Bio 11 - Cell Structure

7/27/2019 Bio 11 - Cell Structure

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FORMULATION OF THE CELL THEORY

In 1839, Theodor Schwann published his book on

animal and plant cells

He summarized his observations into three

conclusions about cells:

1) The cell is the unit of structure, physiology, and

organization in living things.

2) The cell retains a dual existence as a distinct entity

and a building block in the construction of organisms.

The correct interpretation of cell formation by division

was finally promoted by others and formally enunciated

in Rudolph Virchow's powerful dictum, "Omnis cellula e

cellula"... "All cells only arise from pre-existing cells".


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THE MODERN TENETS OF CELL THEORY

6. all energy flow (metabolism & biochemistry) of life

occurs within cells.

1. all known living things are made up of cells.2. the cell is structural & functional unit of all living things.

3. all cells come from pre-existing cells by division.

(Spontaneous Generation does not occur).

4. cells contains hereditary information which is passed

from cell to cell during cell division.

5. All cells are basically the same in chemical

composition.


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THE CELL : basic unit ofstructure and function

Animal

cell


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Eukaryotic and prokaryotic cells

Eukaryotic cells

subdivided by internal

membranes into

membrane-enclosed

organelles.

nucleus - Largest

organelle

Other organelles incytoplasm

Prokaryotic cells

Simples, smaller,DNA not separated

from the rest of the

cell by membrane-

bounded organelles


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prokaryoticeukaryotic

mitochondrion

Chloroplast

lysosome

Golgi complex

Nucleus with

several linear

chromosomes

Endoplasmicreticulum


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Kingdom Monera

(Prokaryotic)

Protists, fungi ,

plants, animals

(Eukaryotic)

Distinguishingfeatures of cell type

Nucleoid. Nomembrane-

bounded

nucleus

-Circular strand

of DNA

- Few cell

organelles

Nucleusbounded by a

membrane

DNA in several

linear

chromosomes

Many specialized

membrane-

bound organelles

prokaryote


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The minimum

resolution of a light

microscope is about

2 microns, the sizeof a small bacterium

Light microscopes

can magnifyeffectively to about

1,000 times the size

of the actualspecimen.

At highermagnifications, theimage blurs.

Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 7.1


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2. THE CELL


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2. THE CELL


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Sugar-phosphate

backbone Nitrogen bases

DNA molecule: composed of 2 nucleotide chains, twisted in a double helix

Nucleotide= base, sugar,

phosphate


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Flow of genetic information


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Type of protein function examples

Structural

enzymatic

Support

Accelerate chemical

rx

Silk fibers for cocoons and

web.Keratin in hair, horns,

feathers

Digestive enzymes

Storage

Defensive

Storage of amino

acids

protection

of egg white for dev of embryo.

Casein, protein of milk for baby

mammals

Antibodies that combat bacteria

Transport proteins Transport of othersubs.

Hemoglobin, transports O2 fromlungs to other parts of the body.

Other proteins transport

molecules across cell

membranes

Hormonal proteins

Receptor proteins

Coordination ofactivities

Response of cell to

chemical stimuli

Insulin, secreted by pancreashelp regulate concentration of

sugar in the blood

Receptors built into the

membrane of a nerve cell

Contractile movement Actin and myosin for muscular

movement


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Every function in the living cell depends on

proteins

Motion and locomotion depends on proteins, ex.

Muscles

Enzymes for catalysis of biochemical reactions

Structure of cells and the extracellular matrix in

which they are embedded are made of proteins

Receptors of hormones are proteins

Hemoglobin is a protein Signalling molecules are proteins

Among essential nutrients are proteins

Transcription factors that turn genes on and

off are proteins Hemoglobin is a protein

Feathers, spider webs horns are made of

proteins

Seeds are rich in proteins

Proteins


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James WatsonFrancis Crick

(1953)

Rosalind Franklin- X-ray crystallographer

made the photo that

Watson and Crick used

in deducing the double

helical structure of DNA

Heritable information carried by DNA


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Nucleotides: Basic chemical units of DNA and RNA,consist of 4 nitrogenous bases linked to a sugar which is

in turn linked to a phosphate.


