A Tour of the Cell - AP Biology...A Tour of the Cell m Ch. 6 Figure 6.32 Cell Types...

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A Tour of the Cell

Figure 6.32

Cell Types

Eukaryotic:

- internal membranes that

compartmentalize their

functions

- True nucleus

- Larger in size

Prokaryotic:

- Do not contain a nucleus

- Have their DNA located in

an area called the

nucleoid region

Common:

- bound by a plasma membrane

- semifluid substance called the cytosol

- contain chromosomes

- all have ribosomes

0.25 m

Animal

Bacterium

Animal cell nucleus

Cell Size

The logistics of carrying out cellular

metabolism sets limits on the size of

A smaller cell has a higher surface to

volume ratio, which facilitates the

exchange of materials into and out of the

Surface Area to Volume RatioSurface area increases while

total volume remains constant

Total surface area

(height width

number of sides

number of boxes)

Total volume

(height width length

number of boxes)

Surface-to-volume

(surface area volume)

Cell Parts

Nucleus Mitochondria

Nucleolus Chloroplast

Endomembrane System Cytoskeleton

Endoplasmic Reticulum Cell Membrane

Golgi Apparatus Extracellular Matrix

Lysosomes

Vesicles

Nucleusmembrane bound structure that contains

most of the DNA in the cellNucleus

NucleusNucleolus

Chromatin

Nuclear envelope:Inner membraneOuter membrane

Nuclear pore

Rough ER

complex

Surface of nuclear

envelope.

Pore complexes (TEM). Nuclear lamina (TEM).

Close-up of

nuclear

envelope

Ribosome

0.25 µm

Nucleus Composition

1) - enclosed in a nuclear envelope which is a

phospholipid bilayer

- each side of the layer has specific proteinsembedded in the layer

- inside layer has protein filaments nuclear lamina - gives shape to nucleus

- envelope has sections where the bilayer pinches in forming pores that are surrounded by 8 protein granules

- pore regulates the flow of materials into and out of the nucleus

Flow in: ATP, nucleotides, enzymes

Flow out: ADP, PO4-3, ribosomes, RNA

Nuclear Contents

2) DNA

- organized into loose strands called chromatin

- mixed with proteins called histones

- controls DNA expression

- Condenses to form chromosomes(colored bodies)

- each species has a specific numberwith a specific gene sequence

Nuclear Contents

3) Nucleolus:

- concentration of proteins and RNA

- site of ribosome production

- produces ribosomal subunits (parts)

which are assembled in the cytoplasm

after they leave the nucleus via the

nuclear pore

NUCLEAR CONTROL of cell

DNA RNA (mRNA, tRNA or rRNA)

PROTEINS

RIBOSOMES: site of protein synthesis

COMPOSITION: RNA and Proteins

formed into subunits assembled in nucleolus

Two types: Large and Small

put together in cytoplasm

Purpose: protein synthesis

occurs in cytoplasm

cytosolic ribosomes - make proteins needed in the cytosol

bound ribosomes - make proteins needed for cellular structure or for export from the cell

ribosomes in prokaryotes are structurally different

Importance: Targeted by antibiotics

Ribosomes Cytosol

Free ribosomes

Bound ribosomes

subunit

TEM showing ER and ribosomes Diagram of a ribosome

0.5 µm

THE ENDOMEMBRANE SYSTEM

System of tubes and vesicles that form a network

of communication and productivity in the cell -

assembly line of the cell

Membranes are related directly by contact or

by vesicles (sac enclosed by a membrane) that

pinches off one membrane and carries materials

to the next

different membranes of the system have

different compositions for different functions

Flow of the Endomembrane System

nuclear envelope

endoplasmic reticulum (E.R.)

smooth and rough (bound ribosomes)

