Ch6 Part 2 Flashcards
Organelle
small structure within a cell that carries out a specific function.
Typically wrapped in on lipid bilayer.
Nucleus
Contained by the nuclear envelope.
Replication, transcription, and splicing occur in the nucleus.
Genome
Large size of the genome seems to drive the production of chromosomes.
If nuclei are treated with DNase and detergent, an insoluble component known as the nuclear matrix of nuclear scarf remains. Appears to contribute to structure. It may also play a role in gene expression.
Nucleolus
Ribosome factory consisting of: RNA polymerases (I), rRNA, and protein components of ribosome.
NOT separated by membrane from the rest of the nucleus.
Ribosomes are partially assembled in the nucleus, with proteins being transported into nucleus as ALL translation occurs outside the nucleus.
The nuclear envelope
Two lipid bilayer membranes (Inner and Outer).
ER is at points continuous with the outer membrane of the nuclear envelope. This makes the lumen of the ER continuous with the inter-membrane space of the nuclear envelope.
Has nuclear pores that permit the passage of material less than 60 kilodaltons.
Larger molecules must have a NUCLEAR LOCALIZATION SEQUENCE. This allows them to be translated onto a ribosome and transported into the nucleus.
Although RNA could technically diffuse passively through nuclear pores. Likely has a specific transport mechanism.
Mitochondria
Oxidative phosphorylation.
Bound by two membranes (inner and outer).
Inner membrane is where electron transport chain, ATP synthase, and proton gradient used to drive ATP synthesis is located.
Inner membrane is folded ie. cistae and is impenetrable to polar molecules.
Mitochondria Part 2
Has unique genome. Genome encodes rRNA and tRNA, as well as some components of electron transport chain and ATP synthesis.
Different system of transcription and translation. Including unique genetic code, RNA Pol., DNA replication machinery, ribosomes, and aminoacyl-tRNA synthestase.
Exhibit maternal inheritance.
Endosymbiotic theory
Mitochondria as separate organism brought into a larger cell.
Endoplasmic Reticulum
Can account for over half the membrane of some cells.
Rough ER - covered and ribosomes and produce proteins for the SECRETORY PATHWAY. Also directs protein traffic in the nucleus. Some glycosylation (though most in Golgi) and disulfide bonds here.
Smooth ER - not involved in protein synthesis, but can perform steroid synthesis in the gonads or degrade toxins in the liver.
Lumen - synonymous with the extracellular space.
Sites of Protein synthesis in the cell.
Cytoplasm or Rough ER
Protein synthesized by cytoplasmic ribosomes goes…
Peroxisomes, mitochondria, nucleus, or cytoplasm
Protein synthesized by the rough ER can go…
Secreted into environment
Become plasma membrane proteins
Travel to the membrane or interior of the ER, golgi apparatus, or lysosomes. Communication between these bodies via vessicles, so can be considered continuous.
Signal Sequence
At N-terminus, and determines where a protein in synthesized. All start in the cytoplasm.
Removed by a signal peptidase in the ER Lumen before transport to Golgi, Plasma Membrane, and potentially out to the exterior.
Signal Recognition particle
Recognizes the signal sequence and transports early polypeptide to Rough ER surface.
Integral Membrane Proteins
Processed slightly different than those with a signal sequence. They have TRANSMEMBRANE DOMAINS that are like a signal sequence but not at the N-terminus. They are not removed after translation.
During translation, transmembrane doomains are threaded through the ER membrane. Protein ends facing ER lumen will face exterior of cell.
Default target for proteins in the secretory pathway
Plasma membrane
Targeting Sequences
Required for any other destination on the secretory pathway besides the plasma membrane. (ie. Golgi, Lysosome, and ER)
Proteins destined for organelles not in secretory pathway require a LOCALIZATION SIGNAL.
Table 2. pg 177 good review!
Golgi Apparatus
Membranous sacks stacked together.
Functions to: Modify proteins from RER; Sort and send proteins to necessary destinations; makes some macromolecules like polysaccharides.
Direction of traffic in the Golgi
Mostly unidirectional.
Although retrogade traffic can occur if a protein intended for the ER ends up in the golgi apparatus.
Cis-stack: region closest to ER
Medial-stack: mid-region
Trans-stack: furthest region
Transfer of proteins and modification occurs from the Cis –> trans faces.
Constitutive Secretory Pathway
Proteins are sent from the golgi directly to the plasma membrane
Regulated secretory pathway
Some cells store secretory proteins for quick release, so they are stored in SECRETORY VESSICLES.
Lysosomes
Membrane bound.
Responsible for degradation of macromolecules via hydrolysis.
Produced in ER. Released from trans surface of the Golgi.
