What are characteristics of living things?

Organisation

Response to stimuli

Homeostasis (maintaining stable

internal conditions),

Change through the time…

Metabolism

Growth and development

Reproduction

CELL STRUCTURE AND CELL STRUCTURE AND

FUNCTIONSFUNCTIONS

All living things are made of organized

parts, obtain energy from their

surroundings, perform chemical reactions,

respond to their environment, grow and

develop, change with time, and reproduce

A cell is the smallest unit that can

carry on all of the processes of life

Cell TheoryCell Theory • The cell theory grew out of the work of many scientists and improvements in the microscope.

• The cell theory is a unifying concept of biology.

• In 1665, Robert Hooke discovered cells in slices of cork. • In 1673, Anton van Leeuwenhoek was the first to observe living cells in microorganisms; Leeuwenhoek called these organism animalcules (now called protists).

Cell Theory • All organisms are made of cells

• All cells are produced from other cells (all cells arise from pre-existing cells by cell division)

• The cell is the most basic unit of life

What is a cell? How do cells organise in

living things?

Cell Diversity

Amoeba Proteus

Nerve Cell

Bacteria

Plant Stem

Red Blood Cell

All cells share certain characteristics

• Cells tend to be microscopic

• All cells are enclosed by a membrane

• All cells are filled with cytoplasm

• Unicellular organisms are made up of one cell

• Multicellular organisms are made up of many cells that often specialize according to function - differentiation

cell membrane

cytoplasm

Cell Size – Cell size is limited by a cell’s surface

area–to-volume ratio.

Cell size differs amongst species

Cell Shape – A cell’s shape reflects its function

Two Types of Cells

Prokaryotic cells (without membrane-bound structures)

Eukaryotic cells (with membrane-bound structures)

Prokaryotic cell (‘pro’ - before, ‘karyon’ – nucleus)

Prokarotic cells

• Do not have a nucleus and membrane-bound organelles

• Have few internal structures

• Single, circular chromosome in nucleoid region

• Surrounded by cell membrane and a cell wall made up of peptidoglycan

• Prokaryotic cells are one-celled

organisms: bacteria

• Divided into two domains,

i.e., Archaea and Bacteria

Eukaryotic cell (‘eu’ - proper, ‘karyon’ – nucleus)

Eukaryotic cells

• Cells have a nucleus and membrane-bound organelles

• Incudes protists, fungi, plants, and animals

• The three basic parts of a cell are the plasma membrane, the cytoplasm, and the nucleus.

Prokaryotic cell Eukaryotic cell

Organisms bacteria protists, fungi, plants,

animals

Size ~ 1-10 µm ~ 10-100 µm

Structure

• Most have a cell wall and some have a capsule surrounding it

• Lack nucleus and many organelles

• Ribosomes 70S (50S + 30S)

• Only plant cells have cell wall

• Has typical nucleus and many organelles

• Ribosomes 80S (60S + 40S)

Prokaryotic cell vs. Eukaryotic cell

Virus

• No nucleus

• No membranes

• No organelles

• Cannot reproduce on its own

• Generally not considered alive by most standards

Flu virus

T4 Bacteriophage

HIV

A cell A cell is a basic unit of life, that is capable of

performing life functions

A cell can be likened to a factory

Each part of the

cell has their own

structure and

function

Cell membrane

Endoplasmic

reticulum (ER)

Nucleus

Ribosome Lysosome

Mitochondrion

Golgi body

Animal Cell

Plant Cell

Surrounding the Cell

Cell Membrane

Cover the cell’s surface

Act as a barrier between inside and outside of the cell

Controls the transport of materials in and out of the cell

cell membrane outside cell

inside cell

Cell Membrane

• Double layer of phospholipids that is highly fluid without breaking.

• Embedded proteins in the lipid layer and give the membrane its mosaic character - fluid mosaic.

• Selectively permeable

protein

cholesterol

protein carbohydrate

chain

protein channel

Phospholipid bilayer

• The fluid portion of the membrane

• Phospholipid molecules have:

* A polar head group, hydrophilic and points toward the aqueous environment on both sides of the membranes

* A pair of nonpolar tails, hydrophobic and point away from the aqueous environments and toward each other

Membrane structure

Phospholipid bilayer

• Establish the physical integrity of the membrane

• Create an effective barrier to the rapid passage of hydrophilic materials such as water and ions

• Serves as a lipid “lake” in which a variety of proteins “float”

Membranes also contain cholesterol, which is important to membrane integrity and fluidity. Cholesterol prevents the phospholipid from packing tightly together, thus make the cell surface more flexible and stable and prevents freezing in low temperatures

Membrane Proteins

– Cell membranes often contain proteins embedded within the phospholipid bilayer.

