Chapter 3 Cell Structure and Function - Brazosport...

Chapter 3 Cell Structure and Function

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Processes of Life

What is the difference between a living thing and a

non-living thing?

What are the processes of life?

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Figure 3.1 Examples of types of cells.

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How are these cells similar?


Prokaryote Eukaryote

Prokaryotic and Eukaryotic Cells: An Overview

• Tell Me Why

• In 1985, an Israeli scientist discovered a

single-celled microbe, Epulopiscium

fishelsoni. This organism is visible with

the naked eye. Why did the scientist think

Epulopiscium was eukaryotic?

• What discovery revealed that the microbe

is really a giant bacterium?


External Structures of Bacterial Cells

• Two Types of Glycocalyces

• Capsule

• Composed of organized repeating units of organic

chemicals

• Firmly attached to cell surface

• May prevent bacteria from being recognized by host

• Slime layer

• Loosely attached to cell surface

• Water soluble

• Sticky layer allows prokaryotes to attach to surfaces


Figure 3.5 Glycocalyces.

Glycocalyx

(capsule)

Glycocalyx

(slime layer)


External Structures of Bacterial Cells

• Flagella

• Are responsible for movement

• Have long structures that extend

beyond cell surface

• Are not present on all bacteria

• Structure

• Composed of filament, hook,

and basal body

• Basal body anchors the

filament and hook to cell wall


Figure 3.6 Proximal structure of bacterial flagella.

Filament

Direction

of rotation

during run

Peptidoglycan

layer (cell wall)

Cytoplasmic

membrane

Cytoplasm

Protein rings

Rod

Filament

Outer

membrane

Peptidoglycan

layer

Cytoplasmic

membrane Cytoplasm

Cell

wall

Outer

protein

rings

Rod

Integral

protein

Inner

protein

rings

Integral

protein

Basal

body

Gram – Gram +


Figure 3.8 Axial filament.

Axial filament

rotates around

cell

Outer

membrane

Cytoplasmic

membrane

Axial filament Spirochete

corkscrews

and moves

forward

Endoflagella

rotate

Axial filament

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Figure 3.10 Fimbriae.

Flagellum Fimbria

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Figure 3.11 Pili.

Pilus

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Bacterial Cell Walls

• Provide structure and shape and protect cell from

osmotic forces

• Assist some cells in attaching to other cells or in

resisting antimicrobial drugs

• Can target cell wall of bacteria with antibiotics

• Give bacterial cells characteristic shapes

• Composed of peptidoglycan

• Scientists describe two basic types of bacterial cell

walls:

• Gram-positive and Gram-negative

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Sugar

chain

Tetrapeptide

(amino acid)

crossbridge

Connecting chain

of amino acids

Figure 3.14 Possible structure of peptidoglycan.

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Bacterial Cell Walls

• Gram-Positive Bacterial Cell Walls

• Relatively thick layer of peptidoglycan

• Contain unique chemicals called teichoic acids

• Appear purple following Gram staining procedure

• Up to 60% mycolic acid in acid-fast bacteria helps cells

survive desiccation

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Prokaryotic Cell Walls

• Gram-Negative Bacterial Cell Walls

• Have only a thin layer of peptidoglycan

• Bilayer membrane outside the peptidoglycan contains

phospholipids, proteins, and lipopolysaccharide (LPS)

• Lipid A portion of LPS can cause fever, vasodilation,

inflammation, shock, and blood clotting

• May impede the treatment of disease

• Appear pink following Gram staining procedure

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Prokaryotic Cell Walls

• Bacteria Without Cell Walls

• A few bacteria lack cell walls

• Often mistaken for viruses due to small

size and lack of cell wall

• Have other features of prokaryotic cells

such as ribosomes

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Bacterial Cytoplasmic Membranes

• Structure

• Referred to as phospholipid bilayer

• Composed of lipids and associated proteins:

• Integral proteins

• Peripheral proteins

• Fluid mosaic model describes current understanding of

membrane structure

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Bacterial Cytoplasmic Membranes

• Functions?

