Transcript motor protein - cloudfront.net

Chapter 7: A Tour of the Cell
Objectives
The student is responsible for:
1.
The definitions of all bold faced words in the chapter
2.
Knowing the entire chapter especially:
a)
Name, spelling and function of all organelles
b) Differences between prokaryotic and eukaryotic cells
Figure 7.0 Fluorescent stain of cell
Figure 7.2 Electron micrographs
TEM or Transmission Electron Mic.
Image of trachea of a rabbit
SEM or Scanning Electron Mic.
Image of trachea of a rabbit
Figure 7.3 Cell fractionation
How a cell can be separated into its components (fractionation)
Figure 7.4 A prokaryotic cell
Prokaryotes: Pro: before
Karyon: kernel (referring to
nucleus)
Figure 7.4x2 E. coli
Figure 7.5 Geometric relationships explain why most cells are microscopic
Figure 7.6 The plasma membrane
Animal Cell
Reference: Molecular Biology of the Cell CD

Media
 Animation
 9.2 Liver Cell View 2
Reference: Molecular Biology of the Cell CD

Media
 Animation
 1.4 Plant Cells
Figure 7.8 Overview
of a plant
Typical Plant
Cell cell
Figure 7.9 The nucleus and its envelope
Figure 7.x1 Nuclei Nucleus and Actin Within Cells
Figure 7.10 Ribosomes
Free and bound ribosomes have different functions
Figure 7.11 Endoplasmic reticulum (ER)
The ER manufactures membranes and performs many other biosynthetic functions
Functions of the Smooth ER

enzymes within the SER synthesize lipids, steroids, phospholipids

liver cells store lots of glucose in the form of glycogen. When glycogen is
broken down it first becomes glucose phosphate which cannot pass
through the cell membrane. An enzyme in the SER removes the
phosphate group so glucose can leave the cell.

detoxifies drugs, alcohol. The SER adds a hydroxyl group to the
metabolic by-products, making them water soluble. The more drugs
/alcohol you ingest, the more SER and enzymes your cells make thus
increasing tolerance. Also these same enzymes can provide tolerance to
other drugs because of their general action of adding hydroxyl groups.

also helps in muscle contraction by controlling the flow of calcium ions
required for contraction
The ER manufactures membranes and performs many other biosynthetic functions
Functions of the Rough ER

produces secretory proteins
 insulin is made by the RER
 the polypeptide (insulin) is modified inside the RER, new groups are
added to it; it gets properly folded.
 glycoproteins: a sugar/protein combo that is secreted.