Golgi Apparatus

Lysosomes and Vesicles

Plasma membrane expands

by fusion of vesicles; proteins

are secreted from cell

Transport vesicle carries

proteins to plasma

membrane for secretion

Lysosome available

for fusion with another

vesicle for digestion

Nuclear envelope is

connected to rough ER,

which is also continuous

with smooth ER

Nucleus

Rough ER

Smooth ERcis Golgi

trans Golgi

Membranes and proteins

produced by the ER flow in

the form of transport vesicles

to the Golgi Nuclear envelop

Golgi pinches off transport

Vesicles and other vesicles

that give rise to lysosomes and

Vacuoles

Plasma

membrane

ENDOPLASMIC RETICULUM

reticulum - network

endoplasmic - within the cytoplasm

network of tubes and cisternae

Cisternae: sacs - swollen portions at the

ends of the networks – pinch off to form

vesicles

connects to the nuclear envelope

Cisternae

TYPES OF ER

Smooth - no ribosomes bound to the outside of the

membrane

Function:

1. synthesis of lipids, phospholipids and steroids

2. carbohydrate metabolism - glycogen to glucose

3. detoxification - especially plentiful in liver

adds a carboxyl group to poisons so they are soluble

and can be excreted from the body

4. stores Ca+2 for muscle contraction

- pumps Ca+2 from cytosol into inside of ER - nerve

impulse releases the Ca+2 causing the muscle

contraction

Smooth ER

Rough ER

ER lumen

Cisternae

Ribosomes

Transport vesicle

Smooth ER

Transitional ER

Rough ER200 µm

Nuclear

envelope

TYPES OF ER

Rough - ribosomes attached to the outside of the membrane

Function:

1. Protein synthesis

- makes secretory proteins and lysosomal proteins

- manufactured by ribosomes

- move into ER via pores

- may add a sugar unit (oligosaccharide) to protein

- moves into a transport vesicle for secretion or further modification by Golgi

Role of Signal Recognition Proteins

Function of Rough ER

2. Formation of new ER

ribosomes make proteins which get imbedded

directly into the membrane - anchored by

hydrophobic regions of the protein

proteins in membrane manufacture new

phospholipids from materials in the cytosol

new portions can pinch off and go to other

portions of the cell

GOLGI APPARATUS

series of flattened membrane sacs that accept, modify and ship out proteins

CIS end - receiving end - accepts vesicles

- as proteins pass through the sacs they are modified

TRANS end - shipping end

Each section contains different enzymes that perform different modifications on the proteins

cis face

(“receiving” side of

Golgi apparatus)

Vesicles move

from ER to GolgiVesicles also

transport certain

proteins back to ER

Vesicles coalesce to

form new cis Golgi cisternae

Cisternal

maturation:

Golgi cisternae

move in a cis-

to-trans

direction

Vesicles form and

leave Golgi, carrying

specific proteins to

other locations or to

the plasma mem-

brane for secretion

Vesicles transport specific

proteins backward to newer

Golgi cisternae

Cisternae

trans face

(“shipping” side of

Golgi apparatus)

0.1 0 µm1

GOLGI APPARATUS

Products:

altered phospholipids

Components of the extracellular matrix

sorted products for secretion

LYSOSOMES

membrane sac filled with digestive

(hydrolytic enzymes)

optimal pH of 5 - maintains an internal

environment that keeps these important

enzymes from digesting the cell

helps maintain pH of cell by pumping

excess H+ into lysosome and out of

cytosol

LYSOSOMES

hydrolytic enzymes formed by ER - not yet active

passed to GOLGI where they are modified and sorted

stored and pinch off from Golgi forming lysosome

fuse with incoming vesicle filled with macromolecules for intracellular digestion

