The Building Blocks of Life

Definition

= Three part theory about cells

1. All living things are made of cells.

Part 2 of the Theory

2. The cell is the basic structural and functional unit of life.

Part 3 of the Theory

3. All cells come from pre-existing cells.

yeast cells dividing

Cells are Us

A person contains about 100 trillion cells. That’s 100,000,000,000,000 or 1 x 1014 cells.

There are about 200 different cell types in mammals (one of us).

Cells are teeny, tiny, measuring on average about 0.002 cm (20 um) across. That’s about 1250 cells, “shoulder-to-shoulder” per inch.

nerve cell

The key to every biological problem must finally be sought in the cell, for every living organism is, or at some time has been, a cell.

Why Study Cell Biology?

The Cell Theory (review)

Cells are the basic unit of life

All Cells arise from previously existing cells

The Cell Theory (proposed independently in 1838 and 1839) is a cornerstone of biology.

Two Types of Cells

1) A prokaryotic cell

2) A eukaryotic cell

Two Fundamentally Different Cell Architectures:

Prokaryotic cells

• have no nucleus or organelles enclosed within membranes.

• All species in the domains Archaea and Eubacteria have prokaryotic cells.

Eukaryotic cells

• have a nucleus and organelles that are surrounded by membranes.

• Each organelle does a specific cell function. • All species in the Eukaryota domain (protists,

fungi, plants, and animals) have eukaryotic cells. Individual protists have only one cell, while plants and animals can have trillions of cells.

Prokaryotes vs. Eukaryotes

Size comparison??

• 1. A few types of cells are large enough to be seen by the unaided eye.

• 2. Most cells are visible only with a microscope.

•The Female Egg is the largest cell in the body, and can be seen without the aid of a microscope.

PROKARYOTES vs. EUKARYOTES: Differences

(Location)

Similarities: Common Features of ALL CELLS!

The common features of prokaryotic and eukaryotic cells are:

• 1. DNA

2. Plasma membrane (a.k.a. “cell membrane”)

• 3. Cytoplasm

• 4. Ribosomes

An idealized animal cell.

A rat liver cell (with color enhancement to show organelles).

What Do Those Parts Do?

Structure of cells

HeLa Cells

Structure of Eukaryotic Cell

Pathways of Differentiation

Relative sizes of cells and cell components

Cell replacement therapy

Prokaryotic and Eukaryotic Cellular Structure

Prokaryotic and Eukaryotic Cells

• Prokaryote comes from the Greek words for prenucleus.

• Eukaryote comes from the Greek words for true nucleus.

Prokaryotic Cells: Shapes• Average size: 0.2 –1.0 µm 2 – 8 µm• Most bacteria are monomorphic• A few are pleomorphic

Basic Shapes

• Bacillus (rod-shaped) • Coccus (spherical)• Spiral

– Spirillum– Vibrio– Spirochete

Prokaryotic & Eukaryotic Cells: An Overview

Prokaryotes

Do not have membrane surrounding their DNA

lack a nucleus Lack various internal structures bound

with phospholipid membranes Are small, ~1.0 µm in diameter Have a simple structure Composed of bacteria and archaea

Prokaryotic & Eukaryotic Cells: An Overview

Eukaryotes

Have membrane surrounding their DNA

Have a nucleus Have internal membrane-bound

organelles Are larger, 10-100 µm in diameter Have more complex structure Composed of algae, protozoa, fungi,

animals, and plants

Prokaryotic & Eukaryotic Cells: An Overview

[INSERT FIGURE 3.1]

Prokaryotic Cell Membrane

• Structure

– Referred to as phospholipid bilayer; composed of lipids and associated proteins

– Approximately half composed of proteins that act as recognition proteins, enzymes, receptors, carriers, or channels

• Integral proteins • Peripheral proteins • Glycoproteins

– Fluid mosaic model describes current understanding of membrane structure

Cell Membrane

Membranes contain a hydrophilic and hydrophobic side

Composed of many different types of proteins

Proteins in the lipid bilayer move freely within the membrane

Cell Membrane

Thin pliable lipid and protein envelope that defines a cell.

