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7. Nucleic acids > Translation > Flashcards

Translation Flashcards

1
Q

What is translation?

A
  • It is the final step in the conversion of genetic information to proteins. It involves the mature mRNA and matching its codons to amino acids
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2
Q

What are the three stages of translation?

A
  • Initiation, elongation and termination

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3
Q

What are the sites of the large ribosomal sub unit called?

A
  • A site: Amino-acyl- tRNA
  • P site: Peptidyl-tRNA
  • E site: Exit
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4
Q

Explain the initiation process of translation.

A
  • The mature mRNA binds to a small ribosomal sub unit which contains the corresponding mRNA binding site
  • The tRNA carries amino acids at its 3’ end, at the bottom it has an anticodon
  • The initiator tRNA matches its anticodon with the initiation codon of the mRNA
  • The structure then binds to the large ribosomal sub unit, this is known as the translation complex (mRNA, small ribosomal sub unit and amino acid)
  • The initiator tRNA contains methionine (type of amino acid)
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5
Q

Explain the process of elongation.

A
  • The large ribosomal sub unit contains three binding sites for tRNA, these sites are the A site, P site and E site
  • First the initiator tRNA goes to the P site. A new tRNA joins to the A site and preforms its function (provide amino acid).
  • The amino acid from the tRNA at the A site forms a peptide bond with the growing polypeptide chain and then this tRNA moves to the P site.
  • The polypeptide chain elongates (grows)
  • The P site is where the growing polypeptide chain is
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6
Q

Explain the process of termination.

A
  • This tRNA which is at the P site then goes to the E site. This is where the polypeptide chain leaves the ribosome
  • This happens at termination
  • A release factor binds to the A site and the translation complex disassembles. The large ribosomal sub unit falls off, as well as the amino acid and small ribosomal sub unit
  • The process start over again to eventually produce a protein for a specific function
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7
Q

What is the structure of eukaryotic ribosomes?

A
  • Ribosomes bind mRNA and tRNA to synthesis polypeptides and proteins. They are made out of proteins
  • The ribosomal RNA is used for catalytic activity. The small ribosomal sub unit contains an mRNA binding site. The large ribosomal sub unit contains three tRNA binding sites (A, P and E)
  • Ribosomes are found on the RER or freely floating in the cytosol
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8
Q

What is the structure of tRNA?

A
  • tRNA is a single-stranded RNA molecule that folds on itself to from a cloverleaf- shaped structure
  • It contains double-stranded regions (intramolecular base-pairing)
  • Three hairpin loops
  • One of the hairpin loops contain the anticodon which binds the the mRNA codon
  • Each tRNA contains an amino acid which is attached on the 3’ end
  • When binding with mRNA, the appropriate amino acid is transferred to the end of the growing polypeptide chain
  • The ribosome acts as enzymes to catalyse this reaction
  • The anticodon runs in the 3’ to 5’ direction so the mRNA codon is 5’ to 3’

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9
Q

How is the concept of enzyme-substrate specificity related to tRNA-activating enzymes?

A
  • Each tRNA molecules binds with a specific amino acid in the cytoplasm in a reaction catalysed by a tRNA-activating enzyme
  • Each enzyme is highly specific for an amino acid and the tRNA molecule that has the corresponding anticodon
  • The specificity is based on the matching shape of the anticodon of the tRNA and the enzyme, as well as the matching shape of the amino acid and the enzyme
  • Concept of enzyme-substrate specificity
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10
Q

What are the reactions of tRNA activation?

A
  • An amino acid and ATP energy bind to the tRNA-activating enzyme to from an amino acid-AMP complex and a PP (pyrophosphate) which is a high energy bond
  • Then a specific tRNA binds to the enzyme and the AMP complex is released
  • After this the tRNA molecules is ‘charged’ and can be used
  • The charged tRNA can now be used for translation
  • The tRNA-activating enzyme links the tRNA to a specific amino acid
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11
Q

What is the function of the ATP (phosphorylation)?