also break down old organelles for recycling of nutrients autophagy

Participate in one mechanism of apoptosis

(a) Phagocytosis: lysosome digesting food

Lysosome contains

active hydrolytic

enzymes

Food vacuole

fuses with

lysosome

Hydrolytic

enzymes digest

food particles

Digestion

Food vacuole

Plasma membraneLysosome

Digestive

enzymes

Lysosome

Nucleus

(b) Autophagy: lysosome breaking down damaged organelle

Lysosome containing

two damaged organelles1 µ m

Mitochondrion

fragment

Peroxisome

fragment

Lysosome fuses with

vesicle containing

damaged organelle

Hydrolytic enzymes

digest organelle

components

Vesicle containing

damaged mitochondrion

Digestion

Lysosome

CELLULAR SUICIDE

- Programmed Cell Death

APOPTOSIS

lysosomes release cathepsin

protease enzyme

breaks apart mitochondria which releases a

protein called cytochrome c which cause the

inside of the cell to break apart

Importance of Apoptosis

- destroys dysfunctional cells

- destroyed cells are disposed of by white

blood cells

- development of tissues

- Separates fingers and toes

- Lack of separation = syndactyly

- Break down of tissues in metamorphosis

of larvae into butterflies

Apoptosis Blebbing

Apoptosis Details Video

DISFUNCTIONAL LYSOSOMES

Tay-Sachs Disease

VACUOLES

membranous sac - larger than a vesicle

Food Vacuole - formed by phagocytosis

- meets with lysosome

Contractile Vacuole - takes in excess water for expulsion - maintains proper water concentration in cell

Central Vacuole- large main vacuole of plants

TONOPLAST - enclosing membrane of central vacuole

Central Vacuole Functions

stores wastes, ions, pigments and

minerals

stores water providing structure

may contain poisons or deterrents

Central vacuole

Cytosol

Tonoplast

Central

vacuoleNucleus

Cell wall

Chloroplast

NON - ENDOMEMBRANE SYSTEM

ORGANELLES

Peroxisomes: remove Hydrogens from substances and transfer it to Oxygen making H2O2

break down fatty acids

detoxify alcohol

Contains catylase (peroxidase) to break

H2O2 into H2O and O2

keeps the H2O2 from interacting with the rest of the cell

Chloroplast

Peroxisome

Mitochondrion

Peroxisomes

Special Peroxisomes in seeds

(glyoxysomes) break down the fatty acids

in seeds into acetyl-CoA so the seedling

has a food source

Acetyl-CoA is the main source of energy

for the Kreb’s cycle in cellular respiration

NON - ENDOMEMRANE SYSTEM

ORGANELLES

DOUBLE MEMBRANE ORGANELLES:

one membrane in the other - organelle

with two distinct spaces on the inside

MITOCHONDRIA AND CHLOROPLASTS

have their own DNA and replicate on their own

make their own ribosomes

Endosymbiotic Theory

QUESTION OF EVOLUTION???

- how did the eukaryote come about?

Formation of the nuclear membrane

- in folding of the plasma membrane

ENDOSYMBIOTIC THEORY: Page 524

2 prokaryotes - one much smaller than the other

- smaller one has the ability to carry out aerobic metabolism

- enters the larger cell by phagocytosis and does not die

- aids in host cell’s life cycle

- same happened to chloroplasts (although suspected later)

Supporting information

- both have own DNA - circular - no histones

- have a double membrane - second comes from the in folding plasma membrane of the host

- mitochondria and chloroplasts same size as prokaryotes

- similar enzymes and membranes as prokaryotes

- chloroplasts make all own enzymes

- most proteins for mitochondria are found in the genome of the nucleus - transposones?

The Endosymbiotic Theory

ORGANELLES

Mitochondria:

site of cellular respiration - particularly the Kreb’s Cycle and the Electron Transport Chain

- in almost all eukaryotes

Structure

Outer membrane

Inner membrane - Electron transport chain - houses ATP synthase

Cristae - folds that increase surface area

Intermembrane space

Matrix - Kreb’s Cycle

Mitochondrion

Intermembrane space

membrane

ribosomes

in the

mitochondrial

matrix

Mitochondrial

membrane

Cristae

Matrix

100 µm

ORGANELLES

Chloroplasts: - Photosynthesis

double membrane with internal flattened sacs

Structure

Outer and inner membrane

Stroma

Grana - stacks of thylakoids

contain chlorophyll for photosynthesis

Chloroplast

Ribosomes

Stroma

Inner and outer

membranes

Thylakoid

Granum

The Cytoskeleton

fibers and tubes extending through the

cytoplasm that organize the structures and

activities of the cellMicrotubule

0.25 µm MicrofilamentsFigure 6.20

Functions of Cytoskeleton

1) Support - internal framework - keeps the cell from expanding or being squished -maintains shape

