Cellular Basis of Life: An Introduction

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HAPTER

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C ELLULAR B ASIS OF LIFE

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ONTENT

 The cell theory

 Modern microscopes

 Sizes and shapes

 Components of all cells

 Eukaryotic cells

 Cell structures and functions

 Plant and animal cell

 Higher levels of organization

 You will see how the properties of cell membranes emerge from the organization of lipids and

proteins.

 You will consider the cellular location of DNA and the sites where carbohydrates are built and

broken apart.

 You will also expand your understanding of the vital roles of proteins in cell functions and see how nucleotide helps control cells activities.

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HY LEARNING THIS CHAPTER IS IMPORTANT

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The hierarchy of biological organizations

W HAT IS A CELL ?

The cell theory states that cells are the

fundamental units of life.

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HE CELL THEORY EMERGES

 In 1839, Schleiden and Schwann proposed the basic concepts of the modern cell theory.

 All organisms consists of one or more cells.

 A cell is the smallest unit with the properties of life.

 Each new cell arises from division of another, pre-existing cell.

 Each cell passes its hereditary material to its offspring.

H OW DO WE SEE CELLS ?

 Cells are small and measured in micrometer (µm).

 They are invisible to the naked eye, so microscope help us to see

 The first microscopes were created in the 1600s.

 In 1800s, scientists view and describe sub cellular components.

 These observations formed the basis for the “cell theory.”

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ELL AND SCALE

 Surface-to-volume ratio restricts cell size by limiting transport of nutrients and wastes.

 A wide and thin cell, such as a nerve cell or a

microvillus has a greater surface area to volume ratio than a spheroidal cell.

 Increased surface area can also lead to biological problems.

 increases loss of water and dissolved substances.

 problems of temperature control.

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ELL SIZE

Cell surface area-to-volume ratio

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IOLOGICAL SIZES AND CELL DIVERSITY

 Many modern microscopes still rely on visible light to illuminate objects.

 Light microscope:

 Light pass through a cell or some other specimen.

 One or more curved glass lenses bend the light and focus it as a magnified image of the specimen.

 Only cells that are thin enough for light to pass through will be visible with a light microscope.

 Cells usually colorless, thus need to stain to enhance their image.

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ODERN MICROSCOPES

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LIGHT

 Types of light microscopes

 Phase-contrast microscopes

 Reflected light microscopes

 Fluorescence microscopes

A cell or the molecule is the light source; it

fluoresces or emits energy in the form of visible light, when a laser beam is focused on it.

Molecules such as chlorophyll fluoresce naturally.

More typically, researchers attach a light-

emitting tracer to the molecule/cell of interest.

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ODERN MICROSCOPES

:

LIGHT

 Use electrons to illuminate samples and reveal smaller details.

 Types of electron microscopes

 Transmission electron microscopes

Electrons form an image after they passed through a thin specimen.

The specimen’s internal details appear on the image as shadows.

 Scanning electron microscopes

Direct the beam of electrons back and forth across the surface of a specimen, which has been coated with a thin layer of gold or another metal.

The metal emits both electrons and x-rays, which will be converted into images.

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ODERN MICROSCOPES

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LECTRON

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OMPARING LIGHT AND ELECTRON MICROSCOPY

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HE

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ASICS OF

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ELL

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TRUCTURE

 Eukaryotic cell

 Cell interior is divided into functional compartments, including a nucleus

 Prokaryotic cell

 Small, simple cells without a nucleus

I NTRODUCING PROKARYOTIC CELLS

 Prokaryotes are single-celled organism that do not have a nucleus.

 Prokaryotes (“before the nucleus”), the smallest and most metabolically diverse forms of life.

 Prokaryotes are grouped into domains bacteria and archaea.

 Bacteria and archaea are similar in appearance and size, but differ in structure and metabolism.

 In many aspect, archaea resemble eukaryotic cells.

 In terms of size, prokaryotic cells are not much wider than a micrometer (µm).

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ROKARYOTIC CELLS

Phylogenetic tree showing the relationship between the archaea and other forms of life. Eukaryotes are colored red, archaea green and bacteria blue

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ROKARYOTIC CELLS

ARCHAE

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ROKARYOTIC CELLS

 Cell wall surrounds the plasma membrane

 A rigid, yet porous structure

 Made of peptidoglycan (in bacteria) or proteins (in archaea) and coated with a sticky capsule

 The capsule helps the cells to adhere to surfaces and protect from other pathogenic bacteria.