Crinophagy
Lysosomal digestion of secretory particles that are not needed.
Digested products are released into cytoplasm for resuse.
Acid Hydrolase
Enzymes contained in Lysosomes and mediate digestion.
Only function in low pH. A safety mechanism so that a rupture of a lysosome does not result in autophagy of the entire cell. Note though that if enough ruptured, pH could change enough.
Peroxisomes
Produce metabolic tasks.
Essential for lipid breakdown.
Have an enzyme that produced hydrogen peroxide as a byproduct. Another enzyme CATALASE; however, breaks it into H2O and O2.
Structure of animal cell membrane support…
Cytoskeleton
Three common lipids in lipid bilayer
Phospholipids, glycolipids, cholesterol
Phospholipid - Phophatidyl Choline (hydrophilic head with Choline, phosphate, and glycerol; two fatty acid tails)
Note: Sometimes however, there can be more proteins in a membrane than lipids. Ex. mitochondrial inner membrane.
Repair of a cellular membrane
Lipid bilayer is the lowest energy state of phospholipids, so a membrane will self-repair to reach lowest energy.
Integral Membrane Proteins
Have portion embedded in the membrane
Peripheral membrane proteins
Stuck to membrane and integral proteins via hydrogen bonding and electrostatic forces
Fluid Mosaic Model
Membrane is a mosaic of lipids free to move laterally. Proteins anchored to cytoskeleton are not free to move.
Cannot flip head over tail though. Membrane has “polarity”
Where does glycosylation occur on the cell membrane
Only on the extracellular surface. Likely because it occurs only in the rough ER and Golgi.
Molality (m)
moles of solute per mass (kg) of solvent:
Moles/Mass solvent
Note: Useful as molality does not change with temperature. And is roughly an approximation of molarity.
Mole Fraction
Moles substance / total moes in solution
Note: useful when more than one solute is present.
Ionizability factor
describes how many ions a molecule will produce in solution.
i = 1; no dissociation. this is true of most hormones, proteins, steroids etc.
Colligative Properties
Depend on the number of solute particles in solution rather than the type of molecule.
Four types on MCAT:
Vapour-pressure depression; boiling point elevation, freezing point depression; osmotic pressure.
Look at more sources on this!
Vapour Pressure Depression.
Vapour pressure refers to the pressure exerted by gaseous phase of liquid that evaporated from exposed liquid surface.
Substances that have high vapour pressure are volatile.
Vapour pressure depression occurs when a solute is added to a solution (ie. volatility is decreased). This substance will require more heat to reach vapour pressure.
Note that boiling will still occur at the same vapour pressure at sea level (760 torr) but more energy will be required to achieve this.
Boiling Pt Elevation
More solute particles, higher boiling point.
dT = kim
k - is solvent boiling point elevation constant. 0.5oC/molar concentration, for water.
i - is van’t Hoff factor
m - molar concentration of solution
Freezing point depression
Solute interferes with a liquids capacity to form a solid structure.
dT = -kim
-k - is solvent freezing point depression constant. 1.9oC/molar concentration, for water.
i - is van’t Hoff factor
m - molar concentration of solution
Osmosis
Type of diffusion in which a solvent diffuses, not the solute.
Tonicity
Describes osmosis gradients.
Isotonic - environment same as cell
Hypertonic/hyperosmotic
Hypotonic/hypoosmotic
Osmotic Pressure
Pressure required to stop Osmosis from happening. Only impacted by number of particles, not type.
π = MiRT
π - osmotic pressure in atm
M - molarity of solution
T- in Kelvins
Simple Diffusion
Diffusion through a membrane without assistance of a protein.
Ex. Steroid transit across the membrane
Contrast to FACILITATED DIFFUSION.
Differentiate two types of diffusion using kinetics. Facilitated diffusion exhibits saturation kinetics as relies on a finite number of membrane proteins.
Facilitated Diffusion
Gives quality of selective permeability.
Channel proteins or carrier proteins.
Carrier Proteins
Uniports - conformational change brings molecule across membrane
Symports - two molecules are brought across
Antiports - two molecules are brought across but in opposite directions.
Channel Proteins
Selective, and considered facilitated diffusion
Pores
non-selective tube through the membrane.
Formed from polypeptides known as porins.
Porins are large and so you do not find membranes with ion channels AND porins, as ion channels would be pointless.
Active Transport
Movement through membrane AGAINST a gradient
Primary Active Transport
Directly coupled to ATP hydrolysis.
Secondary Active Transport
ATP activity in indirect in its role of moving a molecule against the gradient.
For example glucose is transported against gradient when coupled with Na moving down its gradient. However Na gradient was established using an ATPase pump.