– Proteins help move large molecules or aid in cell recognition (peripheral and integral)

Cell Wall

• Most commonly found in plant cells & bacteria

• Outermost layer of a plant cell (made of cellulose)

• Permeable, contains small pores to move water and oxygen and carbon dioxide in and out.

• Maintains structure, supports & protects the cell

Inside the Cell

Protoplasm: a clear substance like jelly which forms the living part of an animal or plant cell including the nucleus

Protoplasm: cytoplasm + nucleus

Cytoplasm: cytosol + many organelles

Cytoplasm: all the living material in a cell, not including the nucleus

Organelle: a membrane-bound structure within a cell which carries out a particular function

Nucleus

• Separate from cytoplasm by double membrane

• Contains genetic material - DNA

• Controls all the activities of the cell

Nuclear Membrane (nuclear envelope)

• Surrounds nucleus

• Made of two layers

• Pores allowing material to enter and leave nucleus

Chromosomes Made of DNA and proteins

Contain instructions for traits & characteristics

Chromatin condenses to form discrete chromosomes as a cell prepares to divide.

Nucleolus The site of ribosomal RNA synthesis

Cytoplasm

• Jelly-like substance

• Contains organelles, cytoskeleton, fluid including molecules (proteins, water, food and wastes)

• Medium for chemical reaction – Cytosol includes molecules and small particles, such as

ribosomes, but not membrane bound organelles. About 20% of the cytosol is made up of protein

Cytoskeleton

• Maintains cell shape and support

• Helps position and transport organelles

• Provides strength

• Assists in cell division

• Aids in cell movement

Cytoskeleton

Cytoskeleton

• Consists of microtubules, microfilaments and intermediate filaments

• The microtubules assist in cell division by moving the cells apart.

• Microfilaments are made of protein and help with muscle contractions.

• Both help support the cell and give structure but do allow for movement.

Cilia and Flagella

• Hairlike structures that extend from the surface of the cell, where they assist in movement

• Some cells have flagella. (usually only one)

• Many cells have cilia (thousands)

• A flagella is like a whip.

• Cilia are like tiny paddles.

• Cilia and flagella are made of microtubules.

Cilia

Flagella

Endoplasmic Reticulum

Endoplasmic Reticulum

• Continuous with the nuclear membrane

• Involved in cell product transport of proteins and lipids

• The rough and smooth ER are sometimes attach to each other.

• Rough ER: surface covered with ribosomes and prepares proteins for export or insertion into the cell membrane.

– Most abundant in cells that produce large amounts of protein for export, such as digestive glands and antibody-producing cells

Endoplasmic Reticulum

• Smooth ER: lacks ribosomes and makes lipids such as steroids participates in detoxification of toxins.

– In ovaries and testes, smooth ER produces estrogen and testosterone, respectively

– In skeletal and heart muscle cells, smooth ER releases calcium, which stimulates contraction

– Abundant in liver and kidneys for detoxification

Ribosomes

Nucleus

Ribosomes

• Each cell contains thousands

• Float freely in cytoplasm or attached to rough endoplasmic reticulum

• Made of protein and rRNA. Ribosome assembly begins in the nucleolus and is completed in the cytoplasm

• Site of protein synthesis

Ribosomes

Golgi Body

• A system of membranes that work closely with the ER

• Consists of flattened membranous sacs called cisternae

• Involves in processing, packaging and secreting of proteins/lipids

cis face

(“receiving” side of

Golgi apparatus)

trans face

(“shipping” side of

Golgi apparatus)

0.1 m

TEM of Golgi apparatus

Cisternae

The Golgi apparatus

Vesicle

Vesicles are membrane-bound sacs that hold materials

Lysosome

• Surrounded by single membrane

• Contains hydrolytic enzyme

• Digestive 'plant' for proteins, fats, carbohydrates and nucleic acid as well as old organelles, viruses and bacteria.

