Cell Structure And Functions.pdf 1w5n56

2.0 CELL STRUCTURE AND FUNCTIONS 9 HOURS Retold by, Amran Md Said

2.0 CELL STRUCTURE AND FUNCTIONS

2.1

2.3

Prokaryotic and eukaryotic cells Structures and functions: cell membrane and organelles

2.2

Microscopic structures of plant and animal cells

2.4

Cells transport

2.5

Cells are grouped into tissues

1st Hour Lecture Learning Outcomes : 2.1 Prokaryotic and eukaryotic cells : a.

state the cell theory

b.

Describe and compare the structures of prokaryotic and eukaryortic cells

2.2 Microscopic structures of plant and animal cells : a. Illustrate the detailed structures of typical plant and animal cells. b. Compare plant and animal cells

Introduction 1665 – Robert Hooke using an improved compound microscope, examine cork and used the term ‘cell’ to describe its basic units

Observation by Robert Hooke

Cork tissue Cork microscope

Cell Theory •1838 & 1839  Matthias Schleiden (a botanist) and Theodor Schwann (a zoologist) proposed the cell theory • Stating that the basic unit structure and function in living organism is the cell

Other important discovery 1855 – Rudolf Virchow postulate that all cells arise from pre-existing cells by cell division

Cell as the smallest independent unit of life and form the basis of living organism All living organism are made of one or more cells A cell is always surrounded by a cell surface membrane Contains a solution of protein and other substances in water. This solution is called cytoplasm Within the cytoplasm there are many structure called organelles

Four ideas of cell theory 1. The cell is the basic units of structure in living things 2. The cell is derived from other cell by cell division 3. The cell contains heredity material 4. The cell is the functioning unit of life

Prokaryotic and eukaryotic cells Prokaryotic Means ‘before nucleus’ Cells without nucleus Unicellular All bacteria and cyanobacteria

Eukaryotic Means ‘true nucleus’ Cells with nucleus Unicellular and multicellular E g. plants, algae, fungi and animals

Cell size

Prokaryotic cell

a) Bacteria

b) Cyanobacteria

What is Prokaryotic cell? Definition : A prokaryotic cell is a type of cell without a membrane-bound nucleus and other membrane-bound organelles An organism composed of a prokaryotic cell is called a prokaryote

Structure of Prokaryotic cell e g. bacteria

Capsule mesosome

Structure of bacteria Structures always present 1) Cell wall

Rigid; strengthening material is peptidoglycan

2) Plasma membrane

A partially permeable, contain proteins and phospholipids

3) Cytoplasm An aqueous substance, contain ribosome, DNA and stored granules of various substances

Structure of bacteria Structures always present 4) DNA

Circular molecule, not associated with protein, forming an area called the nucleoid

5) Ribosome 70S ribosomes, smaller than 80S eukaryote ribosomes, site of protein synthesis

Structure of bacteria Structures sometimes present 1) Flagellum

For locomotion, very simple structure ( not in 9+2 ), one or more may be present

2) Pili

One to several hundred for attachment to other cells or surfaces, involved in ‘sexual reproduction’

pili

Structures sometimes present 3) Mesosome

Infolding of the cell surface membrane, there are enzymes engaged in the synthesis of ATP molecules

4) Capsule

For additional protection

5) Plasmid

Small circle of DNA

plasmid

Eukaryotic cell

What is Eukaryotic cell? Definition : A type of cell that has a membrane-bound nucleus, membrane-bound organelles and DNA is associated with histone protein An organism composed of a eukaryotic cell is called eukaryote.

