Organelles Flashcards
How is the cell wall of a gram negative bacteria arrange?
Outer membrane
Cell wall
Plasma membrane
How is the arrangement of a gram positive bacteria?
Cell wall
Plasma membrane
What are the functions of the cell membrane?
- Enclose and protect cell
- Maintain structural and functional integrity
- Selectively permeable membrane
- Define inside/outside of organelles
- Compartmentalizations of biochemical activity
- Intercellular interaction and respond to external signal
- Scaffol for biochemical activity
What is the function of the golgi?
Maturation of glycoproteins and other components of membranes and secretory vessels
What is the function of chloroplasts (plants)?
Photosynthesis
What is the function of the mitochondria?
CTA, ET and oxidative phosphorylation
Fatty acid oxidation, amino acid catabolism and pyruvate oxidation
What is the function of lysosomes?
Segregation of hydrolytic enzymes such as ribonuclease and acid phosphatase
What is the function of the glycogen granules?
Glycogen synthesis and degradation
What is the function of the cytoskeleton?
Glycolysis; many reactions in gluconeogenesis, pentode phosphate pathway, activation of amino acids, fatty acid synthesis and nucleotide synthesis
What is the function of a vacuole?
Water storage
What is the function of the nucleus?
Replication of DNA, synthesis of tRNA, mRNA and some nuclear proteins
What is the function of the nucleolus
Synthesis of rRNA
What is the function of the ER?
Lipid synthesis, direction of biosynthetic products to their ultimate location
What is the function of ribosomes?
Protein synthesis
What is the function of microbodies?
Amino cid oxidation, catalase and peroxide reactions, sterol degradations; in plants, glyoxylate cycle reactions
What are the lipids in the cell membrane?
Phospholipids
Glycolipids
Cholesterol
What are the proteins in the cell membrane?
(Two classes: transmembrane and peripheral)
Membrane channels/pumps Transporters Membrane receptors Adhesion molecules Gap junctions
What are the 3 class of lipids?
Phospholipid (ex: phosphatidylcholine)
Triglyceride (ex: triacylglycerol)
Steroid (ex: cholesterol)
Where are glycolipids located?
Only on extracellular leaflet
What forms the glycocalyx?
The carbohydrate residues on the glycolipids
What is the purpose of cholesterol on the membrane?
For structural stability
Note: it’s on both leaflets
What determines the properties of a phospholipid?
The tail length and degree of saturation
What are some important phospholipids?
Phosphatidic acid (phosphate + glycerol)
Phosphatidyl-choline (choline + phosphate + glycerol)
Phosphatidyl-ethanolamine (ethanolamine + phosphate+ glycerol)
Phosphatidyl serine
Phosphatidyl-inositol
Sphingomyelin (choline and serine)
What do fatty acids form?
Micelles
What do phospholipids form?
Bilayers
Note: circular bilayers are liposomes
What holds the leaflet of a membrane together?
Van der Walls interactions (weak bonds between hydrophobic tails)
In a TEM, membranes appear trilaminar. Why is that?
The polar head groups attract osmium tetroxide and become dark
The center lipid section remains clear
How thick is the membrane?
7.5 mm thick
What is the membrane fluidity essential for?
Exocytosis, endocytosis, membrane trafficking and biogenesis
Why aren’t the inner and outer leaflets symmetric?
They are composed of different phospholipids
Where are glycoproteins and glycolipids on the membrane?
On the outer leaflet
What increases the fluidity of the membrane?
Unsaturated fatty acid tails (increase cis-double bond kinks)
Short chain
Increase temperature
What does cholesterol do to the membrane?
Increases stability by “filling in the gaps” when lipids are too fluid
I.e. If high unsaturation or high temp
What do steroid rigs do to PL hydrocarbon movement?
Reduces phospholipid movement
What happens when too much cholesterol is within a erythrocyte?
Distorted cell shape called acanthocytes
What does an acanthocyte look like?
Has 5-10 irregular, blunt, fingerlike projections
What is acanthocytosis (spur cells) anemia associated with??
Chronic liver disease
Why is spur cell anemia associated with chronic liver disease?
