Cells Alive Flashcards
Eukaryotes/ Prokaryotes
- Eukaryotes=
generally larger, nucleus within a nuclear membrane, membrane bound organelles. - Prokaryotes=
not as above
Organelles are cellular structures which are either membrane bound or non-membrane bound.
Membrane
a membrane defines the content of the cell, separating them from the external environment, giving a controlled internal environment for processes to occur. It must allow the cell to take in, exclude and excrete various substances in appropriate quantities and enable the cell to interact/communicate with its’ external environment; in the case of multicellular organisms this means enabling interaction with other cells.
Cellular compartments
Membranes:
- separate
- control
- enable
Phospholipid
are amphipathic.
A negatively charged phosphate group.
- The HYDROPHILIC HEADS in a membrane bilayer face outward
- Long, non-polar fatty acid tails which are HYDROPHOBIC
Spontaneously form bilayers.
The cell membrane is dynamic and fluid.
Contents of the bilayer
- cholesterol
- phospholipid
- protein
without cholesterol:
1) cold
rigid, not as fluid/ flexible, may break
2) hot
too fluid/flexible, won’t hold shape.
Proteins in Membranes
1) INTEGRAL PROTEINS
permanently attached.
- Transmembrane
span entire membrane (single pass, multiple passes) - Monotopic
each molecule is only on one side of membrane
2) PERIPHERAL PROTEINS
temporarily attached to membrane.
Mitochondria
organelles bound by a DOUBLE MEMBRANE:
- outer membrane
- inner membrane forms invaginations called CRISTAE
Space between membrane is INTERMEMBRANE SPACE.
Inside of mitochondrion is MITOCHONDRIAL MATRIX.
Mitochondria: Functions
- generate most of the energy a cell requires.
- most nutrients delivered to the cell are broken down in the cytoplasm to simple constituents which are transported to the mitochondria.
- constituents are further oxidised producing CO2 and H2O releasing energy captured in the form of ATP.
- are often located close to sites of high ATP utilisation.
ATP (Adenosine Triphosphate)
Adenosine = adenine + sugar
Energy release by hydrolysis of the phosphoanhydride bonds.
Energy used to fund energetically unfavourable reactions within a cell.
Mitochondria regenerate ATP from another source of energy.
Respiratory Stage 1:
Acetyl-CoA Production
Glucose converted to pyruvate in glycolysis.
Pyruvate converted in Acetyl-CoA in link reaction:
- remove a C
- Two C left converted to Acetyl-CoA
Fatty acids - long chain of carbons and a carboxylic acid:
- metabolised via beta-oxidation
- removes two C at a time
- two C converted to Acetyl-CoA.
AA Metabolism
Removal of amino group:
- Ammonia converted to urea in mammals, amphibians and sharks
- Ammonia converted to uric acid in birds, reptiles and insects
- Ammonia excreted directly in fish
Different amino acid carbon skeletons can enter at different points of a metabolic cycle.
Respiratory Stage 2:
Acetyl-CoA Oxidation
Acetyl-CoA feeds into the citric acid cycle or Krebs cycle.
End products:
- NADH
- FADH2
CO2 as waste from decarboxylations:
- one in link reaction
- two in TCA cycle
Respiratory Stage 3:
Oxidative Phosphorylation
NADH and FADH2 carry the electrons for the electron transport chain in oxidative phosphorylation:
- converts ADP+Pi to ATP
- O2 is reduced to H2O
Oxidative Phosphorylation - Electron Transport Chain
High energy electrons pass through complexes in the inner membrane, each with a higher redox potential than the last.
NADH -> NAD+ + H+ + 2e-
FADH2 -> FAD + 2H+ + 2e-
Final electron acceptor is oxygen.
Oxidative Phosphorylation -
Electrochemical Gradient
transfer of electrons from lower to higher affinity is ENERGETICALLY FAVOURABLE.
The energy released is used to pump H+ into the intermembrane space.
Pumping of H+ generates a electrochemical gradient across the inner mitochondrial membrane.
Oxidative Phosphorylation -
Proton Motive Force
ATP synthase:
enzyme that utilises energy from the electrochemical gradient to regenerate ATP from ADP and Pi.
Located within the inner membrane.
Hydrophilic pathway for H+ to flow down electrochemical gradient: CHEMIOSMOSIS, which is energetically favourable.
H+ flow causes rotation of the transmembranous rotor domain stalk.
Enzymatic head held still by an arm attached to the membrane.
