Tour of the Cell 1(Ch. 6)

Dead White Men Who Discovered (and were made of) Cells:

Anton Van Leeuwenhoek Robert Hooke

Where the Magic Happened

The size range of cells

Nucleus

Most bacteria

Measurements1 centimeter (cm) = 102 meter (m) = 0.4 inch

1 millimeter (mm) = 10–3 m1 micrometer (µm) = 10–3 mm = 106 m1 nanometer (nm) = 10–3 µm = 10 9 m

10 m

1 m

0.1 m

1 cm

1 mm

100 µm

10 µm

1 µm

100 nm

10 nm

1 nm

0.1 nm

Human height

Length of somenerve and

muscle cells

Chicken egg

Frog egg

Most plant andanimal cells

Mitochondrion

Smallest bacteria

Viruses

Ribosomes

Proteins

Lipids

Small molecules

Atoms

Un

aid

ed

ey

e

Lig

ht

mic

rosc

op

e

Ele

ctr

on

mic

ros

co

pe

nucleus

Most bacteria

Comparing the size of a virus, a bacterium, and an animal cell

0.25 m

Virus

Animalcell

Bacterium

Animal cell nucleus

While we’re on the topic of

size...

Why Cells Are So Small: The SA:V Ratio

Surface area increases while total volume remains constant

5

11

Total surface area (height width

number of sides number of boxes)

Total volume (height width length

number of boxes)

Surface-to-volume ratio

(surface area volume)

6

1

6

150

125

12

750

125

6

Diffusion: The movement of molecules from an area of high concentration to low concentration.

Cell FractionationAPPLICATION

Cell fractionation is used to isolate (fractionate) cell components, based on size and density.

TECHNIQUE

First, cells are homogenized in a blender tobreak them up. The resulting mixture (cell homogenate) is then centrifuged at various speeds and durations to fractionate the cellcomponents, forming a series of pellets.

Tissuecells

Homogenization

Homogenate1000 g(1000 times theforce of gravity)

10 min Differential centrifugationSupernatant poured

into next tube

20,000 g20 min

Pellet rich innuclei and

cellular debris

Pellet rich inmitochondria(and chloro-plasts if cellsare from a

plant)Pellet rich in

“microsomes”(pieces of

plasma mem-branes and

cells’ internalmembranes)

Pellet rich inribosomes

150,000 g3 hr

80,000 g60 min

RESULTS

In the original experiments, the researchers used microscopy to identify the organelles in each pellet, establishing a baseline for further experiments. In the next series of experiments, researchers used biochemical methods to determine the metabolic functions associated with each type of organelle. Researchers currently use cell fractionation to isolate particular organelles in order to study further details of their function.

Prokaryotebacteria cells

Types of cells

Eukaryoteanimal cells

- no organelles

- organelles

Eukaryoteplant cells

Why organelles?• Specialized structures

– specialized functions• Containers

– Compartments = different local environments• pH, concentration differences

– distinct & incompatible functions• lysosome & its digestive enzymes

• Membranes as sites for chemical reactions– Unique lipids & proteins – embedded enzymes & reaction centers

• chloroplasts & mitochondria

Cells gotta work to live! – make proteins

• proteins control every cell function

– make energy• for daily life• for growth

– make more cells• growth• repair• renewal

Proteins do all the work!

cellsDNA

proteins

organismRepeat after me…

Proteins do all the work!

Cell functions • Building proteins

– copy DNA– DNA -> RNA– build proteins– process proteins

• Folding, modifying–Remove amino acids–Add molecules (e.g. glycoproteins)

– address & transport proteins

Protein Synthesis• Organelles involved

– nucleus– ribosomes– endoplasmic reticulum

(ER)– Golgi apparatus– vesicles

nucleus ribosome ERGolgi

apparatusvesicles

The Protein Assembly Line

The Endomembrane System

nuclearpores

nuclearpore

nuclear envelopenucleolus

histone protein

chromosome

DNA

• Function– protects DNA

• Structure– nuclear envelope

• double membrane• membrane fused in spots to create pores

Nucleus

What kind of molecules need to

pass through?

DNA

NucleusmRNA

nuclearmembrane

smallribosomal

subunit

largeribosomal

subunit

cytoplasm

mRNA

nuclear pore

production of mRNA from DNA in nucleus

mRNA travels from nucleus to ribosome in cytoplasm through nuclear pore

1

2

Nucleolus• Function

– ribosome production• build ribosome subunits from rRNA & proteins• Ribosome assembly is completed in cytoplasm

smallsubunit

large subunit

ribosome

rRNA &proteins

nucleolus

smallsubunit

largesubunit

Ribosomes • Function

– protein production• Structure

– rRNA & protein– 2 subunits combine 0.08mm

RibosomesRough

ER

SmoothER

membrane proteins

Types of Ribosomes• Free ribosomes

– suspended in cytosol– synthesize proteins that stay in

cytosol• Bound ribosomes

– attached to endoplasmic reticulum

– synthesize proteins for export or membranes

Endoplasmic Reticulum

• Function – processes proteins– manufactures membrane– synthesis & hydrolysis of

many compounds• Structure

– membrane connected to nuclear envelope & extends throughout cell

Types of ER

rough smooth

Smooth ER function• Membrane production• Metabolic processes

– Lipid Synthesis– Glycogen hydrolysis (in liver)– Drug detoxification (in liver)

Membrane Factory

• Build new membrane– synthesize

phospholipids– ER membrane expands

• buds off & transfers to other parts of cell.

Rough ER function• Produces proteins for export out of cell

– protein secreting cells– packaged into transport vesicles for export

Which cellshave lot of rough ER?

Synthesizing proteins

cytoplasm

cisternalspace

mRNA

ribosome

membrane ofendoplasmic reticulum

polypeptide

signalsequence

ribosome

Golgi Apparatus

Which cellshave lots of Golgi?

transport vesicles

secretoryvesicles

• Function– finishes, sorts, tags & ships products

• like “UPS shipping department”

– ships products in vesicles• membrane sacs• “UPS trucks”

Golgi Apparatus

Vesicle transport

vesiclebuddingfrom roughER

fusionof vesiclewith Golgiapparatus

migratingtransportvesicle

protein

ribosome

proteins

transportvesicle

Golgiapparatus

vesicle

smooth ER

rough ER

nuclear porenucleus

ribosome

cellmembrane protein secreted

cytoplasm

The Endomembrane SystemPutting it together…

Any Questions!!

Review Questions

1.. In which cell would you expect to find the most smooth endoplasmic reticulum?A. Muscle cell in the thigh muscle of a long-distance

runnerB. Pancreatic cell that manufactures digestive

enzymesC. Macrophage (white blood cell) that engulfs

bacteriaD. Epithelial cells lining the digestive tractE. Ovarian cell that produces estrogen (a steroid

hormone)

2. In which cell would you expect to find the most bound ribosomes?A. Muscle cell in the thigh muscle of a long-distance

runnerB. Pancreatic cell that manufactures digestive

enzymesC. Macrophage (white blood cell) that engulfs

bacteriaD. Epithelial cells lining the digestive tractE. Ovarian cell that produces estrogen (a steroid

hormone)

3. Of the following, which is probably the most common route for membrane flow in the endomembrane system? A. Golgi → lysosome → ER → plasma membrane B. tonoplast → plasma membrane → nuclear envelope

→ smooth ER C. nuclear envelope → lysosome → Golgi → plasma

membrane D. rough ER → vesicles → Golgi → plasma membrane E. ER → chloroplasts → mitochondrion → cell

membrane