Cell Cytoplasm

7/28/2019 Cell Cytoplasm

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Cell structure


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Cytoplasm - Substance btw cell membrane and the

membrane surrounding the nucleus. It contains:

Cytosol - intracellular fluid containing dissolvednutrients, ions, soluble, and insoluble proteins, and

waste products.

Organellesspecialized structures that perform

specific functions related cell structure, growth,

maintenance, and metabolism (except the nucleus)

Cytoskeletonnetwork of filaments and fibers.

Inclusions (storage substancesfor example, fat

droplets or glycogen)


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Organelles

Small specialized structures for particular

functions. They are divided into: Organelles of general importance are

organelles that are obligatory contents of all

cells.

Organelles of special importance are

organelles that are present in some cells (for

example, microvilli on the apical surface of

cells that are responsible for absorption, cilia

on the apical surface of columnar ciliated

cells in the respiratory system, flagellum of

spermatozoon.


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Nonmembranous organelles are notenclosed by a membrane and always in

touch with the cytosol

Cytoskeleton, microvilli, centrioles, cilia,ribosomes, flagella

Membranous organelles are surrounded by

endomembranes

Endoplasmic reticulum, Golgi apparatus,

lysosomes, peroxisomes, mitochondria

Organelles


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Cytosol

Organelles Cytoskeleton

Inclusions

Cell Cytoplasm


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Classification of the cytoplasmic

organelles

According to the modern world view the

cytoplasmic organelles are divided into:

system of synthesis: rough-surfaced

endoplasmic reticulum (rER), smooth-surfacedendoplasmic reticulum (sER), ribosomes, Golgi

apparatus.

System of energy: mitocondria.

System of intracellular digestion: lysosomes,

peroxisomes.

System of the cytoskeleton: microtubules,

microfilaments, intermediate filaments, centrioles.


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Endoplasmic Reticulum-set

of interconnected membranes.

Forms cisternae.

2 types:

Rough ER - studded with

ribosomes that are attached to

cytosolic side of rER

Smooth ER- no ribosomes

*Ribosomes formed in

nucleolus*


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The Endoplasmic Reticulum


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Endoplasmic Reticulum (ER) - system oftubes and sacs formed by membranes

Rough = modifies

proteins produced on

the ribosomes.Synthesis of proteins

for export from the

cell, integral proteins

of cell membrane,enzymes of lysosomes

Smooth = functions in

lipid synthesis (including

steroids), carbohydrate

synthesis and metabolism,

drug detoxification, and

calcium storage in musclecells


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0.5 micrometers

smooth endoplasmic reticulum

vesicles

ribosomes

rough endoplasmic reticulum

0.5 micrometers


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Rough & Smooth ER

Rough ER

Smooth ER

Ribosomes

TEM micrographs


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Ribosomes Sites of protein

synthesis

Composed of a largeand small ribosomal

subunits Contain ribosomal

RNA (rRNA) andproteins

Types

Free - movethrough thecytoplasm

Fixed (bound) -

attachedto roughendoplasmicreticulum

Free ribosomes produce proteins within the cytoplasm (forthe proper needs of the cell).


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Ribosome


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Ribosomes


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Ribosomes = site of protein synthesis; function

in the cytoplasm, but are assembled in the

nucleolusa. Free =

unbound in the

cytoplasm;

produce

proteins for use

inside the cellb. Bound =

attached to the

endoplasmic

reticulum;produce proteins

for export and

for the plasma

membrane


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The Golgi Complex Structure

series of sacs with internal spaces like RER

two faces: convex outer cis-Golgi, forming

face; concave inner trans-Golgi, maturing face)

Function

Site of protein processing

modifies, sorts and packages proteins and lipids for

shipment to appropriate location (for secretion from the

cell, enzymes for lysosomes, for the cell membrane)

transport vesicles from rER fuse with Golgi complex


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Forms secretory vesicles

Discharged by exocytosis

Forms new membrane components

Packages lysosomes

Golgi Apparatus


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Figure 3.9 The Golgi Apparatus


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Functions of the Golgi

Apparatus


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Mitochondrion/a

Powerhouse of the cell

Extracting energy from food and convertinginto a useful molecular form of energy for the

cell (ATP) Has outer and inner membranes, cristae,

matrix

Has its own DNA, RNA, ribosomes, enzymes

for lipid and protein synthesis and Krebs cycleenzymes (about 200 types of enzymes)

Requires oxygen


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Mitochondrion


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Mitochondria Provide energy for

cell Major site of ATP

synthesis

Membranes

Cristae:

Infoldings of

inner membrane

Matrix:Substance

located in space

formed by inner

membrane


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Mitochondria


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LysosomesMembrane bound

vesicles that pinchoff from Golgi

apparatus

Contain digestiveenzymes

Perform clean up

and duties


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Lysosomes

Vesicles containing hydrolytic enzymes

Digest material engulfed by cell

Digest and recycle damaged organelles(autophagy)

Waste storage (residual body)


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Lysosomes

Primary:

Contain only digestive enzymes.

