Chap 12/13/14 Flashcards
Actin filament diameter
7 nm
In what 2 major forms does actin exist in cells?
G actin and F actin
When is ATP hydrolyzed by actin?
After assembly but before disassembly
Critical Concentration
Concentration of actin monomers at which the rate of polymerization into filaments equals the rate of depolymerization
Each monomer of actin binds one molecule of which nucleotide triphosphate?
GTP
Where does treadmilling take place?
Concentration of free actin at the midpoint b/w the critical concentrations of the barbed and pointed ands of an actin filament
What drug blocks the assembly of actin filaments?
Cytochalasin
What stabilizes actin filaments?
Tropomyosin
What initiates branching of actin filaments?
Arp2/3
Actin filaments are bound into bundles of parallel filaments by what proteins?
Alpha actin and fimbrin
Short actin filaments bind tetramers of which protein to form the cytoskeleton of erythrocytes?
Spectrin
Duchenne’s muscular dystrophy is characterized by what?
X-chromosomal inheritance
Where are actin filaments anchored?
Adherens junctions
What happens with the A, I, and H bands during muscle contraction?
A stays same width. I and H shorten.
Where is the barbed (fast growing) end of actin filaments located in a muscle?
Z disc
What type of myosin is present in muscle sarcomeres?
Myosin II
Intermediate filaments diameter
8-11 nm
Intermediate filament function
Provide mechanical strength for cells
What makes up the intermediate filaments in the nucleus?
Lamins
Desmin filaments in muscle cells
Connect actin filaments to the plasma membrane at the ends of myofibrils
Keratin filaments are found in what cell types?
Epithelial cells
Of what type of cells is vimentin is the major intermediate filament protein?
Fibroblast
Where are keratin filaments anchored?
Junctions called desmosomes
Expression of a shortened skin keratin gene in place of the normal keratin gene in transgenic mice resulted in which phenotype?
No hair and fragile/easily blistered skin
ALS (Lou Gehrig’s Disease) can result from a mutation of what gene?
Neurofilament protein (Intermediate filament)
Microtubule Diameter
25 nm
Evolutionary ancestor of eukaryotic tubulins
Protein similar to bacterial protein FtsZ
Microtubules are assembled from what?
Dimers of alpha nd beta tubulin
Which nucleotide triphosphate is hydrolyzed during a cycle of microtubule assembly and disassembly?
GTP
Proteins Rab, Ran, and tubular are all what?
G proteins regulated by bound GTP or GDP
Treadmilling
The microtubule behavior in which tubulin adds at the plus end, fluxes through a constant-length microtubule, and comes off the minus end
Dynamic Instability
The microtubule behavior in which some microtubules are rapidly depolymerizing and some are growing
Both colchicine and colcemid do what?
Block microtubule assembly by binding to free tubulin
What does the anticancer drug taxol do?
Acts to stabilize microtubules and thus inhibit disassembly
What is the major microtubule-organizing centre in most animal cells?
Centrosome
What part of the microtubule is farthest from the centrosome at the end of interphase?
Plus end
Role of centrosome
Initiate microtubule growth
Kinesin 1 is a motor proteins consisting of what?
2 heavy chains and 2 light chains
The cargo carried by kinesin along microtubules binds to kinesin on which region?
Tail
Cytoplasmic dynein plays a key role in the positioning of which organelle?
Golgi apparatus
A male patient at a medical clinic presents with infertility due to nonmotile sperm and an inability to clear mucous from his respiratory tract. Other tissues are normal. What do you suspect that these symptoms may be caused by?
Mutant dynein
In a cilium or flagellum, _______microtubules are arranged _______.
9 doublet, in a circle around a central pair of microtubules
What are the basal bodies of cilia and flagella similar in structure to/can form from?
Centrioles
Why do adjacent microtubule doublets in cilia and flagella produce a banding movement?
Nexin links between microtubule doublets convert a sliding movement into a bending movement
The beating of cilia and flagella occurs by means of what?
Dynein-based microtubule sliding
Polar microtubules
Microtubules that overlap in the centre of the mitotic spindle
The drug taxol stabilizes microtubules so they cannot shorten. If taxol were added during anaphase of mitosis, what effect would you expect it to have on anaphase movements?