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Robert Hookes simple

microscope


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The Cell theory predates other great paradigms of

biology:

Darwin's theory of evolution (1859),

Mendel's laws of inheritance (1865),

Establishment of Comparative biochemistry

(1940)

Profound revelations, led to greater understanding of

the structures and processes that make up the living

state.


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All cells are surrounded by aplasma

membrane. The semifluid substance within the

membrane is the cytosol, containing the

organelles. All cells contain chromosomes which have

genes in the form of DNA.

All cells also have ribosomes, tiny organellesthat make proteins using the instructions

contained in genes.

Prokaryotic and eukaryotic cells


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Fig. 7.4 The prokaryotic cell is much simpler in structure, lacking a nucleus and the other

membrane-enclosed organelles of the eukaryotic cell.


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Cellulose- linear chain

of covalently linked

glucose

In primary cell wall, one

cellulose polymer

has ca 6000 glucose

unitsAbout 80 celulose

m,olecules associate to

form a microfibril


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The plasma membrane functions as a selective

barrier that allows passage of oxygen, nutrients,

and wastes for the whole volume of the cell.


Fig. 7.6

Internal membranes


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A eukaryotic cell has extensive and

elaborate internal membranes, which

partition the cell into compartments.

These membranes also participate in

metabolism as many enzymes are built

into membranes.

Internal membranescompartmentalize the functions

of a eukaryotic cell


The nucleus contains a


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The nucleus contains most of the genes in aeukaryotic cell. Some genes are located in mitochondria and

chloroplasts.

The nucleus averages about 5 microns indiameter.

The nucleus is separated from the cytoplasmby a double membrane. These are separated by 20-40 nm.

Where the double membranes are fused, apore allows large macromolecules and

particles to pass through.

The nucleus contains aeukaryotic cells genetic library



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Sugar-phosphate




phosphate


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Structural

enzymatic

Support

Accelerate chemical

rx



feathers

Digestive enzymes

Storage

Defensive

Storage of amino

acids

protection



mammals






membranes

Hormonal proteins

Receptor proteins


Response of cell to

chemical stimuli


sugar in the blood




movement


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proteins


Muscles










proteins


Proteins


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The DNA of genes controls protein production indirectly

using RNA as intermediary.

Sequence of nucleotide along a gene is transcribed into

RNA.

Then translated into a specific protein with a unique shape

and function.

The entire process in which the information in a gene directs

the production of a cellular product is called Gene

expression

In translating genes into proteins, all forms of life

employ essentially the same genetic code


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James Watson

Francis Crick

(1953)


made the photo that






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Kingdom Monera Protists fungi


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Kingdom Monera

(Prokaryotic)

Protists, fungi ,

plants, animals

(Eukaryotic)

Distinguishingfeatures of cell type

Nucleoid. Nomembrane-

bounded

nucleus

-Circular strand

of DNA- Few cell

organelles

Nucleusbounded by a

membrane

DNA in several

linear

chromosomesMany specialized

membrane-

bound organelles

prokaryote

The minimum


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The minimum

resolution of a light

microscope is about

2 microns, the sizeof a small bacterium

Light microscopes

can magnifyeffectively to about

1,000 times the size

of the actualspecimen.

At highermagnifications, the

image blurs.Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 7.1

S h h t


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Sugar-phosphate




phosphate


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Structural

enzymatic

Support

Accelerate chemical

rx



feathers

Digestive enzymes

Storage

Defensive

Storage of amino

acids

protection



mammals






membranes

Hormonal proteins

Receptor proteins


Response of cell to

chemical stimuli


sugar in the blood




movement

Every function in the living cell depends on P t i


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proteins


Muscles










proteins


Proteins


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James Watson

Francis Crick

(1953)


made the photo that






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Nucleotides: B i h i l it f DNA d RNA


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Nucleus directs protein synthesis

by synthesizing mRNA

Then mRNA is transported to the

cytoplasm via the nuclear pores.

Ribosomes translate the mRNAS genetic message into the

primary structure of a specific polypeptide (polymer of linked

amino acids- which are building blocks of proteins).

