Cell Bio

Question 1

3 mechanisms of protein import into organelles

Answer 1

1. nuclear pores - for small proteins
2. protein translocators - membrane proteins. co translationally (ER) or post translationally (mitochondria and peroxisomes)
3. vesicles. ER to golgi, golgi to plasma membrane or lysosomes

Question 2

signal sequences direct proteins

Answer 2

often 3-60 AA sequences that recognizes membrane bound or soluble receptors
-signal peptidase often removes it after transport

Question 3

mitochondria structure/function

Answer 3

• produce ATP, apoptosis function
  a. outer membrane - porins for small molecules
  b. inner membrane space - cytochrome C for apoptosis and e transport chain
  c. inner membrane - forms cristae, has e transport chain and ATP synthase
  d. matrix space - enzymes for beta oxidation and CAC. also has mt genome and machinery for replication, transcription , translation

Question 4

import of proteins into mitochondria

Answer 4

• post translation
• binds to TOM and diffuse laterally until it reaches TIM complex
• moves through unfolded
• chaperone proteins help it move through and then fold it
• signal peptidase removes signal sequence once inside mitochondria
• requires ATP hydrolysis and electrochemical gradient

Question 5

mitochondrial genome structure

Answer 5

• double strand, circular
• 37 genes and makes 13 proteins for e transport chain and ATP synthase
• 1 promoter per strand
• 10-20 copies per mitochondria

Question 6

mitochondrial protein synthesis

Answer 6

replication - amount of DNA doubles with every cycle on average. not restricted to S phase
transcription - makes 1 large RNA thats cut into 2 rRNA, 22 tRNA, 13 mRNA
-translation - makes 13 proteins needed for e transport chain and ATP synthase
-many mitochondrial proteins made in cytosol and come in post translation

Question 7

mtDNA inheritance

Answer 7

• from mother. which doesnot affect mutation rate
• mothers mitochondria usually hteroplasmic - has normal and mutant mtDNA
• has to reach a certain amount before disease phenotype would appear
• more mutant leads to more severe disease
• may or may not pass on because all eggs have different amount of mutant
• homoplasmy is when all the mitochondria have a certain mutation

Question 8

differences in mitochondrial and nuclear genome and why mt DNA has high mutation rate

Answer 8

• mitochondrial is small, circular
• no introns, bad repair system, exposed to oxygen radicals, no histones makes for high mutation rate
• diseases are progressive bc of mutations and affect tissues that require a lot of ATP

Question 9

peroxisome function

Answer 9

• break down fatty acid, detoxify, make phospholipids
• oxidative degradation: add O2 to remove H2 and make H2O2
• catalase - add H2O2 to oxidize and then can convert excess peroxide into water
• beta oxidation -break long fatty acids into acetyl coA
• make cholesterol, bile acids and phospholipids: plasmogen is phospholipid in myelin sheath
• many proteins made in cytosol and brought inside post translation

Question 10

peroxisome defects

Answer 10

1. biogenesis - cant make peroxisome or it lacks enzymes
2. protein deficiency - just one protein missing

Adrenoleukodystrophy - dont have protein to bring long chain fatty acids inside. they build up and cause demyelination/nervous system defects and adrenal problems. get stem cell transplant or gene therapy.