Chapter 4Cell Structure and

FunctionNucleolusNucleus

Nuclear envelope

Ribosome (attached)Ribosome (free)

Cell Membrane

Rough endoplasmic reticulum

Golgi apparatus

Mitochondrion

Smooth endoplasmicreticulum

Centrioles

A CELL is . . . made of MOLECULES

_______ ___________ ___________ATOMS MOLECULES ORGANELLES

WHICH IS BIGGER?

_________ > _____________ > ___________Plant cell Animal cell bacteria

Note

• The shapes shown on the last slide are merely a generic version of a plant, animal, and bacteria cell.– In other words, not all plants are shaped like a

box and animal cells circular• That is simply done to show that plants have cell

walls and animal cells do not

– Every type of cell is shaped a particular way to fit whatever its function may be

ALL LIVING THINGS ARE MADE OF CELLS

• PROKARYOTES• Lack nucleus• Lack membrane

bound organelles

• EUKARYOTES• Have nucleus• Have membrane

bound organelles

Bacterial Cell

All cells (both prokaryotic and eukaryotic) have several basic features in

common1. Plasma (cell) membrane

2. Chromosomes which carry genes made of DNA (although the shape of eukaryotic chromosomes and a prokaryotic chromosome are different)

3. Cytoplasm

4. Cytoskeleton

5. Ribosomes that make proteins (although the shape of eukaryotic ribosomes and prokaryotic ribosomes are different)

1. CELL MEMBRANE(also called plasma membrane)

Made mainly of phospholipids & proteins

Controls what enters and leaves the cell

Outsideof cell

Insideof cell(cytoplasm)

Cellmembrane

Proteins

Proteinchannel Lipid bilayer

Carbohydratechains

Cell membrane continued -PHOSPHOLIPID

• Phospholipid has 2 main regions:

• Head negative charge, hydrophilic

• 2 fatty acid Tails nonpolar, hydrophobic

HYDROPHILIC

HYDROPHOBIC

Cell membrane continued - PHOSPHOLIPID BILAYER

• They form a two-layered sheet called the phospholipid bilayer.

• Hydrophilic heads face out• Hydrophobic tails tucked inward.

• Proteins are embedded on the membrane,

or attached to the surface.

Cell membrane continued • Proteins are embedded on the membrane,

or attached to the surface.

Proteins that stick on the surface = PERIPHERAL

(either inside or outside of cell)

Proteins that stick INTO membrane = Integral(can go part way in or all the way through)

Cell membrane continued - Permeability

• Nonpolar molecules such as O2 and CO2 can easily pass through the hydrophobic interior.

• Proteins in the membrane form channels that allow specific molecules to cross.

Recognize “self”

Cell membrane continued - GLYCOPROTEINS

GLYCOPROTEINS are PROTEINS with carbohydrates attached.

Play a role in cell-cell interactions.

Cell membrane continued - TRANSPORT PROTEINShelp move substances across the cell membrane

Cell membranes MOVE!

Molecules in cell membranes are

constantly moving and changing

Cell membrane continued - WHAT DOES IT DO?

Acts as a boundaryControls what enters and leaves cell

2. Chromosomes - Genetic material (DNA)

• Chromatin – thin fibers of DNA and proteins that look like a diffuse mass.

• As the cell prepares to divide, the DNA is copied and the chromatin coils up (becoming visible with a light microscope) into the structure we know as chromosomes.

3. CYTOPLASM (Between nucleus and cell membrane)

ORGANELLE-small structure with a specific function (job)

Organelles suspended in gel-like goo

4. CYTOSKELETON

• Helps cell maintain shape• Help move organelles around

Network of protein fibers, found throughout the cytoplasm.

Three main types of fibers make up the cytoskeleton:1. Microfilaments (the thinnest)2. Microtubules (the thickest)3. Intermediate filaments (in between)

Cytoskeleton continued -Microfilaments

• Solid rods made of the protein actin, in a twisted double chain

• Supports the cell’s shape & involved in cell movement.– Ex: Actin and another protein

myosin interact to cause contraction of muscle cells.