• Transports undigested material to cell membrane for removal

• Cell breaks down if lysosome explodes

Lysosomes are rare in plant cells

Peroxisome

• Small organelles with a single membrane and a granular interior containing specialized enzymes

• Collect the toxic peroxides (eg. H2O2) that are the unavoidable by-products of chemical reactions and break them down without mixing with other parts of the cell.

Glyoxysome, a structurally similar organelle found only in plants especially in young plants, are the sites where stored lipids are converted into carbohydrates for transport to growing cells

Mitochondrion

• Rod-shaped organelle with double membrane

• Produces energy (ATP) through chemical reactions

• Have their own DNA which only comes from the mother.

Vacuoles

• Large and permanent in plants

• Contains sap fluid

• Storage areas for cellular products and substances such as water, waste, enzymes and poisons

• Help plant cells maintain shape

Plastid

• Plastids store starch and pigments.

– Chloroplasts – contain green pigment, chlorophyll that absorbs light energy to make carbohydrates

– Chromoplasts – contain colorful pigments

– Amyloplasts – store starch

Chloroplast

• Found only in plant cells and some protists

• Have double membrane and their own DNA

• Contains chlorophyll

• Carry out photosynthesis in the presence of sunlight, water and carbon dioxide

Centrioles

• Only in animal cell

• Found near nucleus

• Tubes found in the centrosomes

• Consist of two short cylinders of microtubules at right angles to each other

• Involved in cell division

• Centrioles form cilia and flagella

Are plant cells like animal cells? With the

same structure?

A typical plant cell has a more regular and rigid

shape as compared to a typical animal cell.

They contain other organelles that are not found in

animal cells such as cell wall, chloroplasts

Animal Cell and Plant Cell

Plant Cells Vs. Animal Cells

• Contain chloroplasts for photosynthesis

• Have a cell wall to maintain structure and rigidity

• Centrioles are absent

• Usually do not contain lysosomes

• Have one large central vacuole

• Cells are square and rigid or geometric shaped

• No chloroplasts

• No cell wall

• Centrioles are present

• Contain lysosomes

• Has small and few vacuoles

• Cells are fluid and flexible, many shapes

1. Which organelle synthesizes proteins?

A. Nucleus B. Ribosome

C. Centriole D. All above

2. Most of a cell's ATP is synthesized by membrane-bound

organelles called

A.Vacuole B. Ribosome

C. Mitochondria D. Nucleus

3. Which organelle modifies, packages, and sorts proteins

for secretion or use within the cell?

A. Mitochondria B. Golgi body

C. Nucleus D. Endoplasmic

reticulum

In Humans

In Plants

Cell

↓

Tissue

↓

Organ

↓

System

↓

Organism

How big is a cell?

Kính hiển vi quang học

Kính hiển vi điện tử

Tế bào trứng cá

Đa số

tế bào thực vật

và

động vật

Lục lạp

Đa số vi khuẩn

Phage T2

Lipits

Proteins

Nguyển tử

Các phân tử nhỏ

Cell size

The Microscope in Cell Studies

• 2 different types of microscopes:

i) light microscope – uses light as a source of radiation

ii) electron microscope – uses electrons

UNSWFYBIO/2008JK

Magnification and Resolution

• Magnification

- the number of times larger an image is compared with the real size of the object

- magnification = size of image

actual size of specimen

• Resolution

- the ability to distinguish between two separate points

UNSWFYBIO/2008JK

Light microscope

Electron microscope

Electron microscope

Comparison of advantages and disadvantages of the light and electron microscope

LIGHT MICROSCOPE ELECTRON MICROSCOPE

Advantages Disadvantages

Cheap to purchase Expensive to purchase

Cheap to operate – uses a little electricity where there is a built-in light source

Expensive to operate – requires up to 100 000 volts to produce the electric beam

Small and portable Very large and must be operated in special rooms

Unaffected by magnetic fields Affected by magnetic fields

Preparation of material is relatively quick and simple, requiring only a little expertise

Preparation of material is lengthy and requires considerable expertise and sometimes complex equipment

Material rarely distorted by preparation Preparation of material may distort it

Living as well as dead material may be viewed A high vacuum is required and living material cannot be observed

Natural colour of material can be observed All images are in black and white

Disadvantages Advantages

Magnifies objects up to 1500X Magnifies objects over 500 000X

Can resolve objects up to 200 nm apart Has a resolving power for biological specimens of around 1 nm

The depth of field is restricted It is possible to investigate a greater depth of field