2) Anchors organelles and enzymes for reactions

Functions of Cytoskeleton

3) Movement:

Changes in location: cilia and flagellaMovement of cell parts and organelles

contraction of protein fibers

organelle monorails

manipulation of cytoskeleton

4) Stimulation of cellular activitiesshock wave trigger - stimulation of the cell

membrane causes the fibers in the cell to move organelles causing them to activate

Organelle Monorail

VesicleATP

Receptor for

motor protein

Motor protein

(ATP powered)

Microtubule

of cytoskeleton

(a) Motor proteins that attach to receptors on organelles can “walk”

the organelles along microtubules or, in some cases, microfilaments.

Microtubule Vesicles 0.25 µm

(b) Vesicles containing neurotransmitters migrate to the tips of nerve cell

axons via the mechanism in (a). In this SEM of a squid giant axon, two

vesicles can be seen moving along a microtubule. (A separate part of the

experiment provided the evidence that they were in fact moving.)Figure 6.21 A, B

Three Main Fiber-Types of

Cytoskeleton

Microtubules

Microfilaments

Intermediate filaments

Table 6.1

Microtubules Microfilaments Intermediate

Largest Smallest Middle

Straight hollow Solid and thin Super coiled filaments

Tubulin Actin Various types of Keratin

Microtubules

shape and support

movement:

Monorail

separation of chromosomescentrioles and centrosomes

cilia and flagella

Anatomy of Centrosome

Organizational center of microtubules for

cellular division (spindle fibers)

Composed of two sets of tubes called the

centrioles

9 sets of three connected tubes

In animal cells, not plant

Centrosome

Microtubule

Centrioles

0.25 µm

Longitudinal section

of one centrioleMicrotubules Cross section

of the other centrioleFigure 6.22

Cilia and Flagella

Anatomy:

Base of Structure: same as a centriole -

imbedded in the cell membrane

“9 + 2” configuration

9 sets of two interconnected pairs + 2 central

microtubules imbedded in radial spokes

interconnected pairs are linked by protein

motor molecules called dynein

Anatomy of Cilia and Flagella

Outer microtubule

doublet

Dynein arms

Central

microtubule

Outer doublets

cross-linking

proteins inside

Radial

Plasma

membrane

Microtubules

Plasma

membrane

Basal body

0.5 µm

0.1 µm

Cross section of basal body

Triplet

Figure 6.24 A-C

Anatomy of Cilia and Flagella

Functions: move cells or move liquids

across tissues

#’s per cell

cilia - numerous

flagella - 1 - 8

Physiology of Cilia and Flagella

Movement cilia - oars - power stroke and a recovery stroke

flagella - undulating whip

motor molecules - dynein of one tubule grasps the neighboring tubule and pulls itself along so the tubules slide past one another - like shimmying across a log

extent of movement is limited by the radial spokes and membranal anchor - continued movement of the dynein molecules causes the structure to bend

Microtubule

doublets ATP

Dynein arm

Powered by ATP, the dynein arms of one microtubule doublet

grip the adjacent doublet, push it up, release, and then grip again.

If the two microtubule doublets were not attached, they would slide

relative to each other.

Figure 6.25 A

Outer doublets

cross-linking

proteins

Anchorage

in cell

In a cilium or flagellum, two adjacent doublets cannot slide far because

they are physically restrained by proteins, so they bend. (Only two of

the nine outer doublets in Figure 6.24b are shown here.)

(a) Motion of flagella. A flagellum

usually undulates, its snakelike

motion driving a cell in the same

direction as the axis of the

flagellum. Propulsion of a human

sperm cell is an example of

flagellate locomotion (LM).