Microfilament

Actin subunit

Cytoskeleton continued - Microtubules

• Straight hollow tubes made of the protein tubulin.

• Easily disassembled & subunits reused elsewhere.

• Give shape and support to the cell & acts as tracks along which organelles with motor proteins can move.– Ex: lysosomes move along track to

reach a food vacuole.– Ex: guide chromosomes during cell

division

• The main component of cilia & flagella

Tubulin subunit

Microtubule

Nucleus

Cytoskeleton continued - Intermediate filaments• Made of various proteins,

and has a ropelike structure.

• Reinforce cell shape & anchors organelles. – Ex: Nucleus is held in place

by a cage of intermediate filaments.

– Ex: Our outer layer of skin consists of dead cells containing intermediate filaments made of keratin proteins.

Nucleus

Intermediate filament

Characteristics of prokaryotic cells that are not found in eukaryotic cells

1. Bacterial chromosome – present as a single loop of DNA (eukaryotic chromosomes come in many pairs which we will discuss in detail later)

2. Nucleoid – region where the prokaryotic cells DNA is located (not enclosed by a membrane like eukaryotic cells)

3. Pili – attachment structures on the surface of some prokaryotes

4. Cell wall – plants (which are eukaryotic cells) also have cell walls but they are made of a different structure

5. Capsule – jellylike outer coating outside of cell wall

Note: Flagella and cilia are also found in animal cells (not plants), but they are included here because the diagram shows them. Sperm have flagella, cells in your wind pipe have cilia, and so forth.

• Flagella (long tail like structure) and cilia (many hair like structures) used for locomotion (some types of eukaryotic cells do have flagella or cilia)

Typical Prokaryotic cell

Fig. 4-3b

Nucleoid

Ribosomes

Plasma membrane

Cell wall

Capsule

Flagella

Bacterialchromosome

Pili

Nucleoid• The DNA of a prokaryotic cell is coiled into a region

called the nucleoid. • Unlike the eukaryotic nucleus, it has no membrane that

surrounds the DNA.• The DNA of a prokaryote is in a single circular loop. The

DNA of eukaryotes (like you) are in chromosome form (we’ll discuss this next unit).

• Also, the ribosomes of prokaryotic cells are smaller.• Antibiotics are designed to target (smaller) ribosomes of

prokaryotic cells (bacteria), interrupting protein synthesis. – Antibiotics do not harm eukaryotic cells.

Cilia & Flagella

• Both consist of microtubules wrapped in an extension of the cell membrane.

• Ring of 9 microtubule “doublets” surrounds a central pair of microtubules. – (called 9 + 2 pattern)

Outer microtubuledoublet

Centralmicrotubules

Plasmamembrane

• Cilia – short numerous appendages that propel cell forward.– Found on cells lining the human windpipe,

which sweeps mucus & trapped debris out of our lungs.

Cilia

• Flagella – longer, and limited to one or a few per cell.– Sperm have flagella for movement.

Flagellum

Bacteria

How did the first eukaryotic cells form?

• ENDOSYMBIOSIS

Endosymbiosis• Mitochondria & chloroplasts were formerly small

prokaryotes that began living within larger cells.• May have occurred as undigested prey or internal

parasites.• Forming symbiotic relationship.

– Host cell uses nutrients released from photosynthetic endosymbionts.

– Endosymbionts are provided protection by host cell.

• Over time, they would become more interdependent, eventually becoming a single organism.

Evidence of Endosymbiosis

• Mitochondria & chloroplasts both contain their own DNA & ribosomes.

• Their ribosomes are more similar to prokaryotic ribosomes.

• Both reproduce by a splitting process similar to that of prokaryotes.

• Both are surrounded by two membranes.

Fig. 4-16

Engulfing ofphotosyntheticprokaryote

Chloroplast

Mitochondrion

Somecells

Host cell

Mitochondrion

Host cellEngulfing of aerobicprokaryote

Organelles that are unique amongst eukaryotes (basically plants and animals) but not present in prokaryotes (bacteria)

1. Nucleus

2. Nucleolus

3. Endoplasmic reticulum

4. Golgi Apparatus (also called golgi body)

5. Mitochondria

6. Peroxisome

7. Vacuoles

1. NUCLEUS• Contains cell’s genetic material (DNA)

• Controls cell’s activity by directing protein synthesis.

