1.1 cell structure
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What are characteristics of living things?
Organisation
Response to stimuli
Homeostasis (maintaining stable
internal conditions),
Change through the time…
Metabolism
Growth and development
Reproduction
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
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
Two Types of Cells
Prokaryotic cells (without membrane-bound structures)
Eukaryotic cells (with membrane-bound structures)
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 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
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
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
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
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
• 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
• 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
• 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
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
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
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
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
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
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