Mol Lecture #36

Question 1

Cytoskeleton

Overview

Answer 1

• Cytoskeletal networks: 3 types
• Stable structures, but they’re also dynamic (cell is constantly restructuring them)

Question 2

Microtubules

Functions + Structure

Answer 2

• Provide tracks for vesicular transport (microtubule tracks to mive through organelles)
• Flagella and cilia (specialized functions to help move the cell or structures within the cell)
• Cell cycle- mitosis: kinetichore/non-kinetichore microtubules
• Hollow tubule made up of subunits: Called tubulin
  –> Tubulin has ‘+’ and ‘-’ ends (and so do microtubules) with different growth products
• Microtubules often radiate from centrioles located near the nucleus
• Many microtubules, but the density is higher towards the nucleus.

Question 3

Motor Proteins

Microtubules

Answer 3

• Dyneins and Kinesins
• Stably attach to some cargo and move along the cytoskeleton

Question 4

Intermediate Filaments

Answer 4

• Function in structural support and providing tensile strength
• Structure can occur as monomeric filaments, in parallel bundles, and in interconnected networks
  → Key element: highly elastic- can stretch several times their length.
  → think about the epithelial layers of the skin - ability to stretch
• Do not have a localization density- uniformly distributed

Question 5

Microfilaments (actin filaments)

Function

Answer 5

• They can anker membranes to other structures
• Provide tracks for vesicular transport
• Heavily involved in cell movement, maintaining cell shape
• Role in mitosis and cytokinesis

Question 6

Microfilaments

Structure

Answer 6

• Typically in 2 polymers of actin subunits (not covalently attached- just a lot of monomers, protein-protein interactions)
• Also have ‘+’ and ‘minus’ ends that grow and shrink at different rates (top to bottom like before)

Question 7

Non-covalent properties of Cytoskeleton Filaments

Answer 7

• exist between monomers in cytoskeletal filaments, or between ligands and their receptors
• The 3D shape of the involved proteins and the 3D shape at their interaction site matters/ chemical characterisitcs at the interation site matter.
• Proteins can be held together by non-covalent interactions at the binding site, including via hydrogen bonds, hydrophobic-hydrophobic interactions, polar-polar interactions, and charge-charge interactions.

Question 8

Motor Proteins

example

Answer 8

• Myosins- stably attach to some cargo, and move along the length of the filament

Question 9

Animal Cell interactions

Answer 9

• Cell adhesion molecules hold cells together (transient or semi-permanent interactions)
  Also allow cells to bind to things in the environment → extracellular matrix

Question 10

Cell Junctions

Answer 10

• Mediate more stable interactions between cells
• Anchoring junctions: stitching cells together tightly (have plaque (internal structure) and connected directly to the cytoskeleton). Two types based on which cytoskeletal element they bind to.
• Tight junction: forms between two cells so that nothing passes between them (epithelial cell layers, low permeability across cell layer - think digestive tract control)
• Gap junction: large protein channels (multi-protein channels)- think nuclear pore complex

Question 11

Specifics (These are more permanent adhesions)

Anchoring

Answer 11

-Anchoring Junction: adjoins cells using a structure known as a plaque that is connected to the cytoskeleton.
- Demosomes- intermediate filament connections
- Adherens junctions- microfilament connections

Question 12

Tight junctions:

Answer 12

creates tight seal between cells to prevent passage of molecules etc. between them.

Question 13

Gap Junctions:

Answer 13

• multiprotein channels that allow rapid passage of molecules (etc) between cells. (ex. Neurons and muscle cells)

Question 14

Extracellular Matrix

Answer 14

• Proteins are in the extracellular matrix and they’re often glycoproteins
• Integrin: transmembrane protein that can attach to microfilaments, and bind to proteins in the extracellular matrix

Question 15

Cell Signaling

Overview

Answer 15

• How cells communicate with other cells and they’re environment- important for single celled organisms, but critical for mutlicellular organisms
• Responses depend on cell type

Question 16

Distance Types

Answer 16

• Contact dependent- membrane bound type
• Paracrine- cell secretes something (signal- soluble) maybe 3-5 cells away
• Endocrine- soluble molecule that is secreted and can go long distances (hormones): Into the bloodstream
• Synaptic- type of signaling distance thats only foud in excitatory cells- neurons, muscle- (very small distances between them), difference that the first one because something is being passed across

Question 17

Steps (for paracrine and endocrine focus)

Answer 17

• Reception: signaling ligand (soluble entity released that is received by the receptor)
  –> Non-covalent interactions mediate the ligand binding, the same features that help proteins fold
• Signa transduction: translate and amplify the signal, involves a cascade or proteins translating the signal
• Response

Question 18

Reception

Answer 18

• Ligand (soluble): hydrophobic)(might be able to cross over the membrane) or hydrophilic (cannot get across the membrane, so we have receptors
  –> Often proteins, but often not
• Cells have many different receptor types on their surface. Cells can therefore recognize many ligand types. (possibly integrating many signals at once as well)

Question 19

Transduction

Answer 19

• Transforming a signal into one that can cause a cellular response. Often involves many proteins acting in sequence .

Question 20

Protein types:

Transduction

Answer 20

• Kinases
• GTPases
• Small molecule intermediates
• Ions that flux (transported across a membrane)

Question 21

Response

Macro v.s. Micro

Answer 21

• Macroresponse ( larger level)
• Move
• Cell cycle
• Die (programmed cell death)
• Differentiate
• Take on the characteristics of a different cell
• Create special products
• Microresponse (molecular level)
• Changes in the amount or activity of cellular components (ex. Cyclins, changing gene transcription, enzyme (allosteric regulation to change the things that are already there, or making more/less of something))

Question 22

Regulation

Answer 22

• Cell signaling pathways have to be turned off and can be modified by the cellular environment and other pathways.