DNA-RNA-PROTEIN


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DNA RNA PROTEIN


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Transcription and translation

Genes provideinstructions

for making

specific proteins

enzymes Accelerate chem rx Digestive enzymes


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structural support Insects, spiders

make web

storage Storage of amino

acid

Ovalbumin=protein

of egg white

transport Transport of other

substances

Hemoglobin-

transports oxygen

Hormonal Coordination of the

organisms activities

Insulin regulate

concentration of

sugar in the blood

Receptor Response of cell to

chemical stimuli

receptors built in

membranes


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Contractile

and motorprotein

Movement Actin and

myosin formovement

Defensive

protein

Protection

against

certainmicrooorga-

nisms

Antibodies,

combat

bacteria andviruses

Proteins Continued

n clear


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nuclear

lamina, a

network of

intermediate

filaments that

maintain the

shape of thenucleus by

mechanically

supporting thenuclear

membrane,


Fig. 7.9


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DNA

DNA and associated proteins

organized into chromatin-

appear as diffuse mass When cell prepares to divide,

chromatin fibers coil up, seen as

separate structures (chromosomes)


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nucleolus


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nucleolus

Mass of densely-stained

fibers and granules

where Ribosomal RNA

(rRNA) is synthesized

rRNA combine with

proteins from

cytoplasm to form

ribosomal subunits

Ribosomes build a cells


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Ribosomes contain rRNA and protein.

A ribosome is composed of two subunits that

combine to carry out protein synthesis.

Ribosomes build a cell sproteins


Fig. 7.10

rRNA from

nucleolus

Proteins from

cytoplasm

Combine to

form ribosomal

Subunits.

Subunits exitnuclear pores

to the cytoplasm

Cell types that synthesize large quantities of


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Cell types that synthesize large quantities of

proteins (e.g., pancreas) have large

numbers of ribosomes and prominent nuclei. free ribosomes, are suspended in the

cytosol and synthesize proteins that function

within the cytosol

bound ribosomes, are attached to the

outside of the endoplasmic reticulum. These synthesize proteins that are eitherincluded into membranes or forexport from

the cell.


Endomembrane system


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Many of the internal membranes in a eukaryotic cellare part of the endomembrane system.

are either in direct contact

or connected via transfer ofvesicles, sacs of membrane.

the membranes are even modified during life.

endomembrane system includes: the nuclear envelope,

endoplasmic reticulum,

Golgi apparatus, lysosomes,

vacuoles,

the plasma membrane.

Endomembrane system


Endomembrane system


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The endomembrane

system plays a key

role in the synthesis(and hydrolysis) of

macromolecules in

the cell.

The variouscomponents

modify

macromolecules

for their various

functions.


Fig. 7.16

ER accounts for half the


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ER accounts for half the

membranes in a eukaryotic

cell.

membranous tubules andinternal, fluid-filled spaces,

the cisternae.

ER membrane is

continuous with the nuclearenvelope and the cisternal

space of the ER is

continuous with the space

between the two

membranes of the nuclear

envelope


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There are two, regions

of ER that differ in

structure and function. Smooth ER looks

smooth because it

lacks ribosomes.

Rough ER looks rough

because ribosomes

(bound ribosomes) are

attached to the outside,including the outside of

the nuclear envelope.


Fig. 7.11


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Smooth ER are important in synthesis of


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Smooth ER are important in synthesis of

lipids, oil, phospholipids and steroids (sex

hormones of vertebrates), metabolism ofcarbohydrates.

Other enzymes in the smooth ER of theliver help detoxify drugs and poisons.

These include alcohol.


Rough ER is especially abundant in those


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g p y

cells that secrete proteins, ex. pancreatic

cells synthesize protein insulin on the ER.

As a polypeptide is synthesized by theribosome, it is threaded into the cisternal space

through a pore formed by a protein in the ER

membrane.

Many of these polypeptides are

glycoproteins, a polypeptide to which an

oligosaccharide is attached.

These secretory proteins are packaged intransport vesicles that carry them to their

next stage.