Structure of eukaryotic cell 1) Plasma membrane

A partially permeable, contains proteins and phospholipids

2) Cell wall

Rigid; strengthening material is cellulose (in plant) and chitin (in fungi)

3) Cytoplasm An aqueous substance, contains a variety of organelles and stored granules of various substances

Cont. Structure of eukaryotic 4) DNA

Inside the nucleus ,linear strand molecule and combined with histone protein

5) Cilia and For locomotion, flagella complex structure with 9+2 arrangement of microtubules

DNA wound around a cluster of histone molecules

Linker DNA

Nucleosome (11nm diameter)

Flagellum

Cilia

The differences between prokaryotes and eukaryotes Prokaryote

Eukaryote

Cell size is small (diameter 0.5-10 μm) Cell division is not by mitosis, mostly binary fission DNA is circular, freely in cytoplasm, ‘naked’ DNA without histone protein

Cell size is bigger (diameter 10-100 μm) Cell division is by mitosis, meiosis or both DNA is linear and contain in nucleus DNA is associates with histone protein

Prokaryote

Eukaryote

Organelles present are few , none with envelope

Organelles present are many , with envelope except ribosome

Cell wall is Cell wall is composed of composed of murein cellulose in plant cell walls or peptidoglycan and chitin in fungal walls

Prokaryote

Eukaryote

Type of flagella is fine, Type of flagella is simple and only consists complex, with 9+2 of one microtubule arrangement of microtubules Respiration is occurs in mesosomes of bacteria or cytoplasmic membranes of cyanobacteria

Respiration is occurs in mitochondria

Prokaryote

Eukaryote

Photosynthesis is occur not in chloroplasts, but takes place on membranes which show no stacking

Photosynthesis is occur in chloroplast containing membranes which are usually stack into lamellae or grana

Few prokaryote can fix nitrogen

No eukaryote can fix nitrogen

Prokaryote

Eukaryote

Centrioles absent

Centrioles present in animal cells

Ribosomes 70s

Ribosomes 80s

Capsule present in some prokaryotic cells

Capsule absent

Example Prokaryotes • Bacteria and cyanobacteria Eukaryotes • Algae, fungi, protozoa, plants and animals

2.2 Microscopic structure of plant and animal cells Learning Outcomes :

a) Illustrate the detailed structure of typical plant and animal cells b) Compare plant and animal cells

Microscopes Light microscope

Electron microscope

Plant cell under light microscope

E g. Onion cell

Animal cell under light microscope

E g . Cheek cells

Plant cell under electron microscope

Animal cell under electron microscope

STRUCTURE OF TYPICAL PLANT CELL

Structure of typical plant cell 1) Cell wall

Composed of cellulose, provides structural , fully permeable

2) Cell membrane

Surrounds the cytoplasm, controls the entry and exit of dissolved substance

Structure of typical plant cell 3) Cytoplasm

 Cytoplasm pressed firmly against the cell wall by a large fluid-filled vacuole  Contain water, dissolved substance such as amino acid and sugars, the various organelles

Structure of typical plant cell 4) Vacuole

 Large, contain sap cell, water necessary to provide turgor pressure  Bounded by a specialized membrane called ‘tonoplast’

5) Nucleus

Contains the genetic material and controlling the activities

Structure of typical plant cell 6) Chloroplast

Contain the pigment chlorophyll and enzyme for photosynthesis

7) Starch granules

Storage form of carbohydrate

Structure of typical plant cell 8) Plasmodesmata Cytoplasmic connections between cells

STRUCTURE OF TYPICAL ANIMAL CELL

STRUCTURE OF TYPICAL ANIMAL CELL 1) Cell membrane

Surrounds the cytoplasm, responsible for separating the cell contents from its surroundings

2) Cytoplasm

Often denser, with many more organelles and dissolved substances

STRUCTURE OF TYPICAL ANIMAL CELL 3) Vesicle

Small , can be involved with digestion (e.g. in phagocytosis) or with excretion

4) Nucleus

Controlling the activities and characteristics of the cell

5) Glycogen Storage form of granules carbohydrates

Difference between plant and animal cells Animal Cells

Plant Cells

• Have only cell surface membrane

• The cell surface membrane is surrounded by rigid cellulose cell wall

• No plasmodesmata and pits

• Plasmodesmata and pits present in cell wall

• No chloroplast

• Chloroplast present in photosynthetic cells

• Have small, temporary vesicles

• Large, permanent central vacuole filled with cell sap

• No tonoplast

• Tonoplast envelopes the vacuole

Difference between plant and animal cells Animal Cells

Plant Cells

• Centrioles present

• No centrioles

• Contain glycogen granules

• Contain starch granules

• Some cells are flagellated or ciliated

• Flagellated cells are found only in lower level plants (male gamete cells) • No lysosome

