Review of Cells, Organelles and Transport Processes

7/31/2019 Review of Cells, Organelles and Transport Processes

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The Cell

Learning Outcomes:

List 3 main parts of the cell and describe its function

Explain how the plasma membrane is selectively

permeable

Differentiate the various transport processes in a cell

Describe structural components of the cell

Describe the function of the various organelles in thecell


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Overview of the