Proteins on free ribosomes in cytosol


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Proteins on free ribosomes in cytosol

Nucleus

Mitochondria

Chloroplast or peroxisomes

Proteins synthesized in bound ribosomes are transferred

into the rough ER

Proteins destined for secretion or incorporation into ER

Golgi

Lysosome

Plasma membrane

Secretory pathway- ERGolgi

Secretory

vesicles

Cell

exterior

.


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Membrane bound proteins

are synthesized directly into

the membrane.As the ER membrane

expands, parts can be

transferred as transport

vesicles to othercomponents of the

endomembrane system.


Rough ER is also a membrane

factory


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Golgi akso manufactures

Some molecules.

Pectin and other noncellulosic

molecules which are incorporated with

cellulosecto cell walls.


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After leaving ERmany transport

vesicles travel to

Golgi where

products of ER

such are proteins

are modified and

stored

and then sent to

other destinations

Vesicles form

cnd leave Golgi

carry proteins


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Golgi-flattened membranous sac

Lysosomes-digestive


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Lysosomes digestive

compartment, carry out

intracellular digestion

Lysosome digest materials

taken into the cell

Hydrolytic enzymes

In the lysosome

Lysosome digesting food


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Lysosome breaking down damaged organelles

Repository of inorganic ionsContain pigmentsvacuoles


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Contain pigments

Hold reserves of proteins stock-

piled in vacuoles

Major role in growth of plant cells ,enlarge as their vacuoles absorb

water, cells become larger with

minimal investment in new

cytoplasm

vacuoles

Raphide encased in Raphide crystals


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p

carbohydratesp y
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Prismatic crystal

druses

prismatic


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prismatic

raphide

druse

C t lith
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Cystolith


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Review organelle relationships


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Review organelle relationships

Nuclear

membrane

Vesicles from ER flow

to Golgi carrying

proteinsGolgi

pinches off

vesicles give

rise to

lysosomes,

etc.

LysosomeTransport vesicle carries protein to plasma

Membrane for secretion


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Hydrolytic

enzymes and

lysosomal

membranes

made by

rough ER,

then to Golgi.

Lysosomesarise by

budding


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CHAPTER 7

A TOUR OF THE CELL


Section E: Other Membranous Organelles

1. Mitochondria and chloroplasts are the main energy transformers of cells

2. Peroxisomes generate and degrade H2O2 in performing various metabolic

functions

1. Mitochondria and chloroplasts are the main


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Mitochondria and chloroplasts are theorganelles that convert energy to forms thatcells can use for work.

Mitochondria are the sites of cellularrespiration, generating ATP from thecatabolism of sugars, fats, and other fuels inthe presence of oxygen.

Chloroplasts, found in plants and eukaryoticalgae, are the site of photosynthesis.

They convert solar energy to chemical energyand synthesize new organic compounds from

CO and H O.

1. Mitochondria and chloroplasts are the main

energy transformers of cells


Mitochondria and chloroplasts are not part


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p p

of the endomembrane system.

Their proteins come primarily from freeribosomes in the cytosol and a few from

their own ribosomes.

Both organelles have small quantities ofDNA that direct the synthesis of the

polypeptides produced by these internal

ribosomes.

Mitochondria and chloroplasts grow and

reproduce as semiautonomous organelles.


2 THE CELL basic unit of


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2. THE CELL : basic unit ofstructure and function

Mitochondria and chloroplasts are not part


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p p

of the endomembrane system.

Their proteins come primarily from freeribosomes in the cytosol and a few from

their own ribosomes.

Both organelles have small quantities ofDNA that direct the synthesis of the

polypeptides produced by these internal

ribosomes.

Mitochondria and chloroplasts grow and

reproduce as semiautonomous organelles.



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Fig. 7.17


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Almost all eukaryotic cells have


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y

mitochondria.

There may be one very large mitochondrion or

hundreds to thousands in individual

mitochondria.

The number of mitochondria is correlated with

aerobic metabolic activity.A typical mitochondrion is 1-10 microns long.

Mitochondria are quite dynamic: moving,

changing shape, and dividing.