Direction of swimming

(b) Motion of cilia. Cilia have a back-

and-forth motion that moves the

cell in a direction perpendicular

to the axis of the cilium. A dense

nap of cilia, beating at a rate of

about 40 to 60 strokes a second,

covers this Colpidium, a

freshwater protozoan (SEM).

Figure 6.23 B

Cilia and Flagella Video and

Animation

Cilia and Flagella Movement

Ciliophorans (paramecia)

Microfilaments

network of filaments - makes the outer

portion of the cytoplasm more gel-like and

the inner portion of the cell more fluid

movement:

muscle contraction

amoeboid movement

Anatomy of MicrofilamentsACTIN

twisted double chain of actin (globular protein) subunits

Physiology of Microfilament:

Pulling and sliding

Muscle contraction:

actin filaments are grabbed by myosin (thicker

protein filaments) and pulled - makes the muscle

fiber shorten

Actin filament

Myosin filament

Myosin motors in muscle cell contraction. (a)

Muscle cell

Myosin arm

Figure 6.27 A

Muscles

Vertebrate Skeletal Muscle:

Muscle muscle fiber(muscle cell)

myofibril sarcomere Sarcomere Structure:

Sarcoplasmic reticulum (SR)

Actin (thin filaments) and Myosin (thick filaments) organized into bands

Light – I band - (actin)

Dark – A band - (actin and myosin)

Muscle

Bundle of

muscle fibers

Single muscle fiber

(cell)

Plasma membrane

Myofibril

band Dark band

Z line

Sarcomere

TEM 0.5 m

I band A band I band

M line

filaments

(myosin)

filaments

(actin)

H zone

Sarcomere

Z lineZ line

Nuclei

Muscle Contraction:

Sliding Filament Model

1. Nerve signal from brain – motor neuron

2. Release of acetylcholine

(neurotransmitter) – intercellular

communication

3. Binds to surface of muscle cell (effector

4. Causes the release of Ca++ ions from

5. Ca++ ions bind to receptor sites on

troponin complex on the tropomyosin

on the actin filament

6. Opens the actin filament up for the myosin “head” to bind after a phosphorulated conformational change

7. The myosin is dephosphorylated and the head moves pulling the actin filament

ATP Source: creatine phosphate and glycogen

Thick filament

Thin filaments

Thin filament

ADPADP

P i P i

Cross-bridge

Myosin head (low-

energy configuration)

Myosin head (high-

Myosin head (low-

Thin filament moves

toward center of sarcomere.

filamentActin

Cross-bridge

binding site

7. Loss of Ca++ ions causes tropomyosin to

cover the actin sites and the contraction

stops – when Ca++ is pumped back into

K+ is needed to help pump Ca++ into

the SR

Synaptic

terminal

of motor

neuron

Synaptic cleft T TUBULEPLASMA MEMBRANE

CYTOSOL

Cytosolic Ca2+ is

removed by active

transport into

SR after action

potential ends.

Figure 49.33

Acetylcholine (ACh) released by synaptic terminal diffuses across synaptic

cleft and binds to receptor proteins on muscle fiber’s plasma membrane,

triggering an action potential in muscle fiber.

Action potential is propa-

gated along plasma

membrane and down

T tubules.

Action potential

triggers Ca2+

release from sarco-

plasmic reticulum

Myosin cross-bridges alternately attach

to actin and detach, pulling actin

filaments toward center of sarcomere;

ATP powers sliding of filaments.

Calcium ions bind to troponin;

troponin changes shape,

removing blocking action

of tropomyosin; myosin-binding

sites exposed.

Tropomyosin blockage of myosin-

binding sites is restored; contraction

ends, and muscle fiber relaxes.