It would stop all movements
ADF/cofilin plays a role in what?
The disassembly of microfilaments
Actin may be cross linked into what?
Either parallel or contractile bundles
What is the basis for muscle contraction?
Sliding of myosin and actin fibres past one another
What is the major cation responsible for regulating actin-myosin contraction?
Ca 2+
To what do the tail(s) of myosin I or myosin V bind? Why?
Cargo such as membrane vesicles or intermediate filaments because they do not form thick filaments and yet are still capable of producing movement along actin filaments
The discovery that the intermediate filament protein keratin is essential for mechanical strength of epithelial cell layers was made in what?
Transgenic mice
What determines whether a microtubule grows or shrinks?
The rate of GTP-bound tubulin addition relative to the rate of tubulin GTP hydrolysis
Cenrosome
The major microtubule-organizing centre in animal cells
What are kinesis and dynein?
Microtubule motor proteins
14 - What gives the plasma membrane its barrier to passive diffusion?
Phospholipids
14 - Why are mammalian erythrocytes particularly useful for studies of the plasma membrane?
The only have the one membrane (the plasma membrane)
14 - Gorter and Grendel’s classic experiment allowed them to observe that the erythrocyte plasma membrane contains what?
Enough lipid to occupy a monolayer equal to twice the surface area of the erythrocytes
14 - How are plasma membrane phospholipids arranged?
Asymmetrically distributed between the two membrane halves
14 - Where is cholesterol present?
In the membranes of all animal cells
14 - Where are plasma membrane glycolipids found?
Exclusively in the outer leaflet
14 - Lipid rafts
Clusters of sphingolipids, cholesterol, and membrane proteins that move together laterally in the plane of the plasma membrane
14 - If a suspension of cells is frozen and fractured, what will be the most likely path of the fracture plane?
Between the two leaflets of the cell membranes
14 - What are the two erythrocyte proteins, glycophorin and band 3, examples of?
Transmembrane proteins
14 - How are membrane proteins able to move above the temperature at which lipids are fluid?
Laterally in the plane of a membrane
14 - Selectins
Cell-surface glycoproteins that mediate specific recognition between cell types such as leukocytes and endothelial cells of blood vessels
14 - What types of molecules diffuse passively across the plasma membrane most rapidly
Small and hydrophobic
14 - How does facilitated diffusion differ from passive diffusion?
Facilitated diffusion is mediated by a protein carrier or channel
14 - What does the glucose-facilitated diffusion transporter do?
Transport glucose into or out of the cell
14 - Ligan-gated channels
Channels that open in response to neurotransmitters or other signal molecules
14 - Resting potential of a typical eukaryotic cell?
-60 mV
14 - What does the Nernst equation calculate?
Equilibrium potential due to one ion
14 - What would be the resting potential across an artificial membrane if all charged molecules on both sides were equally permeable?
0 mV
14 - Why are voltage-sensitive K+ channels 1000x more permeable to K+ than to Na+?
A selectivity filter removes the water molecules from K+ ions but not from Na+ ions
14 - Active Transport
Transport in an energetically unfavourable direction always driven by hydrolysis of ATP
14 - What primarily produces the Na+ and K+ ion gradients across the plasma membrane?
Action of the Na+-K+ pump
14 - What percent of the ATP in a typical animal cell is consumed by the Na+-K+ pump?
25%
14 - Cystic fibrosis is a genetic disease in which thick mucus accumulates over several epithelia and eventually blocks the pulmonary airways. What is the molecular basis of this disease?
The production of a defective chloride channel
14 - What does gene therapy for CF involve?
Transfer into bronchial epithelia of the CFTR gene
14 - What is the function of the MDR ABC transporter in a number of animal cells?
To transport poisons and drugs out of cells
14 - What is the role of tight junctions in the transport of glucose across the intestinal epithelium?
They keep the Na+-glucose cotransporter in the apical membrane and the glucose-facilitated transporter in the basolateral membrane.
14 - What is coupled transport of glucose and Na+ into the intestinal epithelial cell an example of?