Mitochondria have a smooth outer


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membrane and a highly folded inner

membrane, the cristae.

This creates a fluid-filled space between them.

The cristae present ample surface area for the

enzymes that synthesize ATP.

The inner membrane encloses the

mitochondrialmatrix, a fluid-filled space

with DNA, ribosomes, and enzymes.


The chloroplast is one of several members of a

li d l f l t t t ll d


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generalized class of plant structures called

plastids.

Amyloplasts store starch in roots and tubers.

Chromoplasts store pigments for fruits and flowers.

The chloroplast produces sugar via

photosynthesis. Chloroplasts gain their color from high levels of the

green pigment chlorophyll.

Chloroplasts measure about 2 microns x 5microns and are found in leaves and other

green structures of plants and in eukaryotic

algae.Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The processes in the chloroplast are


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p p

separated from the cytosol by two

membranes.

Inside the innermost membrane is a fluid-

filled space, the stroma, in which float

membranous sacs, the thylakoids.

The stroma contains DNA, ribosomes, and

enzymes for part of photosynthesis.

The thylakoids, flattened sacs, are stacked into

grana and are critical for converting light tochemical energy.


Thylakoid-flattened sacGrana-stacks of thylakoid


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Fig. 7.18

y

Stroma-fluid filled space

Like mitochondria, chloroplasts aredynamic structures


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dynamic structures.

reproduce themselves by pinching in two.

Mitochondria and chloroplasts are mobile and move

around the cell along tracks in the cytoskeleton.


Mitochondria and chloroplast compared


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2. Peroxisomes generate and degrade H2O2 inperforming various metabolic functions


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Peroxisomes contain enzymes that transferhydrogen from various substrates to oxygen

An intermediate product of this process ishydrogen peroxide (H2O2), a poison, but theperoxisome has another enzyme that convertsH2O2 to water.

Some peroxisomes break fatty acids down tosmaller molecules that are transported tomitochondria for fuel.

Others detoxify alcohol and other harmfulcompounds.

Specialized peroxisomes, glyoxysomes,convert the fatty acids in seeds to sugars, an

easier energy and carbon source to transport.

p g


Peroxisomes are bounded by a single


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membrane.

Formed by incorporation of proteins andlipids from the cytosol.

They split in two

when they reach

a certain size.


Fig. 7.19

Peroxisomes- membrane-enclosed

(from rat liver )


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(from rat liver )Assembled from

proteins

synthesized infree ribosomes

like chloroplast

and mitochondria

Contain various

enzymes

Carry out oxid.

that produce

H2O2 hydrogen

peroxide H2O2 decomposed by Catalase to water.

In seeds: fatty acids sugars during germination


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Formed by incorporation of proteins from free ribosomes

and lipids from cytosol

1. Peroxisomes

2. Mitochondrion

3. Chloroplast Also from their own proteins synthesized in

their own ribosomes

: The cytoskeleton is a network ofCytoskeleton


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Microtubule

Microfilaments

0.25 m

y

protein filaments/ extending throughout

the cytoplasm of all eukaryotes

Structural framework for the cell

Serves as a scaffold determining shape

Resp for movement

: The cytoskeleton is a network of protein


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filaments/ fibers that organizes structures and

activities

Less rigid

Less permanent

Dynamic,continually reorganized eg. In celldivision

Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Roles of the Cytoskeleton:


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Support, Motility, and Regulation

The cytoskeleton helps to support the cell and

maintain its shape

It interacts with motor proteins to produce motility

Inside the cell, vesicles can travel along

monorails provided by the cytoskeleton


Table 6-1


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10 m 10 m 10 m

Column of tubulin dimers

Tubulin dimer

Actin subunit

25 nm

7 nm

Keratin proteins

Fibrous subunit (keratins

coiled together)

812 nm

Table 6-1a

10 m


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Column of tubulin dimers

Tubulin dimer

25 nm

Fig. 6-21

VesicleATP

Motor proteins

tt h t th

Transport membranevesicles


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Receptor for

motor protein

Microtubule

of cytoskeleton

Motor protein

(ATP powered)(a)

Microtubule Vesicles

(b)

0.25 m

attach to the

receptors on

vesicles alongmicrotubules

Motor proteins can

walk the vesicles .