A
  • To create a high energy bond that is transferred to the tRNA molecule
  • The stored energy provides the majority of the energy used by the peptide bond formation during translation
  • Any mutated single tRNA will be inconsequential because it will compete with many ‘normal’ ones
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12
Q

What are polysomes?

A
  • Multiple ribosomes attached to the same mRNA to allow the synthesis of polypeptides to speed up
  • These ribosomes translate the mRNA sequence simultaneously
  • The ribosomes look like beads on a string (mRNA strand)
  • Polypeptide chain gets longer as ribosome move from 5’ end to the 3’ end
  • In prokaryotes much shorter chains than in eukaryotes
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13
Q

Where are the proteins in eukaryotes synthesized?

A
  • Proteins in eukaryotes are synthesized by ribosomes found freely circulating within the cytosol
  • Free ribosomes produce proteins used in the cell
  • Bound ribosomes on the RER synthesis proteins for secretion or used in lysosomes
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14
Q

What determines the destination of the protein?

A
  • Determined by the presence and absence of an initial signal sequence
  • The beginning of polypeptide chains contain the signal sequence. When it is present, the sequence is recognized by a single-recognition particle (SRP)
  • The SRP stops translation and binds to the SRP recognition protein on the RER (rough endoplasmic reticulum)
  • Translation re-begins, and the polypeptide chain is then transported by a vesicle of the Golgi apparatus for secretion or for the lysosome
    OR
  • The chain is used for internal functions and gets embedded into the RER
  • The signal sequence then undergoes post-transcriptional modification and the SRP is recycled once the polypeptide is completely synthesied

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15
Q

What is the difference in translation in eukaryotes and prokaryotes?

A
  • In eukaryotes the ribosomes are separated from the DNA or RNA by the nucleus
  • After transcription, the mRNA is transported from the nucleus to the ribosomes right before translation. This required modification to the RNA (capping and polyadenylation)
  • In prokaryotes there is no nucleus and translation immediately occurs after transcription. Ribosomes sometimes being translation while the mRNA is still transcribed
  • This works because both processes occur in the 5’ to 3’ direction
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16
Q

What is the primary structure of a polypeptide?

A
  • The first level of structural organization is the order/sequence of amino acids of the polypeptide chain
  • There are covalent peptide bonds between the amine and carboxyl groups of amino acids next to each other
  • Primary structures determine the interactions between R groups of different amino acids and therfore control all other levels of protein organization
17
Q

What is the secondary structure of polypeptides?

A
  • Folding of polypeptide in a repeating arrangement to form α-helices (alpha, coiled) and β-pleated (beta) sheets
  • The folding is due to the hydrogen bonding between the amine and carboxyl groups of amino acids that are not connected
  • Give polypeptide chain a level of stability
  • Hydrogen bonds between -NH groups of peptide bonds and -C=O groups of other peptide bonds found in the same chain.
18
Q

What is the tertiary structure of polypeptides?

A
  • Polypeptide chain coils and turns to form complex molecular shape (3D shape)
  • Caused by interactions between R groups, ionic bonds and hydrophobic interactions. Mainly by R group tho. No hydrogen bonds
  • Non-polar (hydrophobic) amino acids avoid exposure to aqueous solutions
  • Polar (hydrophilic) amino acids are located outside the protein
  • Tertiary structures are important for the function of the protein
19
Q

What is the quaternary structure of polypeptides?

A
  • Multiple polypeptides or prosthetic groups may interact to form single, larger, biologically active protein
  • Prosthetic groups: inorganic compound involved in protein structure of function
  • A protein containing a prosthetic group is called a conjugated protein
  • Structure held together by a variety of bonds (similar to tertiary)
  • E.g. hemoglobin with four heme groups (transport oxygen)
20
Q

What environmental factors affect the structures?

A
  • pH, salt concentrations, temperature affect the secondary, tertiary and quaternary structures of proteins
  • The proteins are denatured

7. Nucleic acids (3 decks)

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