these secretory proteins are carried from RER in vesicles

RER can become part of the membranes throughout the cell

Video: Molecular Biology of the Cell
 Video: 12.2 ER Tubules
Figure 7.12 The Golgi apparatus
Molecular Biology of the Cell: Media-Video: 13.2 Secretory Pathway
Figure 7.13 Lysosomes
Molecular Biology of the Cell: Media – Video 13.5 Phagocytosis
Contain enzymes to digest macromolecules
Work at a pH = 5; obtain the hydrogen ions from the cytosol
Compartmentalization: protection of the rest of the cell
Autophagy: recycling of the cells components (organelles or material in cytosol)
Lysosomes are involved in programmed cell death
Figure 7.14 The formation and functions of lysosomes (Layer 1)
Figure 7.14 The formation and functions of lysosomes (Layer 2)
Figure 7.14 The formation and functions of lysosomes (Layer 3)
Figure 7.15 The plant cell vacuole
Figure 7.16 Review: relationships among organelles of the endomembrane system
Figure 7.17 The mitochondrion, site of cellular respiration
Fundamental Characteristics of Mitochondria
1.
Can increase in number depending on cellular conditions or demands
2.
Contains its own DNA
3.
Can reproduce separately from the nuclear DNA
4.
Has TWO membranes, each a phospholipid bilayer
5.
Enzymes are embedded in each of the membranes
6.
Space between the outer and inner membrane is the intermembrane space.
7.
Within the cristae (inner most membrane) is the matrix.
8.
Enzymes in the matrix to help make ATP
9.
Cellular respiration occurs here and the subsequent ATP production
10. Molecular Biology of Cell CD: Chapter – 14.5 Tomograph of Mit
Figure 7.18 The chloroplast, site of photosynthesis
Fundamental Characteristics of Chloroplasts
1.
Can increase in number depending on cellular conditions or demands
2.
Contains its own DNA
3.
Can reproduce separately from the nuclear DNA
4.
Has TWO membranes, each a phospholipid bilayer
5.
Enzymes are embedded in each of the membranes
6.
Space between the outer and inner membrane is the intermembrane space.
7.
Stroma is the fluid within the chloroplast and contains enzymes
8.
Thylakoids are flattened sacs, stacked into grana and contain chlorophyll
9.
A chloroplast is a type of plastid.
10. Molecular Biology of Cell CD: Chapter – 14.5 Tomograph of Mit
Figure 7.19 Peroxisomes
Fundamental Characteristics of Peroxisomes
1.
Bound by single membrane
2.
Transfer hydrogen from different substrates to oxygen forming hydrogen
peroxide which is actually toxic to the cell.
3.
Catalase is present in the peroxisomes that breakdown the hydrogen
peroxide.
4.
When dormant seeds take in water, specialized peroxisomes, glyoxysomes,
convert fatty acids to sugars since the seeds cannot photosynthesize and
therefore cannot make their own sugars.
Fundamental Characteristics of the Cytoskeleton
1.
The cytoskeleton is a system of filaments of proteins that:
a)
Helps cells to organize their internal space
b) Interact mechanically with their environment
c)
Allow the cell to change shape and move
d) Allow the cell to move its internal components on tracks
2.
All of these functions depend on three main types of filaments
a)
Intermediate Filaments: provide mechanical strength and resistance to
shear stress
b) Microtubules: determine the position of organelles and direct
intracellular transport
c)
Actin Filaments: determine cell shape and whole-cell locomotion
3.
All three of these cytoskeletal filaments depend upon accessory proteins
a)
These accessory proteins control the assembly of the cytoskeletal
filaments in their particular locations.
b) A most notable accessory protein is a motor protein(s) that move
organelles along the filaments or move the filaments themselves.
c)
4.
Examples: mitotic spindle or spindle that a pulls the chromosomes
apart; cilia and flagella; tracks for vesicles to move down in the axon of
the nerve cell; contractile ring during cytokinesis.
Molecular Biology of the Cell
a)
Chapter – 16.5 Organelle Movement on MTs
b) Chapter – 18.4 Mitotic Spindle
c)
Media – 16.7 Kinesin: How the motor protein moves the organelles
d) Media – 16.3 Microtubule Dynamics in vivo
Intermediate Filaments
1.
Main function is to enable cells to withstand mechanical stress that occurs
when cells are stretched.
2.
“intermediate” because size is between the thin actin filaments and thicker
myosin filaments of smooth muscle.
3.
Toughest of most durable
4.
Surround nucleus and extend to periphery as well as reside in nucleus
a)
In cytoplasm, they anchor the cell membrane at cell-cell junctions
b) In nucleus, they underlie and strengthen the nuclear envelope
Intermediate Filaments (cont’d)
5.
Present in the axons of nerve cells where the long extension needs
strengthening
6.
Present in skin cells and muscle cells which constantly stretch
7.
Connect to each other from one cell to another at desmosomes, junctions
fastening cells together.
8.
Epidermolysis bullosa simplex: gene mutation causes skin cells to rupture
under gentle pressure and skin blisters
9.
Intermediates filaments must breakdown and reform during cell division
when the nuclear envelope (membrane) disappears and reforms.
Microtubules
1.
Stiff, hollow tubes of a protein, tubulin.
2.
Tubulin can be disassembled and reassembled
3.
Tracks of tubulin extend from the centrosome. Organelles, vesicles move
