7.3 Translation (HL) Flashcards by Enya Rastogi

What does the ribosome structure consist of?

Large subunit
Small subunit
3 tRNA binding sites (Large subunit)
mRNA + mRNA binding site (Small subunit)
Growing polypeptide chain

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tRNA molecule: What is the function of the acceptor stem?

Carries amino acid to combine with the growing polypeptide

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tRNA molecule: Function of hydrogen bonds

Holds the bases and molecule together into an L shaped tertiary structure

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tRNA molecule: Function of anticodon

Associates with mRNA codon via complementary base pairing

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tRNA molecule: Function of T arm + which side is it on?

Associates with ribosome via E, P, A binding sites

- On the right side

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tRNA molecule: Function of D arm + side it is on

Left side

- Associates with the tRNA activating enzyme

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Function of tRNA activating enzyme

It adds the amino acid to the acceptor stem

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Why is there more than one type of tRNA activating enzyme

Each tRNA molecule has different chemical properties

- Each amino acid is recognized by a specific enzyme although one enzyme may recognize multiple due to degeneracy

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How is tRNA activated?

Enzyme binds ATP to amino acid to form amino acid-AMP complex linked by high energy bond
Amino acid is coupled to tRNA and AMP is released
tRNA is now charged and ready for use

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Use of the energy transferred to charged tRNA molecule by ATP

Energy is transferred and stored energy will provide effort required for peptide bond formation during translation

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3 stages of translation

Initiation
Elongation
Termination

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What happens during initiation?

Mature mRNA binds to small ribosomal subunit and large subunit joins to complete assembly

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What is the first tRNA called and what does mRNA have to combine with it?

It’s called initiator tRNA and mRNA has a start codon (AUG) to link with it

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What happens during elongation?

A repeated cycle to create a growing polypeptide chain

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What is the A site and what happens?

Aminoacyl tRNA binding site

- Incoming tRNA with attached amino acid binds to chain

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What is the P site and what happens?

Peptidyl-tRNA binding site
Where tRNA from A site moves after amino acid forms peptide bond with chain.
Where the tRNA holding the chain is found

What is the E site and what happens?

Exit site
Where tRNA moves after transferring amino acid
Where it readies to detach from ribosome

What happens in termination?

Once termination codon is reached, release factor binds in A site and causes disassembly of components of translation complex. . i.e. ribosomal subunits, tRNA can all be reused

Why does translation occur immediately after transcription in prokaryotes?

Prokaryotes don’t have nuclear membrane so ribosomes directly bind to mRNA rather than wait for relocation to cytoplasm
In eukaryotes, mRNA is spliced and processed to create mature mRNA

Polysome

Structure that consists of multiple ribosomes attached to single mRNA

Purpose of polysome

Translates mRNA simultaneously to quickly create multiple copies of required protein

How do polysomes in prokaryotes differ from eukaryotes?

Prokaryotes: Chromosome may have numerous polysomes attached directly
Eukaryotes: Polysomes occur separately in cytoplasm or on ER as ribosomes attach to mRNA as it is being translated

What are bound ribosomes attached to?

Endoplasmic reticulum

Where do proteins synthesized by bound ribosomes go?

Outside the cell
ER
Golgi apparatus
Lysosomes
Plasma membranes

Bound ribosomes: What does beginning of the polypeptide contain?

Signal sequence that is recognized by SRP (Signal recognition particle)

Bound ribosomes: What happens after SRP binds to recognition protein on ER membrane?

After binding on ER, polypeptide enters rER as it grows

Bound ribosomes: What happens when translation ends?

- Complex disassembles | - Signal peptide is removed and whole protein is taken into rER

Bound ribosomes: What happens after protein is taken into rER?

Post-translational modifications and sorting of protein takes place in lumen of ER

What type of proteins do free ribosomes synthesize for?

- Proteins that are destined for mitochondria, chloroplasts, cytoplasm or nucleus of the cell

Difference between bound vs. free proteins

Bound proteins are meant for secretion or use in lysosomes while free proteins are mostly for intracellular use

Primary structure of protein

Protein is maintained by peptide bonds between subunits

Secondary structure of protein

- Folds back onto itself in beta-pleated sheets or alpha helices

Bonds in secondary structure

Stabilized by hydrogen bonds between -NH groups and C=O groups on different peptides in the same chain

Tertiary structure of protein

Further folding such that hydrophilic amino acids are outside and hydrophobic in the center

Bonding in tertiary structure

- Stabilized by interaction between R groups - Polar R groups have ionic interactions between acidic/basic groups or H bonding - Covalent bonds form between R groups with sulfur

Quaternary structure in proteins

More than one polypeptide chain where each chain is a subunit. Joined by similar bonds to tertiary

Conjugated protein

Quaternary structure which may have a prosthetic group that attaches to polypeptides

Properties of R groups

- Polar/hydrophilic - Non-polar/ hydrophobic - Positively/negatively charged - Some may contain sulfur