Organelles and Cytoskeleton Flashcards
What is chromatin?
Combined structure of proteins and DNA
What is the role of nuclear pores?
Allows mRNA strands to exit the nucleus and proteins to enter the nucleus
What type of RNA does the nucleolus produce?
Ribosomal RNA
What are synthesised at the nucleolus?
Ribosomes
What is the structure of the Golgi apparatus?
A single membrane consisting of cisternae
What is added to lysosomal enzymes by the golgi, why?
Mannose-6-phosphate
Keeps them sequestered
What is the role of the Golgi body?
Modifies proteins before packaging them into vesicles to leave the cell
What are the two faces of the golgi apparatus, what do they do?
Cis-face where vesicles are received from the ER
Trans-face where vesicles are send out after modification.
What is the structure of a mitochondria?
Oval shaped organelle, with a double membrane, the inner membrane is folded into cristae creating an internal matrix.
What is the function of the mitochondria double membrane?
Energy from the electron transport chain can be used to pump H+ into the intermembrane space so its chemiosmosis can drive ATP synthase to produce ATP.
What does the lysosome consist of?
Contains lyososymes which are digestive enzymes to degrade cellular waste
What enzymes are lysosymes?
Acid hydrolases
Why dont lysosymes digest cellular material?
Acidic nature - enzymes would be inactive in neutral pH.
How is the acidic pH maintained in lysosomes?
Proton pump that pumps H+ into the lysosymes.
Where are proteosomes present?
Nucleus and the cytoplasm
What is the role of proteosomes?
Breaks down proteins through proteolysis
How do proteosomes break down proteins?
Proteases are located in the central pore.
What identifies a protein for breakdown?
Ubiquitin
What metabolism are peroxisomes involved with?
Breakdown of very long chain fatty acids
What roles do peroxisomes have other than VLCFA?
Breakdown of D(enantiomer)-amino acids
Reduction of reactive oxygen species, specifically hydrogen peroxide
What are vesicles?
Small organelles containing a liquid or substance encased in a phospholipid bilayer
What are the important roles of vesicles?
Transporting substances across the cell, via MT pathways and driven by motor proteins
Transporting substances into and out of cells by endo and exocytosis
What is the structure of the RER?
Surrounds the nuclear membrane
Series of long fluid filled sacks that are dotted with ribosomes. It has many folds called cisternae
What is the role of the RER?
Protein synthesis and modification
What are the roles of the SER?
Lipid synthesis it also produces steroid hormones, and assists detoxification.
What is the fluid in the cytoplasm?
Cytosol
What are the three main roles of the cytoskeleton?
Movement: Cell motility
Cellular organisation: Moving organelles around a cell, vesicle transport for secretion.
Structure: Mechanical strength
What are the three major protein filaments of the cytoskeleton?
Microfilaments
Intermediate filaments
Microtubules
What is the diameter of microfilaments?
5-7nm
What is the diameter of intermediate filaments?
10-12nm
What is the diameter of microtubules?
25nm
What is the most notable microfilament?
Actin
Where are actin microfilaments concentrated?
Just below the cell membrane
What is meant by microfilament polarity, what is different at each end?
A plus end where growth and shrinkage are fast and a minus end where they are slow
How do actin filaments determine cell shape and movement?
Depolymerising and polymerising at the ends
How does actin determine cell movement (muscle in particular)?
Actin binding site forms a cross-bridge with the myosin head that leads to a power-stroke.
What proteins make microtubules?
Alpha and beta tubulin
Where do microtubules originate from?
Microtubule organising centre (MTOC).
What are the roles of microtubules?
Positions organelles, aids cell division and intracellular transport
What does the MTOC contain?
Two cylindrical shaped centrioles
Where do centrioles move in cell division?
To poles
Which end of the microtubule is embedded in the MTOC?
- end
Which end of the microtubule grows/shrinks faster?
+ end
What molecules favour growth and shrinkage of MT?
GTP favours growth, GDP favours shrinking
What is the name of proteins that move along MT?
Motor proteins
What do motor proteins require to move along MT?
ATP
What are the two key motor proteins and what direction does each one move cargo?
Kinesin moves from the MTOC to the plus end, dynein moves from the plus end to the minus end.
What is the role of MAPs?
Microtubule associated proteins (MAPs) bind the stabilise longer microtubules to encourage growth at the plus end.
What is the main role of intermediate filaments?
Maintain mechanical strength and structure
What are key examples of intermediate filaments?
Neurofilament, keratin and nuclear laminin proteins.
What holds keratin filments in place (2)?
Disulfide bond crosslinks as a result of many cysteine residues
Hemidesmosomes (basal lamina to cell)
What are the three main types of cell junction?
Anchoring
Occluding (tight)
Gap
What filaments underpin anchoring junctions?
Intermediate filaments
What are the three subcategories of anchoring junctions?
Desmosomes (cell to cell)
Hemidesmosome ( cell to basal lamina)
Adherens (cell to cell)
What intermediate filaments underpin anchoring junctions in epithelia?
Keratin
What intermediate filaments underpin anchoring junctions in cardiac cells?
Desmin
What are adherens, why are they different to desmosomes?
Cell to cell adhering junction
Connect actin filaments not intermediate
What is the role of tight junctions?
Dynamic seal that adjusts intercellular permeability acting as a barrier to harmful contents
What are the tight junction proteins?
Claudin and occludin
Describe the structure of a gap junction
6 transmembrane connexin proteins makes up a connexon complex
What is the function of gap junctions?
Couple cells chemically and electrically
What are several junctions that are important in tight epithelia?
Junctional complex
Zonula occludens
Zonula adherens
Macula adherns
Site for activation of sugars for oxidation
Cytoplasm