along these tracks which therefore controls the position of the membranebound organelles in a cell and guiding intracellular transport.
4.
MTs form the mitotic spindle or spindle that segregates the chromosomes
during cell division.
5.
MTs also form the cilia and flagella in a “9 + 2” arrangement.
6.
Free tubulin subunits exist in the cytosol.
a)
Colchicine is a drug that binds to free tubulin and prevents its
polymerization into MTs, thus no spindle assembly.
b) Taxol binds to MTs and prevents them from disassembling so they can
grow but cannot shrink. It also stops cell division.
Figure 7.24 Ultrastructure of a eukaryotic flagellum or cilium
Microtubules (cont’d)
7.
The centrosome is the major microtubule-organizing center in animal cells
8.
MTs demonstrate “dynamic instability.” This is growing and shrinking of
MTs on their own.
9.
MTs organize the interior of the cell. Growing MTs can be stabilized and
“fixed” to maintain organization with a cell.
a)
The axons of nerve cells have vesicles of neurotransmitters flowing
down them along MTs. [10 cm / day; others, a week or longer]
b) Again, this movement is associated with motor proteins.
Motor Proteins Drive Intracellular Transport
Molecular Biology of the Cell
Media – 16.7 – Kinesin: How Kinesin Works in Detail
1.
Bind to actin and MTs and use ATP hydrolysis to move along the actin or
MT filament. The other end of the motor protein is attached to a cellular
component and thus transports it and its cargo.
2.
Kinesin Family of Motor Proteins: move towards the end of the MT
a)
Kinesins attach to outside of ER membrane pull the ER membrane
outward along microtubules.
b) Colchicine causes the ER to alter location because the MTs are
disassembled. The ER collapses to the center, towards the nucleus.
3.
Dynein Family of Motor Proteins: move inward, towards the centrosome
Motor Proteins Drive Intracellular Transport (cont’d)
3.
Dynein Family of Motor Proteins: move inward, towards the centrosome
a)
4.
Dynein pulls the Golgi apparatus toward the cell center
Cilia and Flagella Contain MTs Moved by Dynein
a)
Cilia and flagella propel water over the surface of the cell
b) A cilium’s microtubules grow from a basal body in the cytoplasm.
c)
A cilium is made of a core of stable (not dynamic instability)
microtubules
d) Cilia can propel, they can move mucus in your respiratory tract, they
can move eggs through your oviducts or capture food if you were a
protozoan.
e)
Cilia move in a whiplike motion whereas flagellum generate waves
along their length.
Motor Proteins Drive Intracellular Transport (cont’d)
f)
Microtubules are arranged as doublet microtubules, nine of them.
g) These nine surround a pair of single MTs
h) Dynein generates the bending motion of the core. One end, its tail, is
attached to one MT, while the head end interacts with an adjacent MT
to produce a sliding motion that causes the cilium to bend.
Figure 7.24 Ultrastructure of a eukaryotic flagellum or cilium
Figure 7.23 A comparison of the beating of flagella and cilia
Figure 7.23x Sea urchin sperm
Figure 7.25 How dynein “walking” moves cilia and flagella
Figure 7.20 The cytoskeleton
Figure 7.21 Motor molecules and the cytoskeleton
Table 7.2 The structure and function of the cytoskeleton
Figure 7.x2 Actin
Actin Filaments are responsible for many cellular movements such as
crawling, phagocytosis or division.
1.
Actin filaments are thinner, more flexible and shorter than MTs.
2.
Actin filaments can polymerize and depolymerize such as in cell crawling
3.
Actin is found throughout the cytoplasm. Just underneath the plasma
membrane is actin that supports the outer cell surface and gives it
mechanical strength.
4.
Many cells move by crawl’n: amoeba, neutrophils migrating from the blood
into infected tissues, Linkin Park in your skin, growing tip of an axon.
5.
Integrins are transmembrane proteins in the p. membrane that adhere to a
surface on which the cell is crawling.
6.
Myosin Motor Proteins work with actin for muscle contraction
a)
First found in skeletal muscle cells
b) Myosin head moves actin filaments together to shorten muscle cells.
7.
Actin and Myosin also work in the contractile ring that pinches a dividing
cell in two by contracting and pulling inward on the p. membrane.
Figure 7.26 A structural role of microfilaments
Figure 7.27 Microfilaments and motility
Figure 7.28 Plant cell walls
Extracellular Matrix of Animal Cells
Characteristics of the ECM
1.
Secreted by the cells
2.
Made of collagen, a glycoprotein. Collagen is fibrous and makes up 50%
of protein in humans.
3.
Fibronectins connect cells to ECM
a)
Integrins, proteins in the p. membrane, are attached to the
cytoskeleton at one end and the fibronectins outside of the cell to
anchor the cell and transmit changes within the cell to ECM and vice
versa.
Figure 7.29 Extracellular matrix (ECM) of an animal cell
Intercellular Junctions
Types of Intercellular Junctions
1.
Plasmodesmata
a)
2.
Channels between plant cells for water, solutes, hormones, to pass.
Tight junctions
a)
In animal cells
b) Membranes of adjacent cells are fused
3.
Desmosomes
a)
4.
Fasten cells together in sheets
Gap Junctions
a)
Channels between cells: hormones, ions, sugars, amino acids, etc.
Figure 7.30 Intercellular junctions in animal tissues
Figure 7.22 Centrosome containing a pair of centrioles