Exam 3: Translation Flashcards
Define translation
Translation is the biological polymerization of amino acids into polypeptide chains from information in mRNA
Polypeptides vs proteins
Polypeptides are precursors to proteins. Amino acids assembled on and released from ribosomes as polypeptides. Amino acid polymer.
Proteins are polypeptides folded up into a functional three-dimensional conformation.
List the molecules required for translation.
-amino acids
-transfer RNA (tRNA)
-messenger RNA (mRNA)
-ribosomes
Describe the basic structure and classification of amino acids.
Amino acids consist of a carboxyl, an amino group, and an R (radical) group all connected to a central C.
The R group determines the type of amino acid (Ex: Nonpolar: hydrophobic, Polar: hydrophilic, etc.)
Recognize the dehydration synthesis of a peptide bond
Dehydration (condensation) reaction facilitates bond between carboxyl group of one amino acid and amino group of another.
Describe tRNA
tRNA adapt genetic information present as specific triplet codons in mRNA to corresponding amino acids.
tRNA anticodons complement mRNAs
tRNAs carry corresponding amino acids after being “charged” by Aminoacyl tRNA synthetase
Describe the structure of the ribosome.
Ribosomes have an essential role in expression of genetic information.
They consist of ribosomal proteins and ribosomal RNAs (rRNAs) encoded by rDNA genes.
Consists of large and small subunits
70S vs 80S
Describe initiation, elongation, and termination of prokaryotic translation.
Initiation:
-IF3 (initiation factor) prevents premature binding of large and small substrate by binding to small subunit.
-The binding occurs at the Shine-Dalgarno sequence in prokaryotes
-IF1 blocks the A site from tRNA binding, allowing tRNA to bind to the AUG codon at the P site, escorted by IF2.
-IF3 released so the 50S subunit can bind, which triggers release of IF2 and IF1 by IF2 hydrolyzes energy (GTP) needed to complete the ribosomal complex and release IF1 and IF2.
Elongation:
-Second charged tRNA has entered A site, facilitated by EF-Tu
-Peptide bond forms, uncharged tRNA moves to E site and out of ribosome
-mRNA has been translocated 3 bases to the left causing charged tRNA to shift to P site
-First step has been completed, now a third charged tRNA is ready to enter the P site
Termination:
-Termination codon enters A site
-RF1 or RF2 stimulates hydrolysis of polypeptide from peptidyl tRNA
-Ribosomal subunits dissociate and mRNA released
-Polypeptide is folded into 3D conformation of protein, and charged tRNA is released.
Describe how polyribosomes impact production of translated gene products.
Polyribosomes/polysomes are mRNAs with several ribosomes translating at once.
As mRNA passes through a ribosome, its free to associate with another small subunit.
-Multiple ribosomes bind to the same mRNA molecule at different sites.
This allows multiple copies of a protein to be synthesized simultaneously from a single mRNA.
-Because several ribosomes are working on the same mRNA, the rate of protein synthesis is accelerated.
Compare and contrast pro- and eukaryotic translation
-Eukaryotic ribosomes are larger and longer lived
-In prokaryotes, the processes of transcription and translation occur simultaneously in the cytoplasm
-Kozak sequence in eukaryotes is considered to increase efficiency of translation by interacting with initiator tRNA
-Eukaryotic translation requires more factors for initiation, elongation, and termination than in bacteria
-In eukaryotes, initial recruitment of the ribosome to the mRNA is aided by 5’Methyl-cap binding proteins and PolyA tail binding proteins
-Some ribosomes are not free-floating; instead are associated with endoplasmic reticulum
Compare and contrast the four level of protein structure.
1: Sequence of amino acids
2: α-helix and β-pleated sheets. 2-D structure not involving R-groups
3: Three-dimensional conformation
4: Composed of more than one polypeptide chains
The tertiary structure is often considered the most important level of protein structure because it determines the 3D structure of proteins. The 3D structure is vital to protein function. For example, the catalytic activity of enzymes.
Describe importance of posttranslational modifications.
Polypeptide chains modified once they have been synthesized.
Modifications are crucial to functional capability of final protein product.
Ex:
-N-terminus amino acid removed or modified
– Individual amino acid residues modified
– Carbohydrate side chains are sometimes attached
– Polypeptide chains may be trimmed
– Signal sequences are removed
– Polypeptide chains often complexed with metals
Describe the importance of protein folding in protein function.
Proteins folding
– Not spontaneous
– Dependent on chaperones: Proteins that mediate
folding process
Diseases of protein folding
– Creutzfeldt-Jakob disease
– Transmittable brain disorder in mammals
– Presence of prions (misfolded proteins) in brain
Recognize the diversity of protein function in biology.
-Hemoglobin and myoglobin transport oxygen and important for cellular metabolism
-Collagen and keratin are structural proteins associated with skin,
connective tissue, hair of organisms
-Actin and myosin are contractile proteins found in muscle tissue
-Tubulin the basis of microtubule function in mitotic and meiotic spindle fibers
-Immunoglobulins function in immune system of vertebrates
-Transport proteins the movement of molecules across membranes
-Hormones and their receptors
–Histones
– Transcription factors
-Enzymes: Most diverse and extensive group of proteins. Specialize in catalyzing chemical reactions. Increase rate of chemical
reaction reaching equilibrium. Involved in biological
catalysis: Process whereby
enzymes lower energy of
activation for given reaction
Describe the structure of tRNA including the importance of posttranslational modifications.
-Small in size and very stable
-Cloverleaf structure
-Contain posttranscriptionally modified bases
-Modified nitrogenous bases prevent base pairing in loops involved in protein interactions contribute to wobbling in anticodons