The mechanical energy as the stalk grinds against the head is converted to chemical energy.
Transport in and out of the mitochondria: OUTER MEMBRANE
The mitochondria use and generate various compounds which need to be transported in and out.
The outer membrane contains large pores made of proteins called PORINS and is permeable to molecules of <5 kDa.
The gases oxygen and carbon dioxide diffuse freely across the membranes, down their respective concentration gradients - no energy or transporters needed.
Transport in and out of the mitochondria: INNER MEMBRANE
The electrochemical gradient is used to drive transport of other compounds.
Pyruvate and inorganic phosphate transport is driven by the H+m gradient, they are co-transported in the same direction (sympoter).
ATP and ADP are co-transported in opposite directions using the charge gradient (anti porter).
Mitochondrial Proteins
Most of the proteins destined for the mitochondria are encoded in the nucleus and produced by cytosolic ribosomes.
In the cytosol, mitochondria proteins are chaperoned by hsp70, which keeps them enfolded while their N-terminal signal peptides target them to the mitochondria.
Translocases of the Outer and Inner Mitochondrial membranes mediate passage into the mitochondria.
Transported is post-translational, process requires energy.
Mitochondrial DNA
They also possess their own genetic systems.
Their genomes are circular, vary in size and number of genes encodes.
Transcription and translation occur in the matrix carried out by complexes unique to the organelle.
Several genome copies per organelle and multiple organelles per cell, however DNA is maternally inherited.
They grow and divide by FISSION.
Clinical Relevance:
Mitochondrial Toxicity
1) TCA cycle inhibitors
2) Electron Transport inhibitors
Environmental toxins can prevent the passing of electrons by binding to one or more of the proteins that carry electrons.
3) Uncoupling agents
4) Mitochondrial Transporter inhibitors
Origins of Mitochondria + other functions
Mitochondria contain their own DNA and ribosomes.
Grow and divide by FISSION, own genome, own translation and transcription processes.
Evidence mitochondria originated by ENDOSYMBIOSIS.
Other functions:
- Apoptosis
release of cytochrome
- Calcium store
- Regulation of Cellular Redox State
- Haeme synthesis
many enzymes and carrier molecules have a co-ordinated haeme group at their active site.
- Steroid synthesis
- Cell specific functions
detoxify ammonia.
The Cytoskeleton: Functions and What is it
it is DYNAMIC.
It is composed of 3 distinct types of FILAMENTS:
1) MICROFILAMENTS
2) INTERMEDIATE FILAMENTS
3) MICROTUBULES
Functions:
- support
- movement
- resistance to mechanical forces
Cytoskeletal elements: MICROFILAMENTS
- Actin
- 5-9 nm
Made of the globular protein actin which assembles into two stranded helical polymers.
Dispersed through the cell, but concentrated beneath the cortex.
Functions: cell shape and motility
Cytoskeletal elements: INTERMEDIATE FILAMENTS
- 10 nm diameter
Various intermediate filament proteins which are themselves filamentous.
Extended alfa helical regions wind together into dimers, which then associate into tetramers that wind together to form rope-like fibres.
Functions:
- mechanical support of cell structures
- less dynamic than microfilaments and microtubules
Cytoskeletal elements: MICROTUBULES
- 25 nm in diameter
- made of the globular protein tubule
- these dimerise and then form hollow tubules
- more rigid than actin filaments -> long and straight
- one end (-) is attached to a microtubules organising centre while the other end (+) grows and shrinks.
Function:
- positioning organelles
- intracellular transport
Dynamics of the Cytoskeleton
The regular and parallel orientation of microfilaments and microtubules gives them STRUCTURAL POLARITY.
In a structurally polar filament Koff and Kon are often greater at one end than on the other. So if some circumstances facilitate the polymerisation at one end, this end elongates much faster than the opposite.
If however the concentration of three monomers falls below the Cc, then this end is also one that depolymerise fastest. This end of the filament is called the Plus end (+) whereas the other is called Minus end (-).
Monomers form end-to-end and side-to-side interactions. Interactions are non-covalent therefore rapid assembly/disassembly:
NON-CONVALENT BONDS to be broken.
MICROTUBULES: dynamic instability
The + end of a microtubule contains tubules bound to GTP : GTP cap.
Tubulin is a GTPase and hydrolyses its GTP soon after the incorporation into the microtubule.
If new GTP, tubulin is not added to the + end fast enough, GTP-tubulin is exposed at the + end.
This favours the disassembling of the microtubule.
