Term
Describe Translation
1. Define
2. Initiation
3. Elongation
4. Termination |
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Definition
1. synthesis of proteins directed by mRNA
-must be folded into correct 3D shape
2. Initiation- specific met tRNA and mRNA bind to small subunit
-large subunit then joins
3. correct AA are added
-controlled by decoding center in small subunit
4. stop codon binds to release factor |
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Term
| Describe translational regulation |
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Definition
Two kinds: translational repression and noncoding microRNAs
global translation activity is related to:
1. cell stress 2. nutrient availability 3. GF stimulation |
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Term
| Describe translation regulation of ferritin |
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Definition
Ferritin: stores iron
When iron is absent, IRP binds to IRE (iron response element) in 5' UTR blocking translation
-binds upstream to interfere with ribosomal formation of 40s subunit
-it can also bind downstream to stabilize mRNA for translation of Transferrin (iron transporter) |
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Term
| Describe the relationship of IRP and Aconitase |
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Definition
*same enzyme!
-Iron regulatory protein regulates ferritin translation
-Aconitase is an intermediate of Krebs cycle
*same gene has two different functions |
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Term
| Describe translation repression in 3' UTR |
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Definition
-repressor binds to initiation factor eIF4E which interferes with interaction between eIF4G
-inhibits initiation
-also plays a role in localization (embryos)
-mRNAs in oocytes have shortened poly A tails
-lengthened when fertilized and can then be translated |
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Term
| Describe chaperone proteins |
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Definition
-facilitate folding of other proteins (maintain 3D shape)
-act as catalyst but don't become part of complex
-stabilize intermediates
-help proteins fold to lowest energy conformation |
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Term
Describe functions of chaperone proteins
1. translation
2. transport
3. heat shock |
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Definition
1. bind to nascent polypeptides being made on ribosomes
-chain must be protected from incorrect folding or aggregation with other proteins until synthesis is complete
2. partially unfolded proteins are transported across mitochondrial membrane
-chaperones in mitochondria facilitate further folding
3. chaperones that help proteins refold after partial denaturing due to heat
Hsp70- stabilize unfolded polypeptides by binding to hydrophobic regions |
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Term
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Definition
1. Hsp70 binds and brings to chaperonin after translation
2. chaperonin consists of subunits in two stacked rings
-isolates protein from cytosol as it folds it
*requires ATP to release from Hsp70 and to fold protein |
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Term
Describe the following two chaperones
1. PDI
2. Peptidyl prolyl isomerase |
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Definition
1. protein disulfide isomerase
-catalyzes disulfide bond formation between cysteines
-breaks bonds and reforms to get correct shape
-present in ER because of oxidizing environment
(-SH is reduced S-S is oxidized)
2. assists in isomerization of cis and trans configurations of prolines |
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Term
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Definition
-cleavage of polypeptide chain removes portions
ex. initiator methionine from amino terminus
signal sequences- chain that target protein for specific transport (hydrophobic)
-inserted into membrane channel as protein emerges from ribosome and rest of protein passes through as translation proceeds
-signal is cleaved by signal peptidase
-Insulin is cleaved to make final product
-HIV cleaves viral proteins |
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Term
Describe glycosylation
1. Definition
2. Function |
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Definition
1. modification of proteins where a sugar is added
2. changes shape and adds protection
protein folding in ER, targeting proteins for transport, and recognition sites in cell-cell interactions
-localized to cell surface or secreted |
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Term
| Describe O- and N- linked glycoproteins |
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Definition
O: sugar is attached to O in Serine or Threonine (OH)
-N-acetylgalactosamine
N: sugar is attached to N in asparagine
-N-acetylglucosamine |
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Term
Describe the process of glycosylation
1. N-linked
2. O-linked |
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Definition
1. starts in ER before translation is complete
2. oligo is assembled on lipid carrier (dolichol phosphate) in ER
-built on dolichol phosphate
3. 14 oligo is transferred to asparagine of growing polypep chain
-glycosol transferase takes 14 oligo
1. N-linked modified by removal of 3 glucose residues
-removed in ER then mannose removed and other sugars added in Golgi
2. O-linked sugars are added one at a time
-all in Golgi |
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Term
Describe lipid addition to proteins
1. N-myristoylation
2. Prenylation
3. Palmitoylation
4. Glycolipids |
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Definition
1. myristic acid is attached to N-terminus Glycine
-inner face of plasma membrane
2. prenyl groups are attached to S from Cysteine
-involved in control of cell growth and differentiation (Ras)
3. palmitic acid is added to S from Cysteine
-association of proteins with inner membrane
4. lipids linked to oligos |
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Term
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Definition
-anchor proteins to the external plasma membrane
-contain phosphatidylinositol (GPI anchors)
-made in ER |
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Term
| Describe Protein Regulation |
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Definition
-regulate amount of proteins and activities
1. regulation by small molecules
2. phosphorylation
3. protein-protein interactions |
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Term
| Describe Protein Regulation: Small molecules |
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Definition
1. Allosteric regulation-feedback inhibition
ex. Phosphofructokinase- with ATP it goes slower (inhibitor) and with ADP it goes faster (activator)
2. GTP/GDP binding- changes conformation
-Ras elicits division when bound with GTP
*not covalent |
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Term
| Describe Protein Regulation: Phosphorylation |
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Definition
-reversible COVALENT modification to activate or inhibit protein
-catalyzed by protein kinases that add phosphate from ATP to OH on amino acids (Tyr, Ser and Threo)
-reversed using protein phosphatases |
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Term
Describe Protein Regulation: Kinases
Ex. epinephrine |
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Definition
-often involved in signal transduction pathways
ex. epinephrine signals breakdown of glycogen to glucose-1-phos to give more energy for muscle cells
1. epinephrine binds to adenylyl cyclase (allosteric) which converts ATP to cAMP
2. cAMP activates cAMP dependent protein kinase (allo)
3. phosphorylates phosphorylase kinase (coval)
4. phosphorylates glycogen phosphorylase (coval)
5. converts glycogen to glucose-1-phos
-all phosphates can be removed by phosphatases when epinephrine is removed |
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Term
Describe Protein Regulation: Protein-Protein interactions
Ex. cAMP dependent protein kinase |
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Definition
-interactions between polypeptide chains are important in regulation
1. cAMP dependent kinase is two catalytic and two regulatory subunits
2. cAMP binds and changes shape so the regulatory units can be released
3. catalytic units are free to work as enzymes
*allosteric |
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Term
| Describe Protein Degradation |
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Definition
-protein levels are determined by rates of synthesis/degradation
-many regulatory proteins have short half-lives
-damaged or faulty proteins are recognized and rapidly degraded |
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Term
| Describe Protein Degradation: Ubiquitin-Proteasome Pathway |
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Definition
Ubiquitin-highly conserved in eukaryotes
-marker that targets proteins for rapid degradation
1. faulty protein is marked with ubiquitin on lysine (ATP)
a. E1 attaches to and activates ubiquitin
b. E2 transfer ubiquitin
c. specific E3 transfer ubiquitin and attach to protein
2. additional ubiquitin are added
3. recognized and degraded by proteasome (ATP)
4. ubiquitin is recycled
ex. cyclins that regulate cell cycle |
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Term
| Describe Protein Degradation: Lysosomes |
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Definition
-contain digestive enzymes like proteases
-only function inside lysosome (pH=5)
-proteins are moved into lysosome by autophagy
-vesicles form around proteins and fuse with lysosome
Autophagy
1. nutrient starvation
2. insect metamorphosis |
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