chapter 4 Flashcards
1
Q
what are some roles the cytoskeleton plays?
A
- cell division and organelle transport
- responsible for maintaining the shape of a cell, and for chaning and modifying that shape in response to environmental needs
2
Q
what constitute a significant portion of the cytoskeletal system?
A
- the polymers of actin and tubulin
- provides the cell with its definitive shape and resistance to deformational force
3
Q
what are the 3 types of protein filaments found in the cytoskeleton?
A
- microfilaments
- intermediate filaments
- microtubules
- accessory proteins can regulate the function fo teh cytoskeleton by binding to these 3 types of filamentous proteins
4
Q
what are actin filaments?
A
- essential for cellular motility and maintaining the cell’s structure
- they also contrubute to cytokinesis during cell division, and interact with myosin during muscle contraction
- individual actin monomers are referred to as “G-actin” because they have a globular shape
- during polymerization, G-actin units are strung together to form “F-actin”
- 2 strands of F-actin form a microfilament
5
Q
what is treadmilling
A
- Treadmilling is a phenomenon observed in many cellular cytoskeletal filaments, especially in actin filaments and microtubules. It occurs when one end of a filament grows in length while the other end shrinks resulting in a section of filament seemingly “moving” across a stratum or the cytosol.
6
Q
what are intermediate filaments?
A
- intermediate in diameter between microfilaments and microtubules
- created from various types of protein subunits
- main featyre is a very long alpha-helical section
- flexible proteins
- typically found in the cytoplasm, between the nucleus and the p.m.
- their main function is to provide structural support and to help the cell adhere to neighboring cells
- ex. keratin
7
Q
what are microtubules?
A
- hollow cylinders composed of polymeric dimers of protiens known as alpha-tubulin and beta-tubulin
- involved in the movement of chromosomes during cell division, in intracellular transport, and neutrophil and amoeboid motility, and in the formation of cilia and flagella
8
Q
how is microtubule formation initiated and organized?
A
- in microtubule organizing centers (MTOCs)
- common MTOCs include the centrosome and the basal bodies found in cilia and flagella
9
Q
the building blocks of microtubules are alpha and beta-tubulin dimers, which polymerize end-to-edn in protofilaments in a?
A
- GTP dependent process
10
Q
in order for polymerization to occur, dimers must be present at a concentration at least equal to a minimum value known as?
A
- the critical concentration
11
Q
what are motor proteins?
A
- structural proteins that generate mechanical force as a result of undergoing conformational changes
- these proteins attach to the cytoskeletal filaments to transport cargo, and play a major role in sperm motility, the movement of unicellular organisms, intercellular transport mechanisms and force generation during muscle contraction
- ex. kinesins, dyenins, and myosins
12
Q
what are kinesins?
A
- energy from ATP powers the movement of kinesins, and they travel along microtubules and transport a diverse range of cellular cargo
- most commonly, kinesins move towards the positive end of the microtubule, which faces the periphery of the cell (anterograde transport)
- they are heterotetramers (4 distinct subunits)
- with each “step” kinesins take along its path, it hydrolyzes a molecule of ATP and then releases the leftover ADP
13
Q
what are dyneins?
A
- motor proteins that are structurally similar to kinesins but carry cargo and “walk” in the opposite direction- the minus end of a microtubule, whcih is usually oriented towards the center of the cell (retrograde trasnport)
- fall into 2 groups: axonemal and cytoplasmic
- axonemal are only found in cells with cilia or flagella and help generate the sliding motion between microtubules to move
- cytoplasmic are more common and transport the cargo needed to carry out regular cell functions
14
Q
what are myosins?
A
- they are ATPases, their main role is not transport, instead they play a central role in actin-based muscular contraction in muscle
- during skeletal muscle contraction, multiple myosin II molecules create force by a power stroke mechanism that makes use of the energy released by ATP hydrolysis, the power stroke occurs when myosin is tightly bound to actin. when inorganic phosphate is released from myosin following ATP hydrolysis, a conformational change occurs wherein actin is pulled toward myosin. the actin will remain attached until the subsequent binding of an ATP molecule triggers its release
15
Q
what re the molecules responsible for cell adhesion called?
A
cell adhesion molecules (CAMs)
- associated with cytoskeletal elements, but also play the additional role of anchoring cells to one another and to the extracellular matrix (ECM)
16
Q
what are the 3 groups of adhesion molecules?
A
- selectins
- cadhereins
- integrins
17
Q
what are selectins?
A
- mediate the inflammatory response
- found on immune cells, platelets, and the endothelial cells lining blood vessels
18
Q
what are cadherins?
A
- calcium-dependent CAMs that play a role in the early stages of growth and development and can bind to the microfilaments of the cell’s cytoplasm
- also form junctions known as adherens junctions that help link cells to each other within tissues
27
Q
Each Ig unit is composed of 2 heavy chains and 2 light chains:
A
- the heavy chains correspond to the vertical component of the Y shape
- light chains are present onlt in the uppermost diagnal part of the Y dhape
36
Q
what are the four different signalling that occur?
A
- autocrine- produced by and effect the same target cell
- juxtacrine- target cells in contact with signalling molecules
- paracrine- target cells in the general vicinity
- endocrine- signaling molecules that travel through the circulatory system to reach their target cells
40
Q
how do ion channel-linked receptors/ligand-gated ion channels work?
A
- act through synaptic signalling on electrically excitable cells.
- they undergo a conformational change when a ligand binds to them, such that a transmembrane pore is opened to allow the passage of a specific molecule
- the ligands to which the receptor binds can be neurotransmitters or peptide hormones, and the molecules that pass through are often ions, such as sodium or potassium
- the ion channels are only opened for a short time, after which the ligand disocciates from teh receptor, making the receptor available for a new ligand to bind
42
Q
how do RTK’s work?
A
- in RTK receptors, the trans-phosphorylated tyrosine provides a phosphorylated binding site for adaptor proteins, which help couple the signal to further downstrwam signalling processes
- ex. one of the signal transduction pathways that can be activated is known as the MAPK pathway
- the MAPL protien is a protein kinase that can attach phosphate to target protiens such as transcription factors, thereby altering gene transcription and cell cycle progression
43
Q
how do GPCRs work?
A
- G proteins are known as heterotrimers, because they are composed of 3 distinct alpha, beta and gamma subunits (spans 7 times)
- when bound to GDP, G proteins are inactive, but they become activated by binding to GTP. the way that this happens is that an intracellular component of the G protein receptor facilitates the exchange of a molecule of GDP for GTP at the alpha subunit
- once this takes place, the alpha subumit together with the bound GTP dissociates from the beta and gamma subunits
- at this point, the subunits of the G protein separate;y interact with effectors in the cell, triggering downstream signalling processes
- the alpha subunit has a certain basal level of GTP hydrolysis activity, which means that it will automatically eventually regenerate GDP. once GDP is regenerated, the G protein returns to its inactive state
- the rate of GTP hydrolysis can be accelerated by the actions of another family of allosteric modulating proteins, GTP-ase activating protein, AKA GAPs
