Unit i cell structure and function 2008

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UNIT I: STRUCTURE AND UNIT I: STRUCTURE AND FUNCTION OF THE CELLFUNCTION OF THE CELL

Mw. Muki (Msc NMH,BSc N,DHPEd, Mw. Muki (Msc NMH,BSc N,DHPEd, RN)RN)

Assistant LecturerAssistant Lecturer

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THEMES TO BE COVEREDTHEMES TO BE COVERED1.1. Eukaryotic and Prokaryotic cellsEukaryotic and Prokaryotic cells2.2. Parts of the cell (Mosaic Model)Parts of the cell (Mosaic Model)3.3. Plasma membrane structure and Plasma membrane structure and

permeabilitypermeability4.4. Membrane proteins and their Membrane proteins and their

functionfunction5.5. Cytoplasm, organelles and their Cytoplasm, organelles and their

functionfunction6.6. The nucleus, structure and The nucleus, structure and

functionfunction

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Definition of cellDefinition of cell

Cell is the basic unit of structure Cell is the basic unit of structure and reproduction for all organism.and reproduction for all organism.

There two types of cells that areThere two types of cells that are Prokaryotic cellsProkaryotic cells Eukaryotic cellsEukaryotic cells

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TOPIC I: EUKARYOTIC & TOPIC I: EUKARYOTIC & PROKARYOTIC CELLSPROKARYOTIC CELLS Cells over millions of years, have Cells over millions of years, have

developed two basic structuresdeveloped two basic structures Prokaryotic cellsProkaryotic cells are cells that are cells that have nohave no

nucleusnucleus ( also called Prokaryotes)( also called Prokaryotes) These include unicellular organisms such as These include unicellular organisms such as

BacteriaBacteria They are generally very small cellsThey are generally very small cells They are the earliest forms of life and still They are the earliest forms of life and still

the most abundant which evolved about 4 the most abundant which evolved about 4 billion years ago.billion years ago.

Some species are highly evolved pathogensSome species are highly evolved pathogens

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Eukaryotic cellsEukaryotic cells are cells are cells having a having a nucleusnucleus ( also spelled Eucaryotes) ( also spelled Eucaryotes)– Eukaryotic cells are seen in Eukaryotic cells are seen in animals, animals,

PlantsPlants, , Fungi Fungi and and ProtistsProtists– Some of the Eucaryotes are Some of the Eucaryotes are unicellularunicellular

while the majority are while the majority are multi-cellularmulti-cellular– Eucaryotes evolved later about Eucaryotes evolved later about 1 billion1 billion

years ago.years ago.– The sizes of Eucaryotes vary from the The sizes of Eucaryotes vary from the

tiny size of tiny size of yeastyeast to the size of an to the size of an elephantelephant and and dinosaurs.dinosaurs.

We are concerned with the study of We are concerned with the study of eukaryotic cells which make up the human eukaryotic cells which make up the human bodybody

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EUKARYOTIC CELL EUKARYOTIC CELL STRUCTURESSTRUCTURES

Eukaryotic cells are organized Eukaryotic cells are organized into different into different compartments. compartments.

All compartments are bounded by All compartments are bounded by membranes. membranes.

For simplicity, we divide the cell For simplicity, we divide the cell into three main compartments: into three main compartments: 1. 1. cell membrane, 2. cytoplasm and cell membrane, 2. cytoplasm and the 3. nucleus.the 3. nucleus.

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CytoplasmCytoplasm is a central metabolic is a central metabolic compartment, bounded by the cell compartment, bounded by the cell membrane.membrane.

Other compartments Other compartments inside inside cytoplasmcytoplasm are called are called organellesorganelles

Compartmentation allows Compartmentation allows specialized specialized functionsfunctions to be carried out in to be carried out in different locations of the cell.different locations of the cell.

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1. THE CYTOPLASM1. THE CYTOPLASM Generally, the cytoplasm:Generally, the cytoplasm:

is the is the site of protein synthesissite of protein synthesis and and many many metabolic processesmetabolic processes..

Contains many Contains many ribosomes,ribosomes, particles particles on whichon which proteins are synthesizedproteins are synthesized

Contains many enzymes for Contains many enzymes for metabolismmetabolism in generalin general

Is a compartment in which Is a compartment in which foodstuffs foodstuffs enter and from which enter and from which wastes leavewastes leave cell cell

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CytoplasmCytoplasm contains fiber of the contains fiber of the cytoskeletal systemcytoskeletal system, which organize , which organize cytoplasmic structure cytoplasmic structure

Contains many different Contains many different organelles organelles

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The The Endomembrane systemEndomembrane system is is involved in moving materials into involved in moving materials into different compartments. It is a set of different compartments. It is a set of interconnected compartments made interconnected compartments made of the of the endoplasmic reticulum (ER),endoplasmic reticulum (ER), Golgi body,Golgi body, Lysosomes,Lysosomes, cell cell membranemembrane. . The cell membrane is The cell membrane is treated separately in this lecture. treated separately in this lecture.