Symport
14 - What is the functioning of the Na+-Ca2+ transporter in the plasma membrane an example of?
Antiport
14 - Phagocytosis involves movement of the cell surface by what?
Actin-based motility
14 - Aged RBC are removed from circulation by what?
Macrophages in the spleen
14 - Phagocytosis is the main function of what two types of human white blood cells?
Macrophages and neutrophils
14 - Cholesterol is taken up into most cells of the body by what?
Receptor-mediated endocytosis
14 - Brown and Goldstein discovered the mechanism of cholesterol uptake by studying fibroblasts from children with which disease?
Familial hypercholesterolemia
14 - What is the primary reason that mammalian red blood cells are used in the study of the plasma membrane?
The lack nuclei and membrane-bound organelles
14 - What are 2 examples of membrane lipids present in small amounts?
Glycolipids and phosphatidylinositol
14 - What is a feature common to most transmembrane proteins?
An alpha-helical region of about 20-25 hydrophobic amino acids
14 - What is an example of an integral membrane protein that does not contain a transmembrane α helix?
Glycosylphosphatidylinositol (GPI) anchors
14 - Although Na+ is smaller than K+, its passage through the K+ channel is blocked by what?
The selectivity filter
14 - How does active transport differ from facilitated diffusion?
Active transport I evolves the transport of molecules up their concentration gradient
14 - What drives transportation of glucose into the intestinal epithelium?
Ion gradients established by the Na+-K+ pump
14 - Phagocytosis
Ingestion of large particles by cells (a form of endocytosis)
14 - LDL uptake by cells is one of the functions of what?
Receptor-mediated endycytosis
14 - Mutations in the internalization signal of endocytic receptors prevent their interaction with what?
Adaptor proteins
14 - pH of endoscopes and lysosomes
Acidic
Where are mitochondrial and chloroplast proteins synthesized?
On free cytosolic ribosomes
Cristae
Infoldings of the inner mitochondrial membrane
Matrix
Inner compartment of mitochondria
What product of glycolysis is transported into the mitochondria?
Pyruvate
The critic acid cycle consists of the incorporation of _______ and its oxidation to produce _______
acetate from acetyl CoA
CO2, NADH, and FADH2
Most small molecules are permeable across what?
The outer (but not inner) mitochondrial membrane
What do mitochondria contain genes for?
Mitochondrial proteins, rRNAs, and tRNAs
Endosymbiosis
Process by high mitochondria are though to have arisen during evolution
What do mitochondrial genomes usually consist of?
Circular DNA molecules
What organisms are most similar to mitochondria?
α-proteobacteria
How is mitochondrial DNA inherited?
By means of maternal transmission
Where are most mitochondrial proteins synthesized?
On cytoplasmic ribosomes. They are imported after they are completely synthesized.
What do mitochondrial targeting presequences usually consist of?
Positively charged α helix
Where are most mitochondrial phospholipids synthesized?
ER
What does import of mitochondrial proteins from the cytoplasm require?
A proton electrochemical gradient across the inner membrane
Where do the proteins encoded by the human mitochondrial genome function?
In mitochondrial ribosomes
What are Tim and Tom?
Protein translocations in mitochondrial membranes
Matrix-processing protease
Protease that cleaves off the mitochondrial protein presequence
How are mitochondrial inner membrane transmembrane proteins inserted into the inner membrane?
Through Tim
How do chloroplasts differ from mitochondria?
Chloroplasts synthesize their own amino acids and fatty acids
How are chloroplasts similar to mitochondria?
They both generate ATP by a chemiosmotic mechanism across the inner membrane
Where are carotenoids stored?
Chromoplasts
Grana
Stacks of thylakoids
What do chloroplast tRNAs translate?
All mRNA codons according to universal code
Where are most chloroplast proteins synthesized?
Free ribosomes in the cytosol
Where are proteins incorporated into the thylakoid lumen synthesized, imported, and transported?
Synthesized in the cytosol, imported into the stroma, and transported across the thylakoid membrane because of its second (hydrophobic) signal sequence
What do chloroplasts synthesize?
