The Cell

Cell Biology

A discipline of biology:

1. Cell structure

2. Cellular processes

3. Cell division

Tight connection with

1. Molecular biology

2. Biochemistry

1

Theodor Schwann Matthias J. Schleiden

1. All living things are composed of one or more cells

2. Cells are the basic units of structure and function in living things

Cell theory

1838, 1839

2

3. Omnis cellula e cellula

All cells are derived from cells

(by means of multiplication)

Rudolph Virchow

Cell theory

2

Germ theory

Louis Pasteur

Microorganisms are not generated from inanimate material

but rather as a result of biogenesis (from other microbes)

- The discovery that a prokaryotic cell stems from another prokaryotic cell

1860’s

3

Classification of living beings

Eubacteria

Protista

Plants Animals

Fungi

Archaebacteria

Pro

ka

ryo

te

s

Eu

karyo

te

s

I. II.

III.

5

What about the viruses? 6

Origin:

I. Simplified cells

II. Derived from the DNA of host cell

They are not living beings, since they are not

capable for independent life (cell parasites)

The origin of cells

RNA cells prokaryotic cell eukaryotic cell

RNA DNA

DNA

nucleus

cytoplasmic

DNA

7

The origin of DNA

RNA world

„DNA world”

The virus hypothesis:

- viruses discovered the DNA

8

RNA world „protein world”

9

The origin of proteins

Origin of nucleus

The arhaezoa hypothesis

Thomas

Cavalier-Smith

Origin of ER andGolgi

10

Lynn Margulis

Origin of mitochondrion

- Endosymbiotic theory

11

Lynn Margulis

Origin of chloroplast

- Endosymbiotic theory

Elysia chlorotica

A plant-animal

12

Prokaryotic cell plasmid

Spherical cells

e.g. Streptococcus

Rod-shaped cells

e.g. Escerichia coli

Spiral cells

e.g. Treponema pallidum

Prokaryotic cell

Multicellular prokaryotes

Anabaena cylindrica

photosynthesis Nitrogen fixation spore

Figure 4.7 Eukaryotic Cells (Part 1)

Animal cell

Compartmentalization

Figure 4.7 Eukaryotic Cells (Part 1)

Nucleus

Animal cell

Figure 4.7 Eukaryotic Cells (Part 1)

Mitochondrion

Animal cell

Figure 4.7 Eukaryotic Cells (Part 1)

Cytoskeleton

Animal cell

Ribosomes

Figure 4.7 Eukaryotic Cells (Part 1)

Rough ER

Animal cell

Figure 4.7 Eukaryotic Cells (Part 1)

Golgi apparatus

Animal cell

Figure 4.7 Eukaryotic Cells (Part 1)

Smooth ER

Animal cell

Extracellular space

Intracellular

space

Figure 4.7 Eukaryotic Cells (Part 1)

Cell membrane

Animal cell

bound to rough ER

Figure 4.7 Eukaryotic Cells (Part 1)

Ribosomes

Animal cell

Figure 4.7 Eukaryotic Cells (Part 1)

Centrioles

Animal cell

Plant cell

Free ribosomes

Plant cell

Nucleus

Nucleolus

Plant cell

Golgi apparatus

Plant cell

Plasmodesm

Plant cell

Chloroplast

Plant cell

Mitochondrion

Plant cell

Cell wall

Plant cell

Peroxisome

Plant cell

Cell

membrane

Plant cell

Smooth ER

Plant cell

Rough ER

Plant cell

Inclusion body

Plant cell

Animal cell – Plant cell

chloroplast

cell wall

Inclusion body

Prokaryotic cells

vs. eukaryotic cells

Prokaryotic cell

Eukaryotic (animal) cell

Differences

Only in eukaryotes:

1. Cell nucleus

2. Membrane-bound organelles

Only in prokaryotes

1. Proteoglycan cell wall

2. Capsule

Cell membrane

1. Separation – selective transport

2. Communication

Cell membrane

- fluid mosaic model

Protein molecules

Phospholipid

molecules

Phospholipid

molecule

Protein

lip

id

do

ub

le

la

ye

r

1.

1.

1.

2.

3.