• Lysosomes present

2.3 Stucture and functions : cell membrane and organelles

2nd and 3rd Hour Lecture Learning Outcomes : 2.3 Stucture and funtions : cell membrane and organelles a.

Describe the structure of the plasma membrane and the functions of each of its components.

b.

Describe the functions of the plasma membrane

c.

Describe the structure and functions of the following organelles: •

Nucleus, mitocondria, rough and smooth endoplasmic reticulum, golgi body, ribosome, lysosome,chloroplast, centriole

Structure & function

Organelles

Not organelles Nucleus

Cell wall (plant)

Cell membrane

ER- smooth, rough

Cytoplasm Golgi body Mitochondrion Vacuole

Lysosome

Centriole

Ribosome

Cytoskeleton

Chloroplast

Membrance Plasma

Structure of the plasma membrane

MEMBRANE STRUCTURE The plasma membrane separates the living cell from its nonliving surroundings. This membrane : Is about 8 nm thick Surround the cell and controls traffic into and out of the cell Is selectively permeable, allowing some substances to cross more easily than others.

The phospholipids and proteins in membranes create a unique physical environment, described by the fluid mosaic model. A MEMBRANE is a fluid structure with proteins embedded or attached to a double layer of phospholipids.

Singer and Nicolson Fluid Mosaic Model • 1972 – S.Jonathan Singer and Garth Nicolson proposed the Fluid Mosaic Model • The model envisions a membrance as a mosaic of protein discontinuously embedded in, or at least attached to, a fluid phospholipids bilayer

PHOSPHOLIPIDS Phospholipids and most other membrane constituents are amphipathic molecules. Amphipathic molecules have both hydrophobic regions and hydrophilic regions.

Hydrophobic tails

Hydrophilic heads

Protein • Envision the membrance as a mosaic of protein floating in and fluid phospholipids bilayer. • They have 2 type of protein a) integral protein b) peripheral protein

Continue.. Protein are individually embedded in the phospholipid bilayer, rather than forming a solid coat spread upon the surface. Integral proteins (Intrinsic proteins), straight through the membrane and have both an intracellular and extracellular portion. Peripheral proteins (Extrinsic proteins), are fixed in one half of the bilayer or appendages loosely bound to the surface of membrane.

MEMBRANE STRUCTURE

Continue..

Hydrophilic portion of both proteins and phospholipids are maximally exposed to water resulting in a stable membrane structure. Hydrophobic portion of proteins and phospholipids are in nonaqueous environment inside the bilayer.

The functions of proteins on plasma membrane 1.Transport 2.Enzymatic activity 3.Signal transduction 4.Cell-cell recognition 5.Intercellular ing 6.Attachment to the cytoskeleton and extracellular matrix (ECM)

1. TRANSPORT • (a) A protein that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute.

1. TRANSPORT (cont..) • (b) Some transport proteins hydrolyze ATP as an energy source to actively pump substances across the membrane.

2. ENZYMATIC ACTIVITY • A protein built into the membrane may be an enzyme with its active site exposed to substances in the adjacent solution.

2. ENZYMATIC ACTIVITY (cont..) • In some cases, several enzymes in a membrane are ordered as a team that carries out sequential steps in a metabolic pathway.

3. SIGNAL TRANSDUCTION • A membrane protein may have a binding site with a specific shape of a chemical messenger. E.g. Hormone

Hormone or external message

3. SIGNAL TRANSDUCTION (cont..)

• The external messenger (signal) may cause a conformational change in the protein that relays the message to the inside of the cell.