• Largest organelle

in animal cells

1. NUCLEUS• Surrounded by NUCLEAR ENVELOPE • It is a double membrane perforated with

protein lined pores.

(also called NUCLEAR MEMBRANE)

1. NUCLEUS

NUCLEAR PORES • Openings that control the flow of materials into and

out of the nucleus

2. NUCLEOLUS• Dark spot in nucleus• Site where ribosomal RNA (rRNA) is synthesized

according to the instructions of DNA. • Proteins brought in through the nuclear pores are

assembled with the rRNA to build a subunit of ribosomes.

• These subunits exit through the nuclear pores where they will be joined to form functional ribosomes. Large

subunitSmallsubunit

Diagram of a ribosome

Another type of RNA• The nucleus directs protein synthesis with

messenger RNA (mRNA).

• mRNA is a short transcription (copy) of DNA that exits through the nuclear pores where it is translated by ribosomes into amino acid sequences of proteins.

RIBOSOMES for eukaryotes can be found in several places

Can be attached to:

• Nucleus

• Rough ER OR

• Free in cytoplasm

3. ENDOPLASMIC RETICULUM

Two kinds:SMOOTH or ROUGH

Network of flattened sacs and tubules

“endoplasmic” – within the cell

“reticulum” – little net

Smooth ER

• NO ribosomes attached

• Has enzymes for special tasks:

• Example: Cells of ovaries & testes synthesize the steroid sex hormones. – Enzymes synthesize lipids

• (oils, phospholipids, & steroids)

Another example (pg.60)• Liver cells help process drugs and other harmful

substances.• Cells exposed to drugs cause the amount of smooth

ER (w/ detoxifying enzymes) to increase• This increases the rate of detoxification. • Causing increasing tolerance to the drug.• Now, dose must be increased to be effective.

• Another complication is that enzymes often cannot distinguish among related drugs.

• So an increase in tolerance in one drug, may cause one in another drug.– Ex: barbiturate use can decrease effectiveness of

antibiotics.

Another example (pg.60)

• In muscle cells, smooth ER membrane pumps calcium ions into the interior of the ER.

• When a nerve signal stimulates a muscle, calcium ions rush from the smooth ER into the cytoplasm….triggering a contraction of the cell.

Rough ER

• Rough ER membrane enlarges.

• Phospholipids made by enzymes of the ER are inserted into the membrane.

• Some of this membrane is passed onto other membranes in vesicles.

Rough ER

• Ribosomes attached. (rough) • These ribosomes make

proteins, which are inserted into the ER membrane, where they are modified and transported to other organelles.

• Example: Insulin. Secreted by cells in the pancreas.

Ribosome

1

2

3

4

After leaving the ER, many transport vesicles travel to the Golgi apparatus…

Transportvesiclefrom ER

Golgi apparatusRough ER

4. GOLGI APPARATUS (BODY)• Discovered by Camillo Golgi with a light

microscope.• Confirmed later with an electron microscope.

Electron micrograph

Flattened sacs stacked on top of each other.Sacs are NOT interconnected like ER.

Number of Golgi stacks correlates with how active the cell is in secreting proteins.

GOLGI APPARATUS (BODY)• Molecular warehouse & finishing factory.• Receives & modifies products from ER.• One side is receiving dock for transport vesicles• Other side is shipping dock giving off vesicles.• “maturation model” entire sacs mature as they

move from the receiving end to the shipping end, carrying and modifying their cargo as they go.

• Exiting vesicles move

to the cell membrane for

export form the cell.

5. MitochondrionMitochondria (plural)

• cellular respiration - converts food energy into a molecule energy.

• ATP (adenosine triphosphate). – The main energy source for cellular work.

Enclosed by 2 membranes.

The inner membrane is highly folded, and contains proteins that make ATP.

The folds (cristae) increase membrane surface area, enhancing ability to produce ATP.