Amino acids
What do all plastids develop from? (including chloroplasts)
Proplastids
What is the most abundant protein on Earth?
Rubisco
Etioplast
Plastid that stores lipid
Tic and Toc
Complexes through which the transport of proteins across the outer and inner chloroplast membranes occurs
Where does the light-dependent generation of ATP in photosynthesis occur?
In the thylakoid membrane
Where does the dark reaction of photosynthesis occur?
In the stroma
What is the function of peroxisomes?
To oxidize certain organic molecules and degrade the H2O2 produced by these reactions
Where are most peroxisomal proteins synthesized?
On free ribosomes in the cytosol
Zellweger syndrome
Human disease caused by mutations in the proteins required for import of functional proteins into peroxisomes
How do plant peroxisomes convert fatty acids to sugars and other carbohydrates?
Via the glyoxylate cycle
How do new peroxisomes form?
By fusion of vesicles from the ER and growth and division of preexisting peroxisomes
How to mitochondria differ from other organelles?
Contain their own genomes
Where do human disease caused by mutations in mitochondrial genomes come from?
They are inherited by the mother
What is the normal function of dystrophin in muscle cells?
Links actin filaments to transmembrane proteins in the plasma membrane, which link to the extracellular matrix, helping to maintain cell stability during muscle contraction
Describe the myosin II molecule and its component parts.
The type in muscle. 2 heavy chains with globular head and long alpha helix tail (twist together when multiple). 2 light chains (wrap around heavy chain tail near head)
How does contraction of muscle cells happen?
Triggered by nerve impulses that stimulate the release of Ca 2+ from sarcoplasmic reticulum. Increased Ca concentration in cytosol affects tropomyosin and troponin (actin filament binding proteins). Tropomyosin binds lengthwise to actin and is also bound to troponins (binding action is blocked without Ca). Binding of Ca to troponin C shifts complex to all contraction.
How do plant cells initiate the formation of microtubules?
No centrioles to form microtubules so the pericentriolar material initiates microtubule assembly
How are the plus and minus ends of microtubules arranged in dendrites of neurons?
Microtubules are oriented in both directions
Tau Protein
MAP that is the main component of the lesions found in the brains of Alzheimer’s patients
In which directions do kinesin and dynein transport vesicles in an axon?
Kinesins move along microtubules to plus end and dyneins move to the minus end
How is contraction regulated in smooth muscle?
Regulated by phosphorylation of a myosin light chain. It is catalyzed by myosin light-chain kinase, which is regulated by the Ca2+-binding protein calmodulin.
Assuming that human mitochondria contain 1000–2000 different polypeptides, approximately what percent of the mitochondrial proteome is encoded by mitochondrial DNA?
1%
Where do the phospholipids in mitochondrial membranes originate?
ER
What is the major site of energy production in the form of ATP in human cells?
Inner mitochondrial matrix
What is the role of cytochrome C in the electron transport chain?
Transfer electrons from complex III to complex IV
In terms of its role in the generation of metabolic energy, the inner membrane in mitochondria is equivalent to which of the following in chloroplasts?
Thylakoid membrane
Chloroplast genomes contain approximately how many genes?
150
How many different translocon systems are used for protein import from the chloroplast stroma into the thylakoid lumen or membrane?
3
Where are carotenoids located and what do they do?
Chromoplasts, give plants their yellow/orange/red colours
Light is captured by how many different photosystems associated with the thylakoid membranes of chloroplasts?
2
What is the difference between the proton gradient across the inner mitochondrial membrane and the proton gradient across the thylakoid membrane of chloroplasts?
The first creates an electrochemical gradient, while the second is largely just a chemical gradient
All mitochondria use the universal genetic code - T/F
True
Some proteins destined for the intermembrane space are first imported into the matrix compartment - T/F
True
Frye and Edidin used fusion of human and mouse cells to demonstrate mobility of membrane proteins. Briefly describe the results of their experiment.
Within 40 mins after fusion, mouse and human proteins became intermixed over the surface of hybrid cells, indicating that they moved freely through the plasma membrane
Mitochondria contain 1000–2000 proteins - T/F
True
