Lecture 4
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Transcript of Lecture 4
Lecture 4: Cell Theory, Structure and Function
Covers 4.1, 4.2, 4.3, 5.1
Cell Theory
• Our current understanding of cell theory is the result of hundreds of years of research on animal and plant material.
• Three basic tenets:*– Every living organism is made up of one or more cells– The smallest living organisms are single cells and cells
are the functional units of multicellular organisms– All cells arise from preexisting cells (and all cells are
derived from common ancestors. Ex: we come from 1 cell, but have hair cells, liver cells, heart cells, etc)
mitochondrion
cytoplasmicfluid
flagellum
vesicle
ribosomeson rough ER
centriole
intermediatefilaments(cytoskeleton)
Golgiapparatus
cytoplasm
lysosome
exocytosis ofmaterial fromthe cell
polyribosome
nuclear pore
basal body
nuclear envelope
chromatin (DNA)nucleolus
nucleus
plasmamembrane
roughendoplasmicreticulum
free ribosome
smoothendoplasmicreticulum
micro- (cytoskeleton)tubules
microfilaments
Fig. 4-3
Fig. 4-4
centralvacuole
cytoplasmic fluid plastid
vesicle
lysosome
cytoplasm
plasmodesmatacell wall plasma
membrane
intermediatefilaments(cytoskeleton)
free ribosome
ribosomesnucleus
nucleolus
nuclear porechromatin
nuclear envelope
smoothendoplasmicreticulum
roughendoplasmicreticulum
Golgi apparatus
chloroplast
mitochondrion
microtubules(cytoskeleton)
cell walls of adjoiningplant cells
Functions of Cells*
• To survive, cells must– Obtain energy and nutrients from environment– Synthesize a variety of proteins and other
molecules necessary for growth and repair– Eliminate waste– Reproduce
Common Features*
• 1.) Plasma membrane
• 2.) All cells contain cytoplasm
• 3.) All cells use DNA as hereditary blueprint
• 4.) All cells obtain raw materials and energy from their environment
1.) PLASMA MEMBRANE*
• Every cell surrounded by thin, rather fluid membrane called plasma membrane
• Proteins in a “sea” of phospholipids• Functions:
– Isolates inside of cell from external environment (phospholipids)
– Regulates flow of material in and out of cell (proteins in the membrane allow exchange of material)
– Allows communication and interaction between cells and with the external environment (proteins in the membrane allow for communication/interaction)
Structure of Plasma Membrane-phospholipids
• Called the phospholipid bilayer, this part of the membrane is composed of 2 layers of phospholipids stacked together
• Each phospholipid has a polar hydrophilic head and two non-polar, hydrophobic tails
• Outside layer has heads pointing to outside of cell with tails facing inside
• Inside layer has tails facing out and heads facing in
• Hydrophilic heads interact with watery contents inside and outside the cell while hydrophobic tails face each other in the middle of the membrane, keeping water out
• Bilayer is fluid; it can move, change shape
head(hydrophilic)
tails(hydrophobic)
A Phospholipid
Fig. 5-2
Phospholipid Bilayer
Structure of Plasma Membrane-proteins
• Called the “fluid mosaic” model, proteins exist in a “sea” of phospholipids
• They are embedded within the phospholipid layers
• There are many types of proteins embedded in the cell membrane
Proteins in plasma membrane
•
Types of proteins in plasma membrane*
• Receptor proteins: trigger cell response when molecules (from other cells) attach to receptor proteins ex: hormones
• Recognition proteins: glycoproteins (protein with sugar component) that are identification tags on the outside of a cell
• Transport proteins: allow hydrophilic molecules to move into the cell. TWO TYPES:– Channel proteins: make channels for molecules to
move through the protein and into the cell– Carrier proteins: attach to molecules on outside of cell
and move them through to the inside
Fig. 5-5
receptor
hormone
(cytoplasm)
(extracellular fluid)
A hormone bindsto the receptor
Hormone bindingactivates the receptor,changing its shape The activated receptor
stimulates a responsein the cell
1
2
3
•
The whole picture
•
Movement of material across plasma membrane
• Due to phospholipids, water-soluble substances CANNOT cross the hydrophobic portion of the plasma membrane (salts, amino acids, sugars)
• However, very SMALL molecules can cross (water, O2, CO2)
• Hydrophobic molecules can cross
2.) CYTOPLASM
• All fluid and structures that lie inside plasma membrane but outside of nucleus
• Contains water, salt, and organic molecules (proteins, sugars, lipids, amino acids, nucleotides)
3.) DNA AS HEREDITARY BLUEPRINT
• More in lecture 8
• Each cell stores all of the genetic material needed to make exact copies of itself
• During cell division, DNA is copied and a complete copy of that DNA is given to the new cell.