Muscle Contraction Video

Muscle Contraction Video #2

Psuedopods:

actin near cell membrane form

microfilaments which form a network

causing the cytoplasm to become gel-like

this puts pressure on the remaining

cytoplasm pushing it in the direction where the

gel network did not form - like squeezing a

tube of toothpaste Cortex (outer cytoplasm):

gel with actin network

Inner cytoplasm: sol

with actin subunits

Extending

pseudopodium

(b) Amoeboid movement

Amoeboid

Movement

Amoeba eating

More fat

Amoeba

Cytoplasmic Streaming

Nonmoving

cytoplasm (gel)

Chloroplast

Streaming

cytoplasm

Parallel actin

filamentsCell wall

(b) Cytoplasmic streaming in plant cells

Cytoplasmic Streaming in Elodea - Video

Intermediate Filaments

maintain internal structure and support real cellular skeleton

holds nucleus in place and make up nuclear lamina

Anatomy: rope like structures - tightly twisted strands of keratin

proteins

Physiology:determine cell shape and therefore function

Intermediate Filaments

Cell Surfaces and Junctions

Plant cell walls:

1st layer: middle lamella - sticky polysaccharides

2nd layer: primary wall - cellulose

- 1st and 2nd in all plant cells - herbaceous

3rd layer: secondary wall - cellulose

continues to grow inward - can eventually kill the cell

adding a protein called lignin = wood

Communication between plant cells

plasmodesmata - thin tubes connecting cell membranes

Central

vacuole

of cell

Plasma

membrane

Secondary

cell wall

Primary

cell wall

Middle

lamella

Central

vacuole

of cell

Central vacuole

Cytosol

Plasma membrane

Plant cell walls

PlasmodesmataFigure 6.28

Plasmodesmata

Interior

of cell

Interior

of cell

0.5 µm Plasmodesmata Plasma membranes

Cell walls

Figure 6.30

Animal Cell Surfaces and Junctions

Functions of the Junctions:

hold the cell membranes together

communication between cells

Types of Junctions

Tight Junctions: proteins that hold cell membranes together to keep the intercellular fluid (fluid between cells) from leaking out - clips

Desmosomes: protein anchors - bind cells together - reinforced by intermediate filaments -roots anchoring a tree

Gap junctions: protein channels - tunnels that connect cell membranes and allow materials to pass through the cells - similar to plasmodesmata

Tight junctions prevent

fluid from moving

across a layer of cells

Tight junction

0.5 µm

between

cellsPlasma membranes

of adjacent cells

Extracellular

matrix

Gap junction

Tight junctions

0.1 µm

Intermediate

filaments

Desmosome

junctions

At tight junctions, the membranes of

neighboring cells are very tightly pressed

against each other, bound together by

specific proteins (purple). Forming continu-

ous seals around the cells, tight junctions

prevent leakage of extracellular fluid across

A layer of epithelial cells.

Desmosomes (also called anchoring

junctions) function like rivets, fastening cells

Together into strong sheets. Intermediate

Filaments made of sturdy keratin proteins

Anchor desmosomes in the cytoplasm.

Gap junctions (also called communicating

junctions) provide cytoplasmic channels from

one cell to an adjacent cell. Gap junctions

consist of special membrane proteins that

surround a pore through which ions, sugars,

amino acids, and other small molecules may

pass. Gap junctions are necessary for commu-

nication between cells in many types of tissues,

including heart muscle and animal embryos.

TIGHT JUNCTIONS

DESMOSOMES

GAP JUNCTIONS

Figure 6.31

Extracellular Matrix

goop on the surface

differs from cell to cell based on function

General Composition:

glycoproteins: proteins with an oligosaccharide: collagen - forms strong fibers outside of cell -

proteoglycans - proteins that have very large sugar complexes attached to them - sticky

fibronectins - adhesive protein attached to membrane proteins called integrins (bound to microfilaments in cytoskeleton)

results in the chemical and mechanical stimulation of the cell from external stimuli

Extracellular Matrix

Collagen

Fibronectin

Plasma

membrane

EXTRACELLULAR FLUID

Micro-

filaments

CYTOPLASM

Integrins

Polysaccharide

molecule

Carbo-

hydrates

Proteoglycan

molecule

protein

Integrin

Figure 6.29

A proteoglycan

complex

Inside the Cell

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A Tour of the Cell - AP Biology...A Tour of the Cell m Ch. 6 Figure 6.32 Cell Types...

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