Hormone or external message

4. INTERCELLULAR ING •Membrane proteins of adjacent cell may be hooked together in various kind of junction.

5. CELL-CELL RECOGNITION • Serves as identification tags that are specifically recognized by other cells.

6. ATTACHMENT TO THE CYTOSKELETON & EXTRACELLULAR MATRIX (ECM) • Protein adhere to ECM can coordinate extracellular and intracellular change.

ATTACHMENT TO THE CYTOSKELETON & EXTRACELLULAR MATRIX (ECM) •Bonded microfilaments or other element of cytoskeleton to the protein membrane. •Helps to maintain cell shape and stabilizes the location of certain protein membrane.

Role of membrane carbohydrates in cell-cell recognition •Carbohydrate side chains are found only on the outer surface of the plasma membrane, which form : -glycoprotein when it combined with protein. -glycolipid when it combined with lipid.

Functions of glycolipid & glycoprotein:• Cell recognition/ cell marker Eg: The four human blood type (A,B,AB,O) reflect variation in the carbohydrates on the surface of RBC. •Receptor sites for chemical signal. Eg: Hormones

Cell-cell recognition • A cell’s ability to distinguish one type of neighboring cell from another, is crucial to the functioning of an organism. • Basis for rejection of foreign cells by the immune system. • The way cells recognize other cells is by binding to surface molecules, often carbohydrates on the plasma membrane.

The Fluidity of Membranes • 1. Phospholipids - can move within the bilayer either by lateral movement or flip-flop (rare)

Lateral movement (~107 times per second) (a) Movement of phospholipids

Flip-flop (~ once per month)

• 2. The type of hydrocarbon tails in phospholipids affects the fluidity of the plasma membrane Fluid

Unsaturated hydrocarbon tails with kinks

(b) Membrane fluidity

Figure 7.5 B

Viscous

Saturated hydroCarbon tails

The membrane remains fluid to a lower temperature if it is rich in phospholipids with unsaturated hydrocarbon tails Because of kinks in the tails where double bonds are located, unsaturated hydrocarbons do not pack together as closely as saturated hydrocarbons, and this makes the membrane more fluid Fluid

Unsaturated hydrocarbon tails with kinks (b) Membrane fluidity

Viscous

Saturated hydroCarbon tails

• 3. The steroid cholesterol –Has different effects on membrane fluidity at different temperatures

Cholesterol Cholesterol within the animal cell membrane

• At 37 C of human (relatively warm temperatures), 0

cholesterol makes the membrane less fluid by restraining the movement of phospholipids • Cholesterol also hinders close packaging of phospholipids where it lowers the temperature required for the membrane to solidify

Cholesterol Cholesterol within the animal cell membrane

•Membrane must be fluid to work properly •The functions of cholesterol: a. Cholesterol can be thought as a “temperature buffer” for the membrane fluidity, resisting changes in membrane fluidity that can be caused by changes in temperature

b. Give mechanical stability

Functions of the plasma membrane • Membrane define boundaries and serve as permeability barriers • Membranes are sites of specific functions • Provide for and regulate transport processes • Contain the receptors needed to detect external signals • Provide mechanisms for cell to cell , communication and adhesion

Membrane define boundaries and serve as permeability barriers •Separate the contents of cells from their external environments. •As a selective barrier that allows sufficient age of oxygen, nutrients and wastes products.

Membranes are sites of specific functions • The localization of specific functions is exemplified by many enzymes that are present in or on membranes of organelles • To compartmentalise the organelles within a cell to allow specialized metabolic process to occur.

Provide for and regulate transport processes • Substances into and out of cells and their organelles

(c Contain the receptors needed to detect external signals • The external messenger (signal) may cause a conformational change in the protein that relays the message to the inside of the cell.

Hormone or external message

Provide mechanisms for cell to cell , communication and adhesion • Membrane mediate cell-to-cell communication • Communication between adjacent cells