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ENDOPLASMIC RETICULUMENDOPLASMIC RETICULUM

Rough ERRough ER: : synthesizes synthesizes proteinsproteins for for export or movement to different cell export or movement to different cell compartments (but compartments (but notnot to cytoplasm). to cytoplasm).

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Signal hypothesisSignal hypothesis

Certain mRNAsCertain mRNAs encode proteins encode proteins designated for export. These carry a designated for export. These carry a peptide signal at growing end, peptide signal at growing end, causes growing protein to move to causes growing protein to move to ER ER ("docking"),("docking"), insert peptide into insert peptide into membrane, and translocate growing membrane, and translocate growing polypeptide chain across ER polypeptide chain across ER membrane. When protein synthesis membrane. When protein synthesis is complete, polypeptide folds up is complete, polypeptide folds up inside ER, not in cytoplasm. inside ER, not in cytoplasm.

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Smooth ER (sERSmooth ER (sER): ): synthesizes synthesizes lipids, lipids, detoxifies drugsdetoxifies drugs and and poisonspoisons should should

be in bigger amounts in the liver).be in bigger amounts in the liver).

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GOLGI BODYGOLGI BODY

Functions as Functions as intracellular intracellular "post office""post office" for sorting new proteins made on rER. for sorting new proteins made on rER.

Vesicles containing protein pinch off Vesicles containing protein pinch off from ER, fuse with cis face of Golgi. from ER, fuse with cis face of Golgi. Inside Golgi, oligosaccharide chains on Inside Golgi, oligosaccharide chains on proteins are modified. Vesicles pinch off proteins are modified. Vesicles pinch off from trans face of Golgi, carry proteins from trans face of Golgi, carry proteins to several possible destinations: export to several possible destinations: export (out of cell), Lysosomes, Peroxisomes, (out of cell), Lysosomes, Peroxisomes, Cell membrane, etc. Cell membrane, etc.

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LYSOSOMESLYSOSOMES

Compartments where Compartments where old proteins, old proteins, foreign materials, many wastesforeign materials, many wastes are are broken broken

Contain Contain ~40 hydrolytic enzymes~40 hydrolytic enzymes: : lipases, proteases, nucleases, etc. lipases, proteases, nucleases, etc. Break down organic polymers of all Break down organic polymers of all types. types.

"Suicide bags""Suicide bags" if opened up on cell if opened up on cell itself itself = = apoptosisapoptosis. .

Lysosomes Lysosomes are used in are used in Phagocytosis,Phagocytosis, a a process in which foreign materials are process in which foreign materials are brought into the cell and "chewed up". brought into the cell and "chewed up".

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VACUOLESVACUOLES

Large membrane compartments Large membrane compartments Plant cells have especially large Plant cells have especially large

vacuole called the vacuole called the central vacuolecentral vacuole, , can occupy most of the volume of a can occupy most of the volume of a plant cell. plant cell. Storage site of pigments, Storage site of pigments, wastes, water, poisons, and more wastes, water, poisons, and more

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2. THE NUCLEUS2. THE NUCLEUS

Location for DNA & RNA synthesis and Location for DNA & RNA synthesis and protein assemblyprotein assembly

Contains Contains chromatinchromatinss which are which are DNA-DNA-protein complexesprotein complexes. Chromatin can . Chromatin can condense into chromosomes during condense into chromosomes during cell division cell division

Site of Site of RNA synthesisRNA synthesis. 80% of . 80% of RNA RNA are ribosomal RNA.are ribosomal RNA. Remaining Remaining 20% 20% leaves nucleus as t-RNA & m-RNAleaves nucleus as t-RNA & m-RNA, , which direct which direct protein synthesisprotein synthesis

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Contains Contains nucleolus,nucleolus, an an assembly assembly plant for ribosomes.plant for ribosomes. Ribosomal Ribosomal proteins are made in cytoplasm, proteins are made in cytoplasm, must be transported back into must be transported back into nucleus. Ribosomal RNA is made in nucleus. Ribosomal RNA is made in nucleus. These two elements are nucleus. These two elements are integrated inside nucleolus to create integrated inside nucleolus to create ribosomal subunits. These are then ribosomal subunits. These are then exported out of nucleus through exported out of nucleus through nuclear pores. nuclear pores.

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Bounded by Bounded by nuclear membranenuclear membrane. The . The nuclear membrane is a nuclear membrane is a double double layeredlayered structurestructure. It Contains many . It Contains many nuclear poresnuclear pores, which allow material , which allow material to move in and out of nucleus to move in and out of nucleus

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Nuclear PoresNuclear Pores have have octagonal octagonal "doors"doors"" made of protein; open and made of protein; open and close on either side depending on close on either side depending on specific signals. Pore has diameter of specific signals. Pore has diameter of about 10 nanometers (10 x 10-9 m), about 10 nanometers (10 x 10-9 m), smaller than diameter of a complete smaller than diameter of a complete ribosome. Pore can open up to as ribosome. Pore can open up to as much as 26 nm in response to much as 26 nm in response to certain signals. Some signals allow certain signals. Some signals allow motion in but not out, other signals motion in but not out, other signals control reverse transport. control reverse transport.