Phospholipid bilayer

Functions:

• Regulates nutrient and water intake• Regulates waste removal• Site of prokaryotic respiration• Site of prokaryotic flagella

attachment• Involved in the distribution of genetic

material during binary fission

Prokaryotic Cytoplasmic Membranes

• Function– Energy storage– Harvest light energy in

photosynthetic prokaryotes– Selectively permeable– Naturally impermeable to most

substances– Proteins allow substances to cross

membrane• Occurs by passive or active

processes– Maintain concentration and electrical

gradient• Chemicals concentrated on one

side of the membrane or the other

• Voltage exists across the membrane

Cell Membrane

Trilaminar appearance of membranes

Structure of the Plasma membrane

• Plasma Membrane

• A lipid/protein/carbohydrate complex, providing a barrier and containing transport and signaling systems.

Cell membrane - Function • The cell membrane's function, in general, revolves

around is membrane proteins. General functions include:

• Receptor proteins which allow cells to communicate,

• transport proteins regulate what enters or leaves the cell,

• and marker proteins which identify the cell

Cell membrane - Function - Regulation of transport

• Transport Proteins come in two forms: Carrier proteins are peripheral proteins which do not extend all the way through the membrane. They move specific molecules through the membrane one at a time.

Channel proteins extend through the bilipid layer. They form a pore through

the membrane that can move molecules in several ways.

• The cell membrane can also engulf structures that are much too large to fit through the pores in the membrane proteins.

• This process is known as endocytosis. • In this process the membrane itself wraps

around the particle and pinches off a vesicle inside the cell.

Structure of Cholestrol molecule

STEALTH LIPOSOMES

External Structures of Prokaryotic Cells

• Types of Glycocalyces

– Capsule• Composed of organized

repeating units of organic chemicals

• Firmly attached to cell surface• Protects cells from drying out• May prevent bacteria from

being recognized and destroyed by host

External Structures of Prokaryotic Cells

• Glycocalyces

– Gelatinous, sticky substance surrounding the outside of the cell

– Composed of polysaccharides, polypeptides, or both

Capsule

Polysaccharides or polypeptides in composition.

Surround the cell wall in some bacteria.

Function:

•Protection from phagocytosis•Osmotic barrier•Reservoir for nutrients•Virulence factor

Capsule Stain

Slime Layer

Consist of polysaccharide fibers that extend form the bacterial surface

Functions:

•Protection•Attachment•Associated with biofilms

External Structures of Prokaryotic Cells• Types of Glycocalyces

– Slime layer• Loosely attached to cell surface• Water soluble• Protects cells from drying out• Sticky layer that allows

prokaryotes to attach to surfaces

Bacterial Appendages

Flagella

Axial Filaments

Pili (Fimbriae)

Bacterial AppendagesFlagella

Structures of locomotion

Originate in the plasma membrane

In bacteria rotate like a propellar

Many different arrangements

External Structures of Prokaryotic Cells

• Flagella– Are responsible for

movement– Have long structures that

extend beyond cell surface– Are not present on all

prokaryotes

External Structures of Prokaryotic Cells

Flagella

Structure Composed of filament, hook, and

basal body Flagellin protein (filament)

deposited in a helix at the lengthening tip

Base of filament inserts into hook Basal body anchors filament and

hook to cell wall by a rod and a series of either two or four rings of integral proteins

Filament capable of rotating 360º

Bacterial Appendages Arrangements of Flagella

A.Monotrichous

B.Lophotrichous

C.Amphitrichous

D.Peritrichous

Bacterial Appendages

Axial filament (endoflagella)

Originates in the cell membrane and transverses the length of the cell in the periplasmic space.

As the endoflagella rotate to move the cell the characteristic shape is formed .

Endoflagella are associated with spirochetes.

External Structures of Prokaryotic Cells

Endoflagellum is also know as an axial filament.

Attached to the plasma embrane and transverses the entire cell.

Responsible for the spirochete morphology.

External Structures of Prokaryotic Cells

• Flagella

– Function• Rotation propels bacterium

through environment• Rotation reversible, can be

clockwise or counterclockwise• Bacteria move in response to

stimuli (taxis)– Runs – Tumbles

Bacterial Appendages

• Fimbriae and Pili– Rod-like proteinaceous

extensions

Bacterial Appendages Fimbriae

Hollow tubes that protrude from some bacteria

Compose of protein

External Structures of Prokaryotic Cells

• Fimbriae • Sticky, bristlelike projections• Used by bacteria to adhere

to one another, to hosts, and to substances in environment

• Shorter than flagella• May be hundreds per cell• Serve an important function

in biofilms• Virulence factor

External Structures of Prokaryotic Cells

• Pili– Tubules composed of pilin– Also known as conjugation pili – Longer than fimbriae but shorter

than flagella– Bacteria typically only have one or

two per cell– Mediate the transfer of DNA from

one cell to another (conjugation)

Bacterial ConjugationTransfer of plasmid DNA from a donor to a recipient.