Involves interaction ofmotor proteins with

cytoskeleton


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Fig. 6-23

Direction of swimming

Undulates, drives

Flagella and cilia are locomotory organelles,they are microtubules extensions that project

from cells


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5 m(a) Motion of flagella

Direction of organisms movement

Power stroke Recovery stroke

(b) Motion of cilia15 m

,

cell in same

direction

Back andforth

motion

Bending of flagella and cilia by gripping & sliding microt. Pasteach other.

Table 6-1b

10 m


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Actin subunit

7 nm


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Microfilaments that function in cellular

motility contain the protein myosin in

addition to actin

In muscle cells, thousands of actin filaments

are arranged parallel to one another

Thicker filaments composed of myosin

interdigitate with the thinner actin fibers



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Cytoplasmic streaming is a circular flow of

cytoplasm within cells

This streaming speeds distribution of

materials within the cell

In plant cells, actin-myosin interactions and

sol-gel transformations drive cytoplasmic

streaming

Video: Cytoplasmic Streaming


Table 6-1c

5 m
http://e/Documents%20and%20Settings/ATOM/My%20Documents/LBU%20Document/06_27cCytoplasmicStream_SV.mpg


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Keratin proteinsFibrous subunit (keratinscoiled together)

812 nm

Extracellular components and

ti b t ll h l


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connections between cells help

coordinate cellular activities


Cell Walls of Plants


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The cell wall is an extracellular structure that

distinguishes plant cells from animal cells

Prokaryotes, fungi, and some protists also

have cell walls

The cell wall protects the plant cell, maintains

its shape, and prevents excessive uptake of

water Plant cell walls are made of cellulose fibers

embedded in other polysaccharides and

proteinCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings


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Plant cell walls may have multiple layers:

Primary cell wall: relatively thin and flexible

Middle lamella: thin layer between primary

walls of adjacent cells

Secondary cell wall (in some cells): addedbetween the plasma membrane and the

primary cell wall

Plasmodesmata are channels betweenadjacent plant cells


Ca 80 Cellulose,molecules associate


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,

to form a microfibril


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Fig. 6-28

Secondary


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Seco da y

cell wall

Primary

cell wall

Middle

lamella

Central vacuoleCytosol

Plasma membrane

Plant cell walls

Plasmodesmata

1 m

The Extracellular Matrix (ECM) of

Animal Cells


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Animal Cells

Animal cells lack cell walls but are coveredby an elaborate extracellular matrix (ECM)

The ECM is made up of glycoproteins suchas collagen, proteoglycans, andfibronectin

ECM proteins bind to receptor proteins in

the plasma membrane called integrins


Fig. 6-30a

Collagen ProteoglycanEXTRACELLULAR FLUID


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Co age

Fibronectin

Plasmamembrane

g ycomplex

Integrins

CYTOPLASMMicro-filaments

EXTRACELLULAR FLUID

(attaches ECM

to integrins)

(embedded in

a web of

proteoglycan


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Functions of the ECM: Support Adhesion Movement Regulation


Intercellular Junctions


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Neighboring cells in tissues, organs, or organ

systems often adhere, interact, and

communicate through direct physical contact

Intercellular junctions facilitate this contact

There are several types of intercellular

junctions

Plasmodesmata

Tight junctions Desmosomes

Gap junctions


Fig. 6-28

Secondary


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y

cell wall

Primary

cell wall

Middle

lamella

Central vacuoleCytosol

Plasma membrane

Plant cell walls

Plasmodesmata

1 m

Plasmodesmata in Plant Cells


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Plasmodesmata are channels that

perforate plant cell walls

Through plasmodesmata, water and small

solutes (and sometimes proteins and RNA)

can pass from cell to cell



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Cells walls are perforated with channels


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Gap junctions


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Proteinaceous tubes that connect adjacent cells.

These tubes allow material to pass from one cell to the next withouthaving to pass through

the plasma membranes of the cells.