Secondary:

Fused with food vacuole or organelle.

Residual body (tertiary):

Contain undigested wastes. It is normal feature

of cell aging (for example in nerve cellsage

pigment lipofuscin)


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Lysosomes

Lysosome


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Lysosome

From Krogh, Biology: A Guide to the Natural World, 2nd edit ion


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Peroxisomes

Vesicles containing the oxidase enzymes. Carryenzymes that neutralize toxins

02 + molecule + enzymes -> H202 then catalase converts H202 -> H20 + 02.

In liver and kidney cells to deal with toxicmolecules.

The Cytoskeleton: Internal


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The Cytoskeleton: Internal

ScaffoldingFunctions Cell shape, cell movement, organelle

movement, cell division, cell to cell link. Function as acells skeleton

Microtubules Structural role

Major elements for moving vesicles within cell

Movement of chromosomes during cell divisionMicrofilaments

Smallest cytoskeletal fibers

Composed of actin works with myosin for muscle contraction in muscle cells

Support structure; changes in cell shape Aids in cell movement, prey capture (pseudopodia)

Intermediate filaments (skeleton) Most permanent of cytoskeletal filaments

Stabilize nucleus and organelles within the cell

C k l


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Cytoskeleton

actin microtubulesintermediatefilaments

Extensive network of long, thin protein filaments Thinnest filaments - actin contractile machinery Thickest filaments - microtubules (minute hollow tubes)

- important for dividing cells - chromosomes Intermediate filaments - mechanical strengthening

Adapted from ECB Fig 1-20


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Cytoskeleton

Major components:

1. Microtubules (composed of

tubulin subunits)

2. Microfilaments (mostly actinand myosin)

3. Intermediate filaments

Functions: support & movement ofcellular structures & materials


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Cytoskeleton

Mi b l


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Microtubules

Primary component

of the cytoskeleton

Allow for change in

shape

Allow for movement

of vesicles ororganelles within the

cell

Assist in cell division

Formcentriolesandcillia, tail of

spermatozoon


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Microfilaments -

protein strands known

as actin

Anchor cytoskeleton

to protein of the cell

membrane.

Interact with other

proteins to determine

consistency

Interact with the

protein myosin to

produce active

movement.


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Intermediate

filamentsMake the

specificity of cells

Stabilize the

position of

organelles

Stabilize position

of the cell withrespect to

surrounding cell

Types of intermediate filaments


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Types of intermediate filaments

Filament type Cell type Examples

Cytokeratins Epithelial cell Stratified keratinized

and nonkeratinized

epithelium

Vimentin Mesenchymal cells Fibroblasts,

chondroblasts,

endothelial cells

Desmin Muscle Striated and smoothmuscle

Neurofilaments Neurons Different types of

neurons

Glial filaments Glial cells Astrocytes


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Direct the movement of chromosomes

during cell division

Organize the cytoskeleton

Cytoplasm surrounding the centrioles is the

centrosome

Centrioles

C t i l


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Centrioles

In specialized zone

near nucleus:Centrosome

Each unit consists

ofmicrotubules

Before cell

division, centrioles

divide, move to

ends of cell andbecome spindle

fibers

2 t i l


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2 centriolesdirect formation

of mitotic spindle

In 9+0 array


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Cilia Cell surface

projections Capable ofmovement

Moves materials over

the cell surface

Sensory capabilities


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Is anchored by a basal body

Beats rhythmically to move fluids across cell

surface Their movement provide the movement of

the oocyte through the oviduct, clean the

inhaled air.

Cilia

C C


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Centrioles and Cilia


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Flagella

Similar to cilia but

longer

Usually only one

exists per cell

Move the cell itself

in wavelike fashion

Example: Spermcell

Two kinds of cellular


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Two kinds of cellularextensions

Contain microtubules

Cilia

Profusion of hair-likegrowths

Move a cell or movematerial around a cell

Found in respiratorytract, oviduct

Flagella

Few (sometimes there isonly one)

Cell movement

Sperm is the onlyflagellated animal cell


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Microvilli

Extension ofplasma membrane

Increase the cell

surface Normally manyon

each cell

Form a brush

border on the

apical surface of

the cell

Do not move


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Inclusions

Are products of the vital activity of the cell.

They can be spent if there is necessary and

be accumulated. They are divided into:

Nutritious (lipid droplets, glycogen)

Pigmental (pigmental granules)

Secretory (secretory granules)

Excretory


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Cell Cytoplasm