
separate.
Transcription steps

9. Step 2: Elongation
• Elongation is the addition of
nucleotides to the mRNA strand. RNA
polymerase builds the mRNA
molecule, using complementary base
pairs.

10. Step 3: Termination
it is the ending of transcriptionand
occurs when RNA polymerase crosses
a stop (termination) sequence in the
gene. The mRNA strand is complete, and
it detaches from DNA.
The end product of transcription is an RNA transcript
which can form any of the following types of RNA:
mRNA, tRNA, rRNA, and non-coding RNA.

11. ● Transcription = DNA  RNA
● Takes place in the nucleus.
● The purpose of transcription is to make RNA copies of
individual genes that the cell can use.
● Produces mRNA, tRNA, rRNA, and non-coding RNA.
● Template strand: the side of DNA that will be used to create an
mRNA strand
Two enzymes help:
1. Helicase - separates DNA helix
2. RNA polymerase – brings RNA nucleotides over to be synthesized
into mRNA

12. • The genetic code is read three letters at a time, called “codons”
on the mRNA strand.
• Each codon will have a special amino acid that matches it!

13. cytoplasm
Translation takes place in
the cytoplasm.
purpose
The purpose of translation
is to synthesize proteins.
Translation
product
Proteins.

14. Step 1: Initiation
• In initiation, the ribosome assembles around
the mRNA to be read and the first tRNA
(carrying the amino acid methionine, which
matches the start codon, AUG). This setup,
called the initiation complex, is needed in order
for translation to get started.
Translation steps

15. Step 2: Elongation
Elongation is the stage where the amino acid chain gets longer.
In elongation, the mRNA is read one codon at a time, and
the amino acid matching each codon is added to a growing
protein chain.
Each time a new codon is exposed:
• A matching tRNA binds to the codon
• The existing amino acid chain (polypeptide) is linked onto
the amino acid of the tRNA via a chemical reaction
• The mRNA is shifted one codon over in the ribosome,
exposing a new codon for reading.

16. During elongation, tRNAs move
through the A, P, and E sites
of the ribosome, as shown
above. This process repeats
many times as new codons
are read and new amino acids
are added to the chain

17. Step 3: Termination
Polypeptides, like all good things, must eventually come to an end. Translation ends
in a process called termination. Termination happens when a stop codon in the
mRNA (UAA, UAG, or UGA) enters the A site.
Stop codons are recognized by proteins called release factors, which fit neatly into
the P site (though they aren't tRNAs). Release factors mess with the enzyme that
normally forms peptide bonds: they make it add a water molecule to the last
amino acid of the chain. This reaction separates the chain from the tRNA, and
the newly made protein is released.
What next? Luckily, translation "equipment" is very reusable. After the small and
large ribosomal subunits separate from the mRNA and from each other, each
element can (and usually quickly does) take part in another round of translation.

18. Q&A
06

19. A polysome could be best described as:
A.an active site of DNA synthesis.
B.an active site of syprotein synthesis.
C.an active site of lipid nthesis.
D.all of the above.
Answer: Option B

20. Which of the following is not a necessary
component of translation?
A.Anticodon
B.mRNA
C.Ligase
D.Amino acid
Answer: Option C

21. On the ribosome, mRNA binds:
A.between the subunits
B.to the large subunit
C.to the small subunit
D.none of these
Answer: Option C

22. Amino acids are joined together into a protein
chain by which of the following?
A. Transfer RNA
B. DNA polymerase
C. Hydrogen bonds
D. Messenger RNA
Answer: Option A

23. The site of protein synthesis is:
A. Ribosome
B. Nucleus
C. Endoplasmic reticulum
D. Chromosome
Answer option: C

24. The structure in a bacterium that indicates
an active site for protein synthesis is
A. a chromosome.
B. a cell membrane,
C. a flagellum.
D. a polysome.
Answer: Option D

25. Proteins contain ____ different amino
acids, whereas DNA and RNA are
composed of ____ different nucleotides
A. 20,64
B. B. 3,20
C. C. 4,20
D. D. 20,4
Answer: Option D

26. Which of the following is not necessary
for protein synthesis to occur, once
transcription is completed?
A. tRNA
B. Ribosomes
C. mRNA
D. DNA
Answer: Option D

27. Ribosomes select the correct tRNAs
A. then bind to the appropriate mRNA
B. solely on the basis of their anticodons
C. depending on their abundance in the
cytosol
D. with the least abundant anticodons
Answer: Option B

28. The anticodon of tRNA:
A. binds to rRNA
B. binds to an amino acid
C. binds to the Shine Dalgarno sequence
D. binds to an mRNA codon
Correct Answer: B

29. Which site of the tRNA molecule
binds to the mRNA molecule?
A. Anticodon
B. Codon
C. Amino acid
D. 5 prime end
Answer: Option A

30. Which of the following has unusual bases?
A. mRNA
B. B.tRNA
C. rRNA
D.hnRNA
Answer: Option B

31. The first step in translation is:
A. binding of the two ribosomal subunits to each
other
B. binding of mRNA to the two ribosomal subunits
C. binding of tRNA to the small ribosomal subunit
D. binding of mRNA to the small ribosomal subunit
Answer: Option D

32. How many bases of nucleic acid determine
a single amino acid?
A. Four
B. One
C. Two
D. Three
Answer: Option D

33. Which is required for protein
synthesis?
A. tRNA
B. mRNA
C. rRNAD.
All of these Answer: Option D

34. On the ribosome, mRNA binds.
A. between the subunits
B. to the large subunit
C. to the small subunit
D. none of these
Answer: Option C