chapter 3 the cellular level of organization. a generalized cell: animal model 1. plasma membrane 2....
TRANSCRIPT
Chapter 3 The Cellular Level of
Organization
A Generalized Cell: Animal Model1. Plasma membrane
2. Cytoplasm
3. Nucleus
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A Generalized Cell
1. Plasma membrane forms the cell’s outer boundary separates the cell’s internal environment from
the outside environment is a selective barrier plays a role in cellular communication
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A Generalized Cell
2. Cytoplasm all the cellular contents between the plasma
membrane and the nucleus cytosol: the fluid portion, mostly water organelles: sub-cellular structures having
characteristic shapes and specific functions
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A Generalized Cell
3. Nucleus large organelle that contains DNA contains chromosomes, each of which
consists of a single molecule of DNA and associated proteins
a chromosome contains thousands of hereditary units called genes
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Plasma Membrane
Flexible yet sturdy barrier The fluid mosaic model - the arrangement of
molecules within the membrane resembles a sea of lipids containing many types of proteins Fluid inside of bilayer consistency of olive oil Mosaic of proteins
The lipids act as a selective barrier to certain substances
The proteins act as “gatekeepers” to certain molecules and ions
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Structure of a Membrane
Consists of a lipid bilayer – made up of phospholipids (amphipathic), cholesterol and glycolipids
Integral/transmembrane proteins – extend into or through the lipid bilayer; most integral proteins, span the entire lipid bilayer
Peripheral proteins - attached to the inner or outer surface of the membrane, do not extend through it
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Structure of a Membrane
Glycoproteins – membrane proteins with a carbohydrate group attached that protrudes into the extracellular fluid
Glycocalyx – the “sugary coating” surrounding the membrane made up of the carbohydrate portions of the glycolipids and glycoproteins Self recognition Immune response - foreign antigens Adherence Protection Hydrophilic – attracting water
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Structure of the Plasma Membrane
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Functions of Membrane Proteins Some integral proteins are ion channels Transporters – selectively move substances
through the membrane Receptors – for cellular recognition; a ligand
is a molecule that binds with a receptor Enzymes - catalyze chemical reactions Others act as cell-identity markers (blood
groups ABO) Attachment to neighboring cells
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Selective Membrane Permeability The cell’s membrane is either permeable or
impermeable to certain substances The lipid bilayer is permeable to oxygen,
carbon dioxide, water and steroids, but impermeable to glucose
Transmembrane proteins act as channels and transporters to assist the entrance of certain substances, for example, glucose and ions
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Passive vs. Active Processes
Passive:1. substances move across cell membranes
without the input of any energy2. with or down the gradient3. lipid soluble
Active:1. energy usually from hydrolysis of ATP2. carrier protein3. gradient independent usually against a
concentration gradient
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Diffusion
Factors affecting diffusion:
Steepness of concentration gradient
Temperature Mass of diffusing substance Surface area Diffusion distance Can substance readily cross
membrane?
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Simple Diffusion
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Osmosis Net movement of water through a
selectively permeable membrane from an area of high concentration of water (lower concentration of solutes) to one of lower concentration of water
Water can pass through plasma membrane in 2 ways:
1. through lipid bilayer by simple diffusion2. through aquaporins, integral membrane
proteins
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Tonicity
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Active Transport
Solutes are transported across plasma membranes with the use of energy
Gradient independent: from an area of lower concentration to an area of higher concentration
Carrier molecule / protein Example: sodium – potassium pump
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Transport in Vesicles
Vesicle - a small spherical sac formed by budding off from a membrane
Endocytosis - materials move into a cell in a vesicle formed from the plasma membrane 1. receptor-mediated endocytosis 2. Phagocytosis3. bulk-phase endocytosis (pinocytosis)
Exocytosis - vesicles fuse with the plasma membrane, releasing their contents into the extracellular fluid
Transcytosis - a combination of endocytosis and exocytosis
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Organelles
Ribosomes - sites of protein synthesis Endoplasmic reticulum - network of membranes in
the shape of flattened sacs or tubules Rough ER – connected to the nuclear
envelope, a series of flattened sacs, surface is studded with ribosomes, produces various proteins
Smooth ER – a network of membrane bound tubules without ribosomes, synthesizes fatty acids and steroids, detoxifies certain drugs, and stores calcium
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Endoplasmic Reticulum
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Organelles
Golgi complex - consists of 3-20 flattened, membranous sacs called cisternae
- modify, sort, and package proteins for transport to different destinations
- proteins are transported by various vesicles
Lysosomes - vesicles that form from the Golgi complex, contain powerful digestive enzymes
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Golgi Complex
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Organelles Mitochondria - the “powerhouses” of the cell
Generate ATP More prevalent in physiologically active cells:
muscles, liver and kidneys Inner and outer mitochondrial membranes Cristae - the series of folds of the inner
membrane Matrix - the large central fluid-filled cavity Self-replicate during times of increased cellular
demand or before cell division
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Mitochondria
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Organelles
Nucleus Spherical or oval shaped structure Usually most prominent feature of a cell Nuclear envelope – a double membrane that
separates the nucleus from the cytoplasm Nuclear pores – numerous openings in the nuclear
envelope, control movement of substances between nucleus and cytoplasm
Nucleolus – spherical body that produces ribosomes Genes – are the cell’s hereditary units, control
activities and structure of the cell Chromosomes – long molecules of DNA combined
with protein molecules
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End of Chapter 3
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