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CB1131- Intro to Biomolecular Engineering > Week 2-Making of Parts- Transcription and Translation > Flashcards

Week 2-Making of Parts- Transcription and Translation Flashcards

1
Q

What is transcription

A

A process whereby DNA provides information to mRNA

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2
Q

What is translation

A

Protein synthesis from mRNA

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3
Q

Definition of Ribonucleic Acids

A
  1. Nucleotide (DNA): Deoxyribose sugar + Nitrogenous base + Phosphate
  2. Nucleotide (RNA): Ribose sugar + Nitrogenous base + Phosphate
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4
Q

Structural Perspective of Ribonucleic Acids

A
  • Nitrogenous Base:
    1. Purines - Adenine and Guanine
    2. Pyrimidines - Cytosine and Thymine
  • Complementary bases:
    1. A=T (2H bonds)
    2. G=C (3H bonds)
  • Joined by H bonds to form sugar-phosphate backbones
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5
Q

Primary functions of DNA

A
  1. Storage of genetic information
  2. Replication and Inheritance
  3. Expression of Genetic message
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6
Q

Storage of Genetic information

A
  • Determines all inheritable characteristics
  • Nucleotide sequences with gene determines protein to synthesized
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7
Q

Replication and Inheritance

A
  • DNA must be copied accurately via replication
  • Transmit genetic information to daughter cells
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8
Q

Expression of genetic message

A
  • Genes encode proteins consisting of amino acids
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9
Q

What are the Classes of RNA

A
  1. rRNA - ribosomal RNA
  2. tRNA - transfer RNA
  3. mRNA - messenger RNA
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10
Q

What are ribosomal RNA

A
  • 75 to 80% of cellular RNA
  • rRNA together with protein form ribosomes
  • Produced in the nucleus
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11
Q

General of Features of Transcription

A
  1. RNA polymerase
  2. Initiation: promoters
  3. Elongation
  4. Termination
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12
Q

What RNA Polymerase

A
  • RNA Polymerase (DNA Dependent- RNA polymerase) catalyzes transcription in all cells
  • Function is to incorporate nucleotides to RNA strands during transcription
  • The RNA formed is complementary to one of the DNA strands
  • 5’ACGT 3’
  • 3’UGCA 5’
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13
Q

Transcription

A
  • mRNA synthesized by RNA polymerase II
  • First Step: Pre-initiation complex assembly
    1. Specific binding of protein to the eukaryotic promoter at 24 to 32 bases upstream of the initiation site known as the TATA box
    2. The binding protein is called TATA- binding protein
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14
Q

Why does it not start right after the TATA box

A

Due to the size of the TATA box binding protein

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15
Q

What is initiation

A
  • It is the beginning of transcription
  • The RNA polymerase binds to a region of a gene called the promoter
  • This signals the DNA to unwind so the enzyme can read the bases in one of the DNA strands
  • The enzyme is now ready to make a strand of mRNA with a complementary sequence of bases
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16
Q

Why is it the TATA box starting the transcription

A

A=T bonding is 2 H bonds hence it is easier to open up

17
Q

What is elongation

A

Polymerase move along DNA in 3’ to 5’ direction (towards the 5’ end) laying down complementary RNA in 5’ to 3’ direction, unwinding the DNA temporarily as it moves along the DNA template

18
Q

What is termination

A
  • Termination includes cleavage of mRNA and the addition of Poly-adenosine tail
  • Termination signal - AATAAA
19
Q

What is the purpose of a poly-a tail

A

Protects the mRNA from premature degradation by exonucleases

20
Q

What is modification

A
    • Contains non-coding segments called untranslated regions, at end 5’ and 3’ which plays regulatory roles
  • Consist of a methylated guanosine cap at the 5’ end and a string of adenosine residues of poly(A) tail at 3’ end
21
Q

Genetic Code and tRNA

A
  • DNA carries information for protein
  • Represents as genetic code
  • Each amino acid is encoded by 3 sequential nucleotides: codon for amino acid were nucleotide triplets
  • Decoding information in mRNAs is done by tRNAs (tRNAs are adaptors: specify amino acid and consist of anticodons)
22
Q

What are tRNAs

A
  • Transcribed by RNA polymerase III
  • Genes in DNA encoding tRNAs
    1. organized in tandem array
    2. separated by non-transcribed spacer sequences
    3. Found in small clusters scattered around genome
  • Matured tRNAs have triplet nucleotides CCA at 3’ end
  • tRNAs play key role in translation (protein synthesis)
23
Q

The genetic code

A
  • 4 bases for triple nucleotides
  • 64 possible mRNA codons combinations
  • In fact 61 different codons specify 20 amino acids (wobble hypothesis)
  • 3 stop codons
24
Q

What is the wobble hypothesis

A

The steric requirement between the anticodon and the codon is very strict for the first 2 positions and more flexible for the 3rd position

25
Q

Elaboration on the wobble hypothesis

A

2 codons specifying same AA but differ at 3rd position should use same tRNA in protein synthesis

26
Q

Snapshots of Translation

A

Translation: Protein Synthesis
Process involving:
- mRNA
-tRNNA with appropriate AAs
- Ribosomes
- Numerous proteins of specific functions
3 distinct steps: Initiation, elongation and termination

27
Q

Protein Translation: initiation

A
  • Ribosome attaches to precise site called initiation codon of mRNA
  • Ribosome moves along and read from one codon to the next in consecutive 3 nucleotides
  • For example, the ribosome moves from the initiation codon to the next codon and so on along the entire line
28
Q

Protein translation: elongation

A

The ribosome travelling down the message, reading codons and bring in proper aminoacyl tRNA’s to translate the message out to protein

29
Q

Protein translation: termination

A
  • Any of the 3 stop codons terminates the translation process
  • Ribosome disassembles for next round of translation
30
Q

Endoplasmic reticulum (RER)

A
  • ribosomes attached
  • membrane protein translation
  • secreted protein translation
31
Q

Intracellular Organelles: Rough ER

A

Synthesis of Secretory Protein
- mRNA binds to free ribosome
- N-terminal signal peptide syntheisized and target new protein to ER
- Recognition of SRP bound protein by SRP receptors
- Recognition of ribosome and membrane channel (BIP)
- SRP released, protein synthesis resumed and channel widened
- Protein released in ER lumen and ribosomes released for reuse

CB1131- Intro to Biomolecular Engineering (6 decks)

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