Has 2 internal compartments

1. Internal membrane space – narrow region between inner and outer membrane.

2. Mitochondrial matrix – contains the mitochondrial DNA, ribosomes, & enzymes.

Mitochondrion’s structure

Found in plant & animal cells!

MITOCHONDRIA

• You inherit your mitochondria from your mother!

WHAT DOES IT DO?

Converts glucose to ATP

“Powerplant of cell”

6. Peroxisome

• Vesicle that neutralizes dangerous oxygen compounds– contains catalase that breaks down H2O2

– Detoxification of alcohol

• Also breaks down fatty acids to be used as fuel.

Zellweger Syndrome • Defective genes reduce or eliminate the presence

of peroxisomes • Results in build up of iron and copper in blood

and tissue • Symptoms include an enlarged liver; facial

deformities, and neurological abnormalities such as mental retardation and seizures. 

• Most infants do not survive past the first 6 months, and usually succumb to respiratory

distress, gastrointestinal bleeding, or liver failure.

7. VACUOLES

Membrane sacs used for storage

VACUOLES• Storage space for WATER,

salts, proteins (enzymes), carbohydrates, and waste

• Maintains internal pH

•Largest structure in plant cells•Small in animal cells•No vacuoles in bacteria cells

Contractile vacuoles

• Paramecium (unicellular organism, protists)

• Collect excess water from cell, and expels it to the outside of cell.

• Without vacuole, cell fluid would become too diluted to support life, & cell would eventually swell & burst.

Nucleus

Contractilevacuoles

Food Vacuole

• capture and digestion of food particles

• Fuse with lysosomes to digest food And release nutrients.

• phagocytosis - the ingestion of particulate matter

Organelles found only in plant cells

1. Cell wall (prokaryotes also have cell walls but they’re made of different material. Animals do not have cell walls)

2. Chloroplast

3. Central Vacuole

1. CELL WALLSupports and

protects cell

Outside of cell membrane

Made of carbohydrates & proteins

Plant cell walls are mainly cellulose

2. Chloroplasts• Photosynthesizing organelles -

Use energy from sunlight to make own food (glucose)

Chloroplasts• Has an inner and outer membrane.• Inside inner membrane is a thick fluid called stroma.• Stroma contains the chloroplast DNA & ribosomes.

Chloroplasts• Thylakoids (a network of connected sacs)

are stacked inside the chloroplast.

• The stacks of thylakoids are called grana

• Grana are the solar power packs – site where green chlorophyll molecules trap solar energy.

3. Central vacuole• Found in plant cells.

• Can take up more than half the cells volume

• Holds large amounts of water, food & waste

• Plays an important role in plant structure.

• Vacuoles in flower petals contain pigments to attract insects!

Organelles found only in animal cells (not in plants or

prokaryotes)1. Centrioles

2. Lysosomes – basically the “recycling center” of the cell

– The most common hypothesis as to why plant cells do not need lysosomes is that they have a cell wall that would prevent the majority of material broken down by lysosomes in animal cells from entering plant cells

1. Centrioles

Appear during cell division to guide chromosomes apart

Centrioles

2. LYSOSOMES• Membrane bound sacs that contain digestive

enzymes.• Made by rough ER & transferred to Golgi body.

Serves as a recycling center. Damaged organelles are dismantled, releasing organic molecules for reuse.

* Found in animal cells only!

2. LYSOSOMES• Protists engulf food particles into

vacuoles…

• White blood cells ingest bacteria into vacuoles…

• Lysosomes fuse with these vacuoles and empties its digestive enzymes into them.

Plasmamembrane

LysosomeDigestiveenzymes

Food vacuole

Digestion

Lysosomal storage disease

• Lack one or more lysosomal enzymes.

• Lysosomes become engorged with undigested material.

• Example: Tay-Sachs disease

• Lipid digesting enzyme is missing

• Brain cells become impaired by accumulation of lipids.

• A child with Tay-Sachs disease will die within a few years.

Apoptosis• Programmed cell death• Lysosomes help digest

unwanted cells • Cells in developing hands and

feet creates the spaces between fingers & toes.