 Flagellum for motion

 Flagella move like a propeller that drives the cell through fluid habitat.

 Pili help cells move across surfaces

 Sex pilus aids in sexual

reproduction and transfer of

genetic materials…exp: disease causing bacteria..

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ENERAL PROKARYOTE BODY PLAN

 Plasma membrane, selectively control movement of substances to and from cytoplasm.

 A plasma membrane bristle with transporters, receptors and proteins that carry out important metabolic processes.

 Cytoplasm contains many ribosome on which polypeptide chains are assembled.

 Nucleiod is an irregular shaped region where DNA is located, but it is not enclosed.

 Prokaryotes have single chromosome that is circular DNA molecule.

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ENERAL PROKARYOTE BODY PLAN

M ICROBIAL MOBS

Although prokaryotes are all single-

celled, few live alone…

 Bacteria cells often live so close together that entire group shares a layer of secreted

polysaccharides and glycoproteins.

 Such communal life arrangement is called biofilm.

 Typically may include multiple species.

 May include bacteria, algae, fungi, protists, and archaeans.

 Such association allows cells to stay in a particular spot rather than be swept away by currents in a fluid habitat.

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ICROBIAL MOBS

 Wherever there is water, biofilms form.

 Slippery goo on river rocks, in water pipes, and in sewage treatment ponds.

 In human body? Contact lenses, lung, digestive tract…Where else???

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ICROBIAL MOBS

Bacteria and other microbes settle on a surface and reproduce. Slime holds them together in a biofilm. When condition become unfavorable, a biofilm’s inhabitants may revert to a flagellated

form and disperse.

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ICROBIAL MOBS

I NTRODUCING EUKARYOTIC CELLS

 Eukaryotic (“true nucleus”) cells carry out much of their metabolism inside membrane-enclosed

organelles

 Organelle

 A structure that carries out a specialized function within a cell

 Bounded by membranes to control the types and amounts of substances that cross over organelle.

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UKARYOTIC CELLS

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OMPONENTS OF EUKARYOTIC CELLS

Plant cell

animal cell

C OMPARING BETWEEN

PROKARYOTIC AND EUKARYOTIC

CELLS

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LL

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ELLS

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AVE

3 T

HINGS

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OMMON

 Plasma membrane

 Controls substances passing in and out of the cell

 Water, CO₂, O₂ and other substances

 DNA containing region

 Nucleus in eukaryotic cells

 Nucleoid region in prokaryotic cells

 Cytoplasm

 A semifluid mixture containing cell components.

 Holds many ribosomes, structures on which protein are built.

Prokaryote

Plant Animal

1. M EMBRANE STRUCTURE

 Lipid bilayer

 A double layer of phospholipids organized with their hydrophilic heads outwards and their hydrophobic tails inwards

 Many types of proteins embedded or attached to the bilayers carry out membrane functions

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REVIEW OF CELL MEMBRANES

 Proteins carry out nearly all membrane tasks.

 Many span the lipid bilayers and often project beyond it.

 Main categories of membrane proteins:

 Transporters

 Receptors

 Recognition proteins

 Adhesion proteins

 Communication proteins

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EMBRANE PROTEINS

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EMBRANE PROTEINS

Category Function Examples

Passive

transporters Allow ions or small molecules to cross membrane to the low

concentration gradient

Porins; Glucose transporter

Active

transporters Pump ions or molecules to the side with higher concentration gradient; require ATP

Calcium pump;

serotonin transporter Receptors Initiate change in cell activity

by responding to outside signal Insulin receptor Cell adhesion

molecules (CAMs) Help cells stick to one another

and protein matrix Integrins Recognition

proteins

Identify cells as self or non-self Histocompatibility molecules

Communication

proteins Join together and form cytoplasm-to-cytoplasm junctions to allow ions and small molecules pass freely between adjacent cells

Connexins in gap junction

2. T HE N UCLEUS

The nucleus keeps eukaryotic DNA away from potentially damaging reactions in the

cytoplasm.

The cell

nucleus

 Nuclear envelope

 Two lipid bilayers pressed together as a single membrane surrounding the nucleus

 Outer layer is continuous with the Endoplasmic Reticulum (ER)

 Receptors, pores, and transporters on the nuclear envelope control when and how much information encoded in DNA gets used.