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Mitochondria Mitochondria are organelles involved are organelles involved in energy transformations and are in energy transformations and are separate from the endomembrane separate from the endomembrane systemsystem

"Energy organelles""Energy organelles" have unique have unique properties: properties:

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are enclosed by are enclosed by double membranedouble membrane systemsystem

contain contain DNADNA and and ribosomesribosomes (70S, not (70S, not 80S like cytoplasmic ribosomes)80S like cytoplasmic ribosomes)

make some of their own proteins make some of their own proteins from their own genesfrom their own genes divide by binary fission (but not divide by binary fission (but not

autonomous, cannot grow or sustain autonomous, cannot grow or sustain life outside of cell)life outside of cell)

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Mitochondria = centers for respiratory Mitochondria = centers for respiratory catabolism.catabolism. Oxygen combined with Oxygen combined with chemicals to break down foods, generate chemicals to break down foods, generate cell energy. Contain outer and inner cell energy. Contain outer and inner compartments, with many membranous compartments, with many membranous cristae that "criss-cross" the internal cristae that "criss-cross" the internal space. space.

Found in virtually every Found in virtually every eukaryotic celleukaryotic cell. . Are small structures similar to bacteria in Are small structures similar to bacteria in

some size. some size.

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3. The cell membrane3. The cell membrane

StructureStructure FunctionFunction

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The cells have a flexible outer The cells have a flexible outer surface called surface called cell membranecell membrane..

SeparatesSeparates the cell’s internal the cell’s internal environment from the external environment from the external environment environment

RegulatesRegulates the flow of material in and the flow of material in and out of the cell maintaining the out of the cell maintaining the appropriate environment for normal appropriate environment for normal cellular activity.cellular activity.

CommunicationCommunication among and between among and between cells and the external environment.cells and the external environment.

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3.1 Structure3.1 Structure

[[A] Membrane lipidsA] Membrane lipids

[B] Membrane proteins[B] Membrane proteins

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3.1.1 Membrane lipids3.1.1 Membrane lipids

75 % are phospholipids75 % are phospholipids 5 % are glycolipids5 % are glycolipids 20 % are cholesterol20 % are cholesterol

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3.1.2 Phospholipids3.1.2 Phospholipids

Description Description Are Are amphipathicamphipathic

Have a Have a hydrophilic hydrophilic polar head and polar head and two two hydrophobic hydrophobic tails.tails.

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3.1.3 Glycolipids3.1.3 Glycolipids

Description Description Are about 5% of Are about 5% of membrane lipids.membrane lipids.

Appear only on Appear only on surface of the surface of the membrane facing membrane facing the exrtacellular the exrtacellular fluid.fluid.

Are target of Are target of attack by attack by bacteria and bacteria and certain toxinscertain toxins

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Glycolipids continuedGlycolipids continued

DescriptioDescription n Found in large Found in large quantities in brain quantities in brain tissuetissue

Contain sugar, Contain sugar, sphingosine, and sphingosine, and a fatty acida fatty acid

No phosphoric No phosphoric acid presentacid present

Bound to cell Bound to cell poisons e.g poisons e.g cholera, tetanus cholera, tetanus toxins.toxins.

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3.1.4 Cholesterol3.1.4 Cholesterol

DescriptionDescription Make about Make about 20% of 20% of membrane membrane lipidslipids

Located among Located among phospholipidsphospholipids

On both sides On both sides of the bilayerof the bilayer

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Cholesterol continuedCholesterol continued

Function Function Provides Provides membrane membrane rigidityrigidity

Prevents Prevents crystallizationcrystallization

Decreases Decreases solubility to solubility to water soluble water soluble molecules.molecules.

Modulates fluid Modulates fluid state of the state of the membranemembrane

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3.2 MEMBRANE PROTEINS3.2 MEMBRANE PROTEINS

Peripheral proteinsPeripheral proteins Integral proteinsIntegral proteins

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3.2.1 Membrane protein functions3.2.1 Membrane protein functions

1.1. ReceptorsReceptors

1.1. CarriersCarriers

1.1. Channel Channel proteinsproteins

Docking sites for Docking sites for specific substancesspecific substances

For specific solutes For specific solutes across membranesacross membranes

Have pores, act as Have pores, act as pumps and gates pumps and gates to selectively move to selectively move specific substances specific substances through the cell through the cell membrane.membrane.

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Membrane protein functionsMembrane protein functions

1.1. Enzymes Enzymes

1.1. Anchoring Anchoring

1.1. recognitionrecognition

Energy Energy transforming transforming enzymesenzymes

Bound to Bound to cytoskeletoncytoskeleton

E.g. many E.g. many glycoproteins.glycoproteins.

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ReferenceReference

Tortora G.J & Derrickson B. Tortora G.J & Derrickson B. (2006) (2006) Principles of Anatomy Principles of Anatomy and Physiologyand Physiology (11th ed.) John (11th ed.) John Wiley & Sons Inc. NY. Chap 3.Wiley & Sons Inc. NY. Chap 3.

Apps D.K Apps D.K et all et all (1992) (1992) BiochemistryBiochemistry

(5(5thth ed),Bailliere Tindall, Londan ed),Bailliere Tindall, Londan