Apoptosis

Dead cell engulfedand digested byadjacent cell

Apoptosis plays a role in:

Embryonic developmentNormal body cell maintenance Immune system responsesCancerAIDS infectionTransplant rejection

Cell to cell communication

• The vast majority of eukaryotic organisms are multicellular

• In order to function properly, these cells must be able to communicate with one another and to transmit information back and forth

Extracellular matrix (ECM) – Present only in animals

• Helps hold cells together in tissues.

• Protects and supports the plasma membrane.

• Main component: glycoproteins (ex: collagen)

• Integers - membrane proteins that interconnects the ECM to the cytoskeleton.

Fig. 4-20

EXTRACELLULAR FLUID

Microfilaments

Collagen fiber

Connectingglycoprotein

Integrin

Plasmamembrane

Glycoproteincomplex with longpolysaccharide

CYTOPLASM

Three types of cell junctions in animal cells

• Tight junction – membranes of neighboring cells are very tightly pressed against each other.

• Prevent leakage of extracellular fluid

Tight junctions

–Example: tissue lines the digestive tract, preventing the contents from leaking into surrounding tissues.

Three types of cell junctions in animal cells

• Anchoring junction – functions like rivets, fastening cells together into strong sheets.

• Common in tissue subject to stretching or mechanical stress. – Skin & heart muscle

Anchoring junction

Three types of cell junctions in animal cells

• Gap junctions – channels that allow small molecules to flow through protein lined pores between neighboring cells. – Ex: flow of ions through gap junctions in the

cells of heart muscle coordinates their contraction.

Gap junctions

Fig. 4-21

Tight junctions

Anchoring junction

Gap junctions

Plasma membranesof adjacent cells

Extracellular matrix

Plasmodesmata – Present only in plant cells

• Channels between adjacent plant cells, form a circulatory and communication system connecting the cells in plant tissue.

• Cell membrane & cytoplasm extend through the plasmodesmata, so water and molecules can pass cell to cell.

Fig. 4-22

Vacuole

Wallsof twoadjacentplant cells

Cytoplasm

Primary cell wall

Plasma membrane

Plasmodesmata

Secondary cell wall

DIFFERENCES IN ANIMAL CELLS, PLANT CELLS, AND BACTERIA

ANIMAL CELL PLANT CELL BACTERIA

Eukaryotes Eukaryotes Prokaryotes

Cell membrane Cell membrane Cell membrane

Nuclear membrane

Nuclear membrane

NO nuclear membrane

NO cell wall Cell wall made of

CELLULOSE

Cell wall made ofPEPTIDOGLYCAN

Has ribosomes Has ribosomes Has ribosomes

DNA in multiple

chromosomes

DNA in multiple

chromosomes

DNA is a single circular ring

CYTOSKELETON

CYTOSKELETON CYTOSKELETON

Small vacuoles Really big vacuole

NO vacuoles

Has lysosomes NO lysosomes NO lysosomes

Has centrioles NO centrioles NO centrioles

Has mitochondria

Has mitochondria

No mitochondria

NO chloroplasts

Chloroplasts NO chloroplasts

SMALLER SMALL SMALLEST

USE WORDS FROM THE WORD BANKS TO COMPLETE THE VENN DIAGRAM COMPARISON

Fig. 4-4b

Smooth endoplasmicreticulum

Rough endoplasmicreticulum

CYTOSKELETON:

NUCLEUS:

Nuclear envelope

Chromosome

NucleolusRibosomes

Golgiapparatus

Plasma membrane

Mitochondrion

Peroxisome

Cell wall

Central vacuoleMicrotubule

Intermediatefilament

Microfilament

Cell wall ofadjacent cell

Chloroplast

Plasmodesmata

Fig. 4-4a

Smooth endoplasmicreticulum

Roughendoplasmicreticulum

CYTOSKELETON:

NUCLEUS:

Nuclear envelope

Chromosomes

Nucleolus

Ribosomes

Golgiapparatus

Plasma membrane

Mitochondrion

Peroxisome

Centriole

Lysosome

Microtubule

Intermediatefilament

Microfilament

Fig. 4-UN3 a.

b.

c.

d.

e.

f.

g.

h.

i.

j.

k.

l.