Phospholipids

Cholesterol:

decreases fluidity

phosphatidyl choline

Glycocalyx

glycocalyx cytoplasm nucleus cell membrane

22

Membrane microdomains

- lipid rafts

phospholipids and membrane proteins are not randomly distributed in cell membranes

Nucleoplasm

Outer membrane

Inner membrane

Nucleolus

Pore

Nuclear membrane

Nuclear lamina

Chromatin

Nucleus

inner outer

Nuclear membrane

ER membrane

ER lumen

Nuklear lamina

Nuclear pore

perinuclear space

protein

RNA

importin exportin

protein

protein

NLS: nuclear localization signal

NES: nuclear export signal Signal peptides

Nuclear membrane

Chromosomes

Giemsa staining

Human: haploid chromosome set

Chromatin

Metaphase chromosome

Solid form

Relaxed form

DNA and nucleosomes

DNA and nucleosomes

DNA

DNA

Histone H1

8 histone core

8 histone core

NUCLEOSOME

DNA H1

H3

H4

H2A

H2B

Ribosomes

Ribosomes are complexes of proteins and RNA molecules. They carry out

the synthesis of proteins. Soluble proteins are synthesized by cytoplasmic

ribosomes, while membrane and exported proteins are produced by

ribosomes of the rough endoplasmic reticulum.

30S subunit

Proteins: blue

RNAs: orange

Endoplasmic reticulum

Rough ER Smooth ER

ribosomes

Rough ER

Smooth ER

FUNCTION

1. Lysosomal enzymes

2. Secreted proteins

3. Trans-membrane proteins

4. Glycosylation

1. Lipid and steroid synthesis

2. Carbohydrate metabolism

3. Calcium storage

4. etc.

Protein maturation

in the rough ER

Golgi apparatus

FUNCTION:

1. Proteins and lipids

(a) chemical modification (glycosylation and phosphorylation)

(b) packaging and

(c) sorting

2. Carbohydrate synthesis

3. Proteoglycan synthesis

Transport vesicles

incoming (from ER)

outgoing

cisterns

Inside of cell

Outside of cell Plasma membrane

Golgi apparatus

medial

region

cis region

Proteins for use

within the cell

Proteins for use

outside the cell

trans

region

Golgi apparatus

Rough endoplasmic reticulum

Nucleus

Peroxysomes, lysosomes

peroxysome

lysososome

Acidic vesicles full of enzymes (they digest:

proteins, nucleic acids, lipids, polysaccharides)

- Small membrane vesicles, containing enzymes

that degrade peroxides and free radicals

- Metabolism of fatty acids

- Enzymes of the peroxisomes are found in

crystalline form

Inside of cell

Outside of cell

Plasma membrane

Food particles

taken in by

phagocytosis

Phagosome

Primary

lysosome

Secondary

lysosome

Lysosomes

Proteasomes

Proteasomes are enzyme complexes degrading proteins

Proteins are degraded for several reasons:

- misfolded (abnormal) proteins are destroyed

- some proteins are made only for short periods of time

- enzymes, regulatory proteins are degraded, when not needed

- when cells are starving for amino acids

There are labels (ubiquitin peptide), which identify protein molecules to be degraded.

lysosome

Mitochondrion

matrix

inner membrane

outer membrane

Inter-membrane space

Chloroplast

Granum

- stacks of thylakoids

Chloroplast

Cytoskeleton

Microfilaments

Intermediate filament

Microtubule

Cytoskeleton

rough ER

1. Maintains cell shape

2. Provides for various types of cell movement

3. Helps move things within the cell

Cytoskeleton

Microfilament

Intermediate filament Microtubules

cell membrane

rough ER

Actin monomer

Microfilaments

• Made up of strands of the protein actin and often interact with strands of other proteins

• They change cell shape and drive cellular motion, including contraction, cytoplasmic streaming, and the

“pinched” shape changes that occur during cell division

• Microfilaments and myosin strands together drive muscle action

Fibrous subunit

Intermediate filaments

• Made up of fibrous proteins organized into tough, ropelike assemblages that stabilize a cell’s structure

and help maintain its shape

• Some intermediate filaments help to hold neighboring cells together

• Others make up the nuclear lamina

• Long, hollow cylinders made up of many molecules of the protein tubulin.

Tubulin consists of two subunits, a-tubulin and b-tubulin

• Microtubules lengthen or shorten by adding or subtracting tubulin dimers

• Microtubule shortening moves chromosomes

• Interactions between microtubules drive the movement of cells

• Microtubules serve as “tracks” for the movement of vesicles

Tubulin dimer

b-Tubulin

monomer

a-Tubulin

monomer

Microtubules

Cytoskeleton

- Cell division