Process strengthens the bacterial cell and alows for survival in a competitive environment.

Bacterial Inclusion Bodies

1. poly-Beta-hydroxybutyric acid - stores lipids for use in plasma membrane 2. glycogen - stores starch like polymer of sugar for energy production 3. Polyphosphate granules (metachromatic granules) - storage for

phosphates for plasma membrane and the formation of ATP from ADP. 4. Sulfur granules - stores sulfur which is necessary for the metabolic

reactions in biosynthesis.

5. Mesosome

Mesosomes - invagination of the plasma membrane that increases the surfaces area of the plasma membrane during binary fission.

The mesosome also serves as a site for the attachment and distribution of genetic material during binary fission.

Mesosome

In prokaryotic cell division, called binary fission.

A diagram of the attachment of bacterial chromosomes, indicating the possible role of the mesosome (an inward fold of the cell membrane) in ensuring the distribution of the "chromosomes" in a dividing cell.

Upon attachment to the plasma membrane, the DNA replicates and reattaches at separate points. Continued growth of the cell gradually separates the chromosomes and allocates chromosome copies to the two daughter cells.

Inclusion Bodies

6. gas vacuoles - storage of metabolic gases such as methane or hydrogen gas. The gas vacuoles help in the buoyancy of the cell and aids in it motility.

7. ribosomes - responsible for the synthesis of proteins. 8. nucleoid material - the genetic material of bacteria, which usually is balled up in

the cell. During binary fission the nucleoid material unravels within the cell in order to be copied and distributed to the daughter cells.

9. Plasmid - small fragments of self-replicating extrachromosomal DNA that codes for

the resistance to antibiotics or for the productions of a specific metabolite, i.e. toxins, pigments. These plasmids may be transferred from one bacterial cell to another by the F-pili.

Inclusion Bodies

9. Plasmid - small fragments of self-replicating extrachromosomal DNA that codes for the resistance to antibiotics or for the productions of a specific metabolite, i.e. toxins, pigments. These plasmids may be transferred from one bacterial cell to another by the F-pili.

Inclusion Bodies

These plasmids may be transferred from one bacterial cell to another by the F-pili.

Inclusion Bodies10. Endospores - a survival mechanism of certain genera of bacteria such as

Clostridium and Bacillus. The endospores are composed of a complex of dipicolinc acid and

calcium and the function of the endospore is to protect the bacterial chromosome.

The endospores are very resistant to heat, desiccation, freezing, and other physical properties such as pesticides, antibiotics, dyes, and acids.

Inclusion Bodies

The endospores may remain dormant for many years until the environment becomes suitable to sustain the life of the bacteria.

The endospore will then germinate to form an exact copy of the parent cell that produced it.

Eukaryotic Cell Walls & Cytoplasmic Membranes

• Fungi, algae, plants, and some protozoa have cell walls but no glycocalyx

• Composed of various polysaccharides– Cellulose found in plant cell walls– Fungal cell walls composed of

cellulose, chitin, and/or glucomannan

– Algal cell walls composed of cellulose, proteins, agar, carrageenan, silicates, algin, calcium carbonate, or a combination of these

Cell Walls

Three different types of cell walls and their compositions: Fungal cell walls are composed of cellulose and/or chitin. Plant cell walls are composed of cellulose. Algal cell walls are composed of cellulose, silicon, and calcium carbonate.

Plasma Membrane

Consist of a lipid bilayer and associated proteins. The Plasma Membrane of Eukaryotic cells resembles and functions in the same manner as the prokaryotic plasma membrane with the following exceptions; Contains high levels of sterols such as cholesterol. No respiratory enzymes are located in the eukaryotic plasma membrane.

Respiration occurs in the mitochondria.

External Structure of Eukaryotic Cells

• Glycocalyces

– Never as organized as prokaryotic capsules

– Help anchor animal cells to each other

– Strengthen cell surface– Provide protection against

dehydration– Function in cell-to-cell recognition

and communication

Eukaryotic Appendages

Flagella There are several different arrangements of flagella in eucaryotes. This diagram represents a biflagellated eukaryotic cell.