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Cytoplasm of Bacteria

• Cytosol

• Liquid portion of cytoplasm

• Mostly water

• Contains cell's DNA in region called the nucleoid

• Inclusions

• May include reserve deposits of chemicals

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Figure 3.23 Granules of PHB in the bacterium Azotobacter chroococcum.

Polyhydroxybutyrate

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Cytoplasm of Bacteria

• Endospores

• Unique structures produced by some bacteria

• Defensive strategy against unfavorable conditions

• Vegetative cells transform into endospores when

multiple nutrients are limited

• Resistant to extreme conditions such as heat, radiation,

chemicals

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Figure 3.24 Formation of an endospore.

Steps in Endospore Formation

DNA is replicated.

Cytoplasmic membrane

invaginates to form

forespore.


grows and engulfs

forespore within a

second membrane.

Vegetative cell's DNA

disintegrates.

A cortex of pepti-

doglycan is deposited

between the membranes;

meanwhile, dipicolinic

acid and calcium ions

accumulate within the

center of the endospore.

Spore coat forms

around endospore.

Endospore matures:

Completion of spore coat.

Increase in resistance

to heat and chemicals by

unknown processes.

Endospore is released from

original cell.

Cell wall Cytoplasmic

membrane

DNA

Vegetative cell

Forespore

First

membrane

Second

membrane

Cortex

Spore coat

Outer

spore coat

Endospore

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Cytoplasm of Prokaryotes

• Nonmembranous Organelles

• Ribosomes

• Sites of protein synthesis

• Composed of polypeptides and ribosomal RNA

• Cytoskeleton

• Composed of three or four types of protein fibers

• Can play different roles in the cell:

• Cell division

• Cell shape

• Segregate DNA molecules

• Move through the environment

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External Structure of Eukaryotic Cells

• Glycocalyces

• Not 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

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Eukaryotic Cell Walls and Cytoplasmic

Membranes • Fungi, algae, plants, and some protozoa have cell

walls

• 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 a variety of

polysaccharides

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Eukaryotic Cell Walls and Cytoplasmic

Membranes • All eukaryotic cells have cytoplasmic membrane

• Are a fluid mosaic of phospholipids and proteins

• Contain steroid lipids to help maintain fluidity

• Contain regions of lipids and proteins called

membrane rafts

• Control movement into and out of cell

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Cytoplasm of Eukaryotes

• Flagella

• Structure and Arrangement

• Differ structurally and functionally from prokaryotic flagella

• Within the cytoplasmic membrane

• Shaft composed of tubulin arranged to

form microtubules

• Filaments anchored to cell by basal body;

no hook

• May be single or multiple; generally found

at one pole of cell

• Function

• Do not rotate but undulate rhythmically

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Figure 3.31c Eukaryotic flagella and cilia.


Cytosol

Central pair

microtubules

"9 + 2" arrangement Microtubules

(doublet)


Portion cut away to show transition area from doublets to triplets and the end of central microtubules

"9 + 0" arrangement

Microtubules

(triplet)

Basal body

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• Cilia

• Shorter and more numerous than flagella

• Coordinated beating propels cells through their

environment

• Also used to move substances past the surface of the

cell

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• Other Nonmembranous Organelles

• Ribosomes

• Larger than prokaryotic ribosomes (80S versus 70S)

• Composed of 60S and 40S subunits

• Cytoskeleton

• Extensive network of fibers and tubules

• Anchors organelles

• Produces basic shape of the cell

• Made up of tubulin microtubules, actin microfilaments,

and intermediate filaments

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Table 3.5 Nonmembranous and Membranous Organelles of Cells

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• 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

• Larger cell became dependent on parasites for aerobic

ATP production

• Aerobic prokaryotes evolved into mitochondria

• Similar scenario for origin of chloroplasts

• Theory is not universally accepted

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