SBU3043 CONCEPTS IN BIOLOGY Chapter 3 Cellular Basis of Life

SBU3043

CONCEPTS IN BIOLOGY

Chapter 3Cellular Basis of Life

SBU3043 Concepts in Biology

By Dr Somcit Sinang

Content

• 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

By Dr Somcit Sinang

What is a cell?

The cell theory states that cells are the fundamental units of life.

By Dr Somcit Sinang

The 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.

By Dr Somcit Sinang

How do we see cells?

Cell and scale

• 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.”

Cell size

• 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.

By Dr Somcit Sinang

Cell surface area-to-volume ratio

Biological sizes and cell diversity

By Dr Somcit Sinang

Modern microscopes: light

• 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.

By Dr Somcit Sinang

Modern microscopes: 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.

By Dr Somcit Sinang

Modern microscopes: Electron

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.

By Dr Somcit Sinang

Comparing light and electron microscopy

The Basics of Cell Structure

• Eukaryotic cell

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

• Prokaryotic cell

• Small, simple cells without a nucleus

By Dr Somcit Sinang

Introducing prokaryotic cells

By Dr Somcit Sinang

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).

By Dr Somcit Sinang

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

By Dr Somcit Sinang

Prokaryotic cells

By Dr Somcit Sinang

Prokaryotic cells

ARCHAE

General prokaryote body plan

• 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..

By Dr Somcit Sinang

General 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.

By Dr Somcit Sinang

Microbial mobs

Although prokaryotes are all single-celled, few live alone…

Microbial mobs

• 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.

By Dr Somcit Sinang

Microbial 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???

By Dr Somcit Sinang

Microbial 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.

Introducing eukaryotic cells

By Dr Somcit Sinang

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.

By Dr Somcit Sinang

Components of eukaryotic cells

By Dr Somcit Sinang

Plant cell

animal cell

Comparing between prokaryotic and eukaryotic cells

All Cells Have 3 Things In Common

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.

By Dr Somcit Sinang

Prokaryote

PlantAnimal

Membrane structure

By Dr Somcit Sinang

Cell membranes

• 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

By Dr Somcit Sinang

Membrane proteins

• 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

By Dr Somcit Sinang

Membrane proteins

Category Function Examples

Passive transporters Allow ions or small molecules to cross membrane to the lowconcentration 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 Histocompatibilitymolecules

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

The Nucleus

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

By Dr Somcit Sinang

The cellnucleus

By Dr Somcit Sinang

Components of the 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.

By Dr Somcit Sinang

• 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.

By Dr Somcit Sinang

• 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

By Dr Somcit Sinang

The Endomembrane system

The endomembrane 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

By Dr Somcit Sinang

Glycoprotein

Ribosomes

Rough ER

Golgi complex

Plasma

membrane

0.5µm

The components of endomembrane system

• 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.

By Dr Somcit Sinang

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.

By Dr Somcit Sinang

• II. Vesicles

• A variety of vesicles

• Peroxisomes

• Vesicles containing enzymes that break down hydrogen peroxide, alcohol, and other toxins.

• Vacuoles

• Vesicles for waste disposal

By Dr Somcit Sinang

• 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

By Dr Somcit Sinang

Golgi complex

Lysosomes

Mitochondriaplastids

central vacuole

By Dr Somcit Sinang

I. Mitochondria

• 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.

By Dr Somcit Sinang

Mitochondria

II. Plastids

• 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.

By Dr Somcit Sinang

Plastids• 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.

By Dr Somcit Sinang

Chloroplast

By Dr Somcit Sinang

Cellular respiration and photosynthesis

By Dr Somcit Sinang

III. The central vacuoles

• 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

Cell Surface Specializations

By Dr Somcit Sinang

Cell surface specialization

• 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.

By Dr Somcit Sinang

• 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 celluloseinto the coating around young plant cells

Secondary cell wall

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

By Dr Somcit Sinang

• II. Plant cuticle

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

By Dr Somcit Sinang

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

CELL SURFACE SPECIALIZATION

By Dr Somcit Sinang

Extracellular matrix

By Dr Somcit Sinang

• 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

CELL SURFACE SPECIALIZATION

By Dr Somcit Sinang

The dynamics of cytoskeleton

By Dr Somcit Sinang

• 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

CYTOSKELETON

By Dr Somcit Sinang

The Cytoskeleton

By Dr Somcit Sinang

• 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

COMPONENTS OF THE CYTOSKELETON

By Dr Somcit Sinang

• 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

COMPONENTS OF THE CYTOSKELETON

By Dr Somcit Sinang

Structure of cilia

SBU3043 CONCEPTS IN BIOLOGY Chapter 3 Cellular Basis of Life

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