 Nuclear pores allow certain substances to pass through the membrane.

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OMPONENTS OF THE NUCLEUS

 Nucleoplasm

 Viscous fluid inside the nuclear envelope, similar to cytoplasm

 Nucleolus

 A dense region in the nucleus where subunits of ribosomes are assembled from proteins and RNA.

 Rounded mass of proteins and copies of genes for ribosomal DNA used to construct ribosomal

subunits.

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OMPONENTS OF THE NUCLEUS

 Chromatin

 Total collection of all DNA molecules and associated proteins in the nucleus; all of the chromosomes.

 Chromosome

 A single DNA molecule with its attached proteins.

 During cell division, chromosomes condense and become visible in micrographs

 The genetic material inside eukaryotic cells is distributed among a number of chromosomes that differ in length and shape.

 Human body cells have 46 chromosomes

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OMPONENTS OF THE NUCLEUS

3. T HE E NDOMEMBRANE SYSTEM

 Endomembrane system is a set of interacting organelles between the nucleus and the plasma membrane.

 It include Endoplasmic Reticulum (ER), Golgi bodies, vesicles.

 Makes lipids, enzymes, and proteins for secretion or insertion into cell membranes

 Other specialized cell functions

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HE ENDOMEMBRANE SYSTEM

Glycoprotein

Ribosomes Rough ER

cis face

trans face

Golgi complex Plasma

membrane

0.5µm

 I. Endoplasmic reticulum (ER)

 An extension of the nuclear envelope that forms a continuous, folded compartment

 Two kinds of endoplasmic reticulum

 Rough ER (with ribosomes) folds polypeptides into their tertiary form.

 Smooth ER (no ribosomes) makes lipids, breaks down carbohydrates and lipids, detoxifies poisons.

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HE COMPONENTS OF ENDOMEMBRANE SYSTEM

Endoplasmic reticulum (ER)

 II. Vesicles

 Small, membrane-enclosed saclike organelles that store or transport substances

 Endomembrane system include diverse vesicles.

Endocytic type form as a patch of plasma membrane sinks into the cytoplasm.

Exocytic type buds from ER or golgi

membranes and transport substances to the plasma membrane for export.

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HE COMPONENTS OF ENDOMEMBRANE SYSTEM

 II. Vesicles

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HE COMPONENTS OF ENDOMEMBRANE SYSTEM

 A variety of vesicles

 Peroxisomes

Vesicles containing enzymes that break

down hydrogen peroxide, alcohol, and other toxins.

 Vacuoles

Vesicles for waste disposal

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HE COMPONENTS OF ENDOMEMBRANE SYSTEM

 III. Golgi body

 A folded membrane containing enzymes that finish polypeptides and lipids delivered by the ER

 Packages finished products in vesicles that carry them to the plasma membrane or to lysosomes

 IV. Lysosomes

 Buds from golgi bodies

 Contain enzymes and take part in intracellular digestion.

 When lysosomes do not work properly, some cellular materials are not properly recycled

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HE COMPONENTS OF ENDOMEMBRANE SYSTEM

Golgi complex

Lysosomes

4. O THER ORGANELLES : M ITOCHONDRIA

PLASTIDS

CENTRAL VACUOLE

 Mitochondria specializes in aerobic respiration, an oxygen-requiring metabolic pathways that

produces many ATP by breaking down organic molecules.

 A cell in liver, heart and skeletal muscles and other tissues that demand high energy may contain >1000 mitochondria.

 A mitochondrion has two membranes; one is folded inside the other.

 Hydrogen ions accumulate between the two

membranes, flow across the inner membrane to the interior of ATP synthetase.

 That flow drives the formation of ATP.

I. M

ITOCHONDRIA

Mitochondria

 Many plant cells have plastids, which are organelles of photosynthesis, storage or both.

 Plastids may include chromoplasts, amyloplasts (??), and chloroplasts

 Only photosynthetic eukaryotes cells contain plastids called chloroplast.

II. P

LASTIDS

 Chloroplasts

 Tiny sugar factory which trap sunlight energy and drives photosynthesis.

 ATP and NADPH form, and then both are used to produce glucose from CO₂.

 Two outer membranes enclose its semi-fluid interior called stroma.

 Stroma is a place where glucose and other organic molecules are assembled.

 The third membrane is called thylakoid membrane is folded up inside the stroma and form a continuous compartment.

