Unit 1 Flashcards
Cell Biology (40 cards)
1
Q
Nuclear Lamina
A
- Beneath the phospholipid bi-layer
- Stops at the nuclear probe
- Supports the nuclear envelope
- Integrity determined by phosphorylation / dephosphorylation
2
Q
Nuclear Pore
A
- 30 different proteins: 400 polypeptides
- Proteins lining the channel are hydrophobic
3
Q
Small GTP-Binding protein
A
- When bound to GTP it is “active”
4
Q
Ran-GTP
A
- Small GTP-binding protein
- Once active, can bind to an effector
- To deactivate Ran-GTP, it is hydrolysed by GAP
- To activate it, GDP is removed by GEF, and GTP is added to Ran by GEF
5
Q
Effectors
A
- Bind to active proteins
6
Q
NLS Proteins
A
- Allows proteins to be in nucleus
- Ran-GTP binds to importin, releasing NLS protein from importin α / β
- Ran-GTP in nucleus, Ran-GDP is in cytosol -> for import / export of importin α / β
- GAP is in cytosol, GEF is in the nucleus
- GEF is in the nucleus, so it has a NLS
7
Q
Eukaryotes’ Formation
A
- Formed from prokaryotes
- Cell membrane in prokaryotes invaginates into cell, encapsulating the nucleoid region, forms nucleus & endoplasmic reticulum
8
Q
Chromatin
A
- In mitosis, chromosomal DNA is packed into chromatin
- Chromatin are complexes of eukaryotic DNA & Proteins
- ~2X as many proteins as DNA
- Major proteins are histones
9
Q
Histones
A
- Small proteins that contain high % basic amino acids that facilitate binding to negatively charged DNA
- 5 Major Histones: H1, H2A, H2B, H3, H4
- DNA wrapped around an octamer of histones H2A, H2B, H3, AND H4 in nucleosome core particle and sealed by H1. 7-fold compaction of DNA
- Non-Histone proteins bind to linker DNA between nucleosome core particles
10
Q
Euchromatin v.s. Heterochromatin
A
- Euchromatin disperses again after mitosis
- Heterochromatin condensed in interphase
- Constituative heterochromatin:
a.) Always condensed mostly around centromeres / telomeres
b.) Consists of highly repeated sequences and few genes - Facultative heterochromatin is incactivated during certain phases of the organism’s life
11
Q
Mitochondrial Structure
A
- Can appear highly branched, with tubular structure (~4μm length)
- In mitochondria there is:
a.) Enzymes for Kreb’s cycle, of for expression of mitochondrial genes
b.) Several copies of circular DNA
c.) Mitochondrial ribosome
d.) Inner mitochondrial membrane: Principal site of ATP synthase
e.) Outer membrane: Contains enzymes that convert lipid substrates to focus that are metabolized in the matrix
12
Q
Types of carriers
A
- Flavoproteins contain NAD+, FAD+ prosthetic groups
- Cytochromes, contain heme groups Fe3+ -> Fe2+ (e.g. cytochromes)
- Copper containing proteins, Cu2+ -> Cu+
- Ubquinone (or Coenzyme Q), only carrier to not associate with a protein
- Iron-Sulfur proteins
13
Q
Reactions in Mitochondrial matrix
A
1.) e- derived from either NADH (via complex I or NADH dehydrogenase) or FADH2 (complex II or succinate dehydrogenase) are passed to ubiquinone (Q / UQ), a lipid-soluble molecule
2.) e- are then passed from Coenzyme Q to complex III (or cytochrome b-c1 complex)
3.) e- then transferred to cytochrome c, a peripheral membrane protein, which carriers e- to complex IV (or cytochrome oxidase)
4.) Complex IV transfers e- to molecular oxygen to form H2O within the matrix
5.) e- transfers in complexes I, III and IV generate energy, used to pump protons from the matrix to the intermembrane space, establishing a proton gradient across inner membrane. E stored in proton gradient is used to drive ATP synthesis as protons flow back to matrix through complex V / ATP synthase
14
Q
Mitochondrial disorders
A
- Buildup of ROS (Reactive Oxygen Species) in mitochondria cause a 10-fold increase in mutation of mt (mitochondrial) DNA. Can cause neurological disorders
- Yeast colonies arise from loss of mt DNA
15
Q
Photosynthesis vs oxidative phosphorylation
A
- Both generate ATP through a proton pump
- Both have DNA & ribosomes
- Both are surrounded by a double membrane
- Chloroplasts contain a 3rd membrane while inner mitochondrial membrane forms cristae
- Mitochondria rely on both a proton gradient & a charge gradient across inner membrane generating ATP, while chloroplasts rely on proton gradient
- ETC of both is composed of a # of large protein complexes
- Terminal e- acceptor in OP is O2 & in PSLR is NADP+
- OP requires O2 & produces CO2 while PSLR produces O2 & uses CO2
16
Q
Calvin cycle
A
- 18 ATP is used to generate sugar, which is used in OP to gain 30 ATP (net gain)
- RUBISCO is highly ineffecient
17
Q
Lumen
A
The inside of the compartment / organelle
18
Q
Orientation of proteins
A
Orientation in the endoplasmic reticulum = orientation anywhere else
19
Q
Endoplasmic Reticulum
A
- ER takes up ~50% of cell membrane
20
Q
rough Endoplasmic Reticulum
A
a.) Has ribosomes
b.) synthesise proteins including
i.) ER
ii.) golgi apparatus
iii.) lysosomes
iv.) secratory vesicles
v.) plasma membrane
21
Q
Proteins synthesised on free ribosomes go to:
A
- Nucleus
- Mitochondria
- Chloroplasts
- Deroxisomes
22
Q
Smooth ER
A
- Synthesis of lipids
a.) Inserted to cytosolic side of ER - Contributes to lipid composition of membranes of cell organelles
- After synthesis, lipids are transported by vesicles / carrier proteins
- Specialised function
a.) Synthesis of hormones in endocrine cells
b.) Detoxification of various organic compounds in liver cells
c.) Sequestration of calcium ion from cytoplasm of muscle cells
23
Q
Modifying lipids in membrane
A
- Enzymatic modification
- Modification during vesicle formation
- Modification by phospholipid transfer proteins
24
Q
Cisternae
A
- Stacks of flattened membranes
25
Transitional ER
- Secratory vesicles exit ER here en route to golgi apparatus
26
ER Folding a Protein
1.) Glucose residues are removed leaving a single terminal glucose
2.) Protein then associates with chaperones including calnerxin
3.) Terminal glucose is removed & if protein is not folded properly...