Abnormal lipoproteins with high cholesterol content and high plasma cholesterol levels in these patients
What does the decreased deformability of acanthocytes lead to?
Sequestration and destruction by spleen (haemolytic anemia)
What are lipid rafts rich in? (Butter islands in oil)
They are rich in cholesterol and glycosphingolipids (long saturated tails) and are less guild and thicker
What is a glyosylphosphatidylinositol anchor?
GPI: glycolipid that attaches proteins to PM
What kind of proteins are found in lipid rafts?
Integral and peripheral membrane proteins
Note: clustering enables proteins to function together and for transport into endocytic vesicles
E.i. GPI
What maintains the asymmetry of the phospholipid bilayer?
Flippases
Note: these enzymes selectively “flip” particular phospholipids across the membrane
What does flip-flop require? ( a type of movement within the bilayer)
Flippases
Scrambalases
What do scrambalases do?
Non-specific scrambling
In ER membrane: mix up newly synthesized PLs
At plasma membrane: activated during apoptosis
What is the functional importance of lipid movement?
Phosphatidyl serine will be flipped to outer leaflet during apoptosis
What are glycolipids used for?
Cell to cell recognition
Protection (exposed apical surface of epithelial cells)
Nerve conduction
What is the receptor for Cholera toxin found on the intestinal epithelial cells?
Gm1 ganglioside
What are integral proteins bound to?
Actin cytoskeleton
What is the difference in protein concentration in myelin and mitochondrial membrane?
Myelin : 25% protein
Mitochondrial: 75% protein
What are the functions of membrane proteins?
Transport (nutrients, metabolites, ions across bilayer)
Anchor membrane to macromolecules on either side
Receptors: signal transduction
Enzymes (lactase in apical membrane of GI epithelial cells)
Cell identity markers: MHC
What are the 3 classes of membrane proteins?
Integral transmembrane proteins
Peripheral proteins
Lipid-anchored (peripheral) proteins
What are the characterisitcs of integral transmembrane proteins?
Single/multipass proteins
Often alpha-helical in secondary protein structure
Receptors (signaling and adhesion), channels, transporters/pumps
What are the characteristics of peripheral proteins?
Located entirely outside but associated with inner/outer leaflet by noncovalent interactions
Part of cytoskeleton, cytochrome C
What are the characteristics of lipid-anchored (peripheral) proteins?
Located either side of bilayer, have lipid group that inserts into bilayer
Signaling and adhesion proteins
What does protein 4.1 link?
Actin to glycophorin (single pass transmembrane glycoprotein)
Note: also binds spectrin and band 3
What is band 3?
Multipass transmembrane protein
What does ankyrin bind?
Binds band 3; attaching spectrin cytoskeleton to membrane
What is hereditary spherocytosis?
An autosomal dominant disorder in RBC cytoskeleton membrane
This is due to non-functional skeletal membrane protein; spectrin, ankyrin or protein 4.1
What is dysfunctional in hereditary spherocytosis?
Spectrin, ankyrin or protein 4.1 (spectrin deficiency)
What is the treatment for hereditary spherocytosis?
Folate supplement, splenectomy
What are the effects of hereditary spherocytosis?
Unstable membrane, loses fragments
= RBCs sphenoidal, decreased deformability
-vulnerable to splenic sequestration and destruction
-hemolytic anaemia (splenomegaly, jaundice, gall stones)
What is the function of the apical plasma membrane?
Regulation of nutrient and water intake
Regulated secretion
Protection
What is the function of the lateral plasma membrane?
Cell contact and adhesion
Cell communication
What is the function of the basal membrane?
Cell-substratum contact
Generation of ion gradients
What does the glycocalyx repel?
Negative charges from sialic acid sugars
What are the substances found in the glycocalyx?
Glycoproteins, glycolipids, proteoglycans
What is different in the glycocalyx of a cancer cell?
Different sugar coat than noncancerous cells
What are the primary marker for cell recognition ?
Carbohydrates
What do carbohydrates provide for cell recognition?
Attachment for bacteria, viruses, toxins, other cells
Activated endothelial cells express selectins which bind to
oligosaccharides on WBC & platelets
L-selectins recognise addressins on lymphoid organ endothelial
cells