 During photosynthesis, chlorophyll are

embedded inside the thylakoid membrane to trap light energy.

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LASTIDS

Chloroplast

Cellular respiration and photosynthesis

 Central vacuole

 A plant organelle that occupies 50 to 90 percent of a cell’s interior

 Stores amino acids, sugars, ions, wastes, toxins

 Fluid pressure keeps plant cells firm

III. T

HE CENTRAL VACUOLES

5. C ELL S URFACE S PECIALIZATIONS

 For many eukaryotic cells, a porous wall or

protective covering intervenes between the plasma membrane and the surrounding.

 In animal tissues, one plasma membrane may press right up to another, and matrices and junctions

usually form between them.

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ELL SURFACE SPECIALIZATION

 I. Eukaryotic Cell Walls

 Cell walls → in plant cells and many protist and fungal (Animal cell → NO CELL WALL)

 Primary cell wall

 A thin, pliable wall formed by secretion of

cellulose into the coating around young plant cells

 Secondary cell wall

 A strong wall composed of lignin, formed in some plant stems and roots after maturity

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ELL SURFACE SPECIALIZATION

 II. Plant cuticle

 A waxy covering that protects exposed surfaces and limits water loss

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ELL SURFACE SPECIALIZATION

 III. Matrixes between animal cells

 Most cells of multi-celled organisms are surrounded by extracellular matrix.

 Extracellular matrix (ECM)

 Complex mixture of fibrous proteins and polysaccharides secreted by surrounding cells.

 It supports and anchors cells, separate tissues, and function in cell signaling.

 Primary cell walls are a type of extracellular matrix, which in plant is mostly cellulose.

 In fungi, ECM is mainly chitin.

 Bone is mostly ECM, composed of collagen (fibrous protein) and mineral deposits

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ELL SURFACE SPECIALIZATION

Extracellular matrix

 IV. Cell junctions

 Allow cells to interact with each other and the environment.

 Cells can send or receive signals or materials through some types of junctions.

 Other types of junctions helps cells recognize and stick to each other or to extracellular

matrix.

 In plants, plasmodesmata extend through cell walls to connect the cytoplasm of two cells

 Animals have three types of cell junctions:

tight junctions, adhering junctions, gap junctions

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ELL SURFACE SPECIALIZATION

6. T HE DYNAMICS OF CYTOSKELETON

 Cytoskeleton is an extensive and dynamic internal framework in eukaryotic cell.

 An interconnected system of many protein filaments

 Parts of the cytoskeleton reinforce, organize, and move cell structures or a whole cell

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YTOSKELETON

The Cytoskeleton

 I. Microtubules

 Long, hollow cylinders made of tubulin

 Form dynamic scaffolding for cell processes

 II. Microfilaments

 Consist mainly of the globular protein actin

 Make up the cell cortex

 III. Intermediate filaments

 Maintain cell and tissue structures

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OMPONENTS OF THE CYTOSKELETON

 IV. Motor proteins

 Accessory proteins that move molecules through cells on tracks of microtubules and microfilaments

 Energized by ATP

 Example: kinesins

 Eukaryotic flagella and cilia

Whiplike structures formed from microtubules organized into 9 + 2 arrays

Grow from a centriole which remains in the cytoplasm as a basal body

 Psueudopods

“False feet” used by amoebas and other eukaryotic cells to move or engulf prey

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OMPONENTS OF THE CYTOSKELETON

Structure of cilia

 There is an antibiotic for treatment of infection. The antibiotic acts by combining with the bacteria’s

causing them to lose their function by inhibit the protein synthesis.

 When a potted house plant is wilting, the addition of water quickly changes the look of the plant. Why?

 Which organelle would be abundant in a sperm cell that is seeking to fertilize an egg cell?

 A tadpole that is undergoing metamophosis into a frog and losing the need for a tail would see abundant numbers of what organelle to help assist in the tail loss?

 Disease-causing bacteria often attach to cells they attack. What are the bacterial structures used to aid that attachment?

 One of the functions of cytoskeleton in animal cells is to give shape to the cell. Plant cells have a fairly rigid cell wall surounding the plasma membrane. Does this mean that a cytoskeleton is unnecessary for a plant cell?

Please visit this website:

http://www.wadsworthmedia.com/biology/0495119814_st arr/big_picture/ch04_bp.html

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UMMARY