4.) OBTAIN MATERIALS AND ENERGY FROM ENVIRONMENT
• More in lecture 5
• Cells must continually acquire and expend energy to live.
2 types of cells*
• Procaryotic (no nucleus)
• Eucaryotic (have a nucleus)
Characteristics of eucaryotic cells*
• Larger than procaryotic• Cytoplasm contains many organelles
– elaborate system of membranes– membrane enclosed structures that perform specific
functions • Contain cytoskeleton (protein fibers that help it maintain
its shape)• Some have cell walls• Some have cilia/flagella• Nucleus is control center of cell
CYTOPLASM: MEMBRANE SYSTEMS
• Three types of membrane systems create internal compartments housing specialized machinery. This separates different reactions that must occur. Material can be moved between these compartments via vesicles (membrane sacs)– Endoplasmic Reticulum*– Golgi Apparatus*– Lysosomes*
Endoplasmic Reticulum (ER)
• Series of interconneted membranes that form sacs and channels in cytoplasm
• PROTEINS AND PHOSPHOLIPIDS ARE MADE HERE*
• Move through ER structure and are modified (folded into final protein shape, sometimes chemically modified)
• Then they accumulate in pockets of ER membrane which bud off as vesicles and are carried to Golgi apparatus
GOLGI APPARATUS
• Set of membranes derived from ER• Stack of interconnected sacs• Modify, sort and package proteins made
in ER (large proteins cleaved into smaller pieces, carbohydrates added to proteins)
• Modified proteins bud off golgi surface and deliver finished products to other parts of cell or to surface to leave cell.
Fig. 4-13
Vesicles merge with theplasma membrane andrelease antibodies into theextracellular fluid
Vesicles fuse with theGolgi apparatus, andcarbohydrates are addedas the protein passesthrough the compartments
The protein ispackaged into vesiclesand travels to the Golgiapparatus
Antibody protein issynthesized on ribosomesand is transported intochannels of the rough ER
Completed glycoproteinantibodies are packagedinto vesicles on the oppositeside of the Golgi apparatus
(extracellular fluid)
(cytoplasm)
vesicles
Golgi apparatus
formingvesicle
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4
3
2
1
Lysosomes
• Membrane-enclosed vesicles that contain digestive enzymes
• Enzymes break food down into small molecules (amino acids, monosaccharides) that can be used by the cell for food
• Lysosomes can also digest worn out organelles, recycling the basic components to be re-used
Fig. 4-14
Golgi apparatus
digestiveenzymes
lysosome
food vacuoles
The Golgiapparatus modifiesthe enzymes asthey pass throughits compartments
The enzymesare packaged intolysosomes, whichbud from theGolgi apparatus
food(extracellular fluid)
Digestiveenzymes aresynthesized onribosomes andtravel throughthe rough ER
(cytoplasm)
The enzymesare packaged intovesicles and travel tothe Golgi apparatus
A lysosome fuseswith a food vacuole,and the enzymesdigest the food
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4
3
2
1
CYTOPLASM-ORGANELLES
• Mitochondria are double-membraned organelles that extract energy from food molecules and package it into ATP, which can be used by the cell.
• Mitochondria exist in large numbers in some cells (where lots of energy needed-muscle) and smaller numbers in other cells (cartilage, for instance)
– More about production of ATP in Lecture 7– Chloroplasts are the “mitochondria” of plant cells. More in Lecture 22
• Many other organelles:– Nucleus– Nucleolus– Peroxisome– Ribosome
•
CELL WALLS
• Some eucaryotic cells have non-living, stiff coatings called cell walls
• Support and protect plasma membrane
• Ex: single celled marine organisms, plants
Fig. 4-4
centralvacuole
cytoplasmic fluid plastid
vesicle
lysosome
cytoplasm
plasmodesmatacell wall plasma
membrane
intermediatefilaments(cytoskeleton)
free ribosome
ribosomesnucleus
nucleolus
nuclear porechromatin
nuclear envelope
smoothendoplasmicreticulum
roughendoplasmicreticulum
Golgi apparatus
chloroplast
mitochondrion
microtubules(cytoskeleton)
cell walls of adjoiningplant cells
CILIA/FLAGELLA
• Extensions of plasma membrane which allow the cell to move
• Ex of cilia: fallopian tubes of female mammals, respiratory tract of land mammals
• Ex of flagella: sperm
How Cilia and Flagella Move
Fig. 4-7
return stroke
cilia liningtrachea
flagellum ofhuman sperm
surface ofhuman eggcell
(a) Cilium
continuous propulsion
plasma membrane
direction of locomotion
power stroke
(b) Flagellum
propulsion of fluid
propulsion of fluid
NUCLEUS-Control Center
• More in Lecture 8