4.) ... UGGT enzyme adds glucose back...
5.) ... & folding is attempted again
6.) If protein then folds it can be transported to next compartment
7.) If it remains unfolded after several attempts, more sugars are removed...
8.) ... & protein is dislocated from ER to cytoplasm to be degraded by proteasome
27
Unfolded Protein Responce
- If too many unfolded proteins accumulate in ER, UPR is activated:
a.) Stops translation
b.) Degrades misfolded proteins
c.) Produces more chaperones
- Prolonged UPR leads to apoptosis
28
Golgi apparatus
- Located near nucleus (perinuclear)
1.) Factory in which proteins received from ER are:
a.) further glycosylated
b.) sorted for transport to their eventual destinations
i.) lysosomes
ii.) extracellular medium
2.) Some lipids are synthesised in golgi
3.) In plant cells, Golgi serves to synthesise polysaccharides for the cell wall
29
5 compartments of Golgi
1.) Cis Golgi network
2.) Cis compartment of Golgi stack
3.) Medial compartment of Golgi stack
4.) Trans compartment of Golgi stack
5.) Trans Golgi network
30
Movement of proteins in Golgi
- Vesicular transport: Cargo shuttled from CGN to TGN in vesicles
- Cisternal maturation: Each cisterna matures as it moves from cis face to trans face, mediated by vesicles travelling from trans face to cis face
31
Lysosomes
- Membrane-enclosed organelles that contain ~50 different degradative enzymes that can hydrolyse
a.) Nucleic acids (nucleases)
b.) Proteins (proteases)
c.) Lipids (Lipases)
d.) Carbohydrates (glycosidases)
- Acidic, because of proton pumps
32
Primary Lysosome
- Roughly spherical & do not contain obvious debris
33
Secondary Lysosome
- Larger & irregularily shaped; fusion of primary lysosomes with membrane-engulfed aged & defective organelles, contain particles of membranes in process of being digested
34
Autophagosomes can contain:
1. Organelles
2. Cytosolic proteins
3. Lipids
35
3 Pathways for delivering materials to lysosomes
Endocytosis: Digestion of molecules taken up from outside the cell
Phagocytosis: Digestion of large particles including bacteria, cell debris, & aged cells (from outside cell)
Autophagy: Digestion of aged / defective organelles
36
Gaucher's Disease
- Mutation in gene that encodes a lysosomal enzyme required for hydrolysis of glycolipid glucocerebroside to glucose & ceramide
- Treated using cerezyme, a modified form of glucocerebroside is taken by endocytosis & delivered to lysosome
- Other lysosomal diseases treated similarly (endosomes ultimately fuse with lysosomes)
37
Peroxisomes
- Site of synthesis & degradation of H2O2, (highly reactive & toxic), H2O2 is produced during oxidation of several substrates
- Serves to
1.) Oxidation of very long chain fatty acids (VLCFA)
a.) Heads to production of harmful H2O2
b.) In contrast to mitochondrial fatty acid oxidation, peroxisomal oxidation of fatty acids is not linked to ATP formation
2.) Decomposition of H2O2
3.) Biosynthesis of plasmalogens, a lipid that is abundant in myelin
4.) Conversion of stored fatty acids to carbs in germinating seeds of plants; critical to providing E for growth of germinating plant
38
Peroxisome & mitochondria
- Both formed from pre-existing organelles
- Both import preformed proteins from cytosol
- Both oxidise fatty acids
- Peroxisomes have 1 phospholipid bilayer, but mitochondria have 2
- Peroxisomes don't have DNA / ribosomes but mitochondria do
39
Cytoskeleton
Functions:
1. Provides structural framework of cell:
a.) Determines cell shape
b.) Determines general organisation of cytoplasm
2.) Responsible for movement of
a.) Entire cells
b.) Organelles
c.) Transport vesicles
d.) Chromosomes during cell division
40
Main kinds of cytoskeletal filaments
Microtubules:
- 25nm in diameter
- Built in polymers of protein tubulin
- Intracellular transport, cell division, cell organisation
Actin filaments:
- 8nm in diameter
- Built of the protein actin
- Motility, contractility
Intermediate filament:
- 10nm in diameter
- Built of a number of different proteins (70), some are tissue-specific
- Provide structural support & mechanical strength