One of the flagella aids in movement laterally and the other aids in up and down movement.

The eukaryotic flagella move like a whip.

See Flagellar handout.

Eukaryotic Appendages

• Flagella– Function

• Do not rotate, but undulate rhythmically

Eukaryotic AppendagesCilia Similar to flagella both structurally and functionally but are much shorter and more numerous.

Cilia are found peritrichously to the cell.

Move in an undulating manner and motility by those organisms with cilia is much more rapid than those with flagella.

Intracellular Structures of Eukaryotic Organisms (organelles)

Membranous Organelles

Nucleus Often largest organelle in cell Contains most of the cell’s DNA Semi-liquid portion called

nucleoplasm One or more nucleoli present in

nucleoplasm; RNA synthesized in nucleoli

Nucleoplasm contains chromatin – masses of DNA associated with histones

Surrounded by nuclear envelope – double membrane composed of two phospholipid bilayers

Nuclear envelope contains nuclear pores

Intracellular Structures of Eukaryotic Organisms (organelles)

Nucleus - double membraned organelle that houses the genetic material of cell.

Nuclear membrane contains numerous pores through which proteins and RNA can move.

Intracellular Structures of Eukaryotic Organisms (organelles)

Membranous Organelles

Endoplasmic reticulum Netlike arrangement of flattened, hollow

tubules continuous with nuclear envelope

Functions as transport system Two forms

Smooth endoplasmic reticulum (SER) – plays role in lipid synthesis

Rough endoplasmic reticulum (RER) – ribosomes attached to its outer surface; transports proteins produced by ribosomes

Intracellular Structures of Eukaryotic Organisms (organelles)

Endoplasmic reticulum - network of cytoplasmic membranes where lipids and proteins are produced. Smooth ER - synthesis of lipids Rough ER - associated with ribosomes and is responsible for the synthesis of proteins..

Intracellular Structures of Eukaryotic Organisms (organelles)

Membranous Organelles

Golgi body Receives, processes, and

packages large molecules for export from cell

Packages molecules in secretory vesicles that fuse with cytoplasmic membrane

Composed of flattened hollow sacs surrounded by phospholipid bilayer

Not in all eukaryotic cells

Intracellular Structures of Eukaryotic Organisms (organelles)

Golgi apparatus (dictyosome) is associated with the ER.

It modifies and packages the lipids and proteins manufactured by the ER and places them in vesicles for cellular use.

Intracellular Structures of Eukaryotic Organisms (organelles)

• Membranous Organelles– Lysosomes, peroxisomes,vacuoles, and

vesicles• Store and transfer chemicals within

cells• May store nutrients in cell• Lysosomes contain catabolic

enzymes • Peroxisomes contain enzymes that

degrade poisonous wastes

Intracellular Structures of Eukaryotic Organisms (organelles)

• Membranous Organelles– Mitochondria

• Have two membranes composed of phospholipid bilayer

• Produce most of cell’s ATP• Interior matrix contains 70S

ribosomes and circular molecule of DNA

Intracellular Structures of Eukaryotic Organisms (organelles)

mitochondria - involved in the production of chemical energy in the form of ATP.

Consist of convoluted inner membrane and outer membrane. Invaginations are called cristae and contain enzymes used to synthesis ATP.

All respiratory enzymes are located in the inner membrane of the mitochondria.

Cytoplasm of Eukaryotes

• Membranous Organelles– Chloroplasts

• Light-harvesting structures found in photosynthetic eukaryotes

• Have two phospholipid bilayer membranes and DNA

• Have 70S ribosomes

• Endosymbiotic Theory– Eukaryotes formed from union of small aerobic

prokaryotes with larger anaerobic prokaryotes– smaller prokaryotes became internal parasites

• Parasites lost ability to exist independently; retained portion of DNA, ribosomes, and cytoplasmic membranes

• Larger cell became dependent on parasites for aerobic ATP production

• Aerobic prokaryotes evolved into mitochondria• Similar scenario for origin of chloroplasts

– Not universally accepted

Cytoplasm of Eukaryotes

Cytoplasm of Eukaryotes

[INSERT TABLE 3.5]

Cytoplasm of Eukaryotes

[INSERT TABLE 3.4]

Eukaryotic Cell Walls & Cytoplasmic Membranes

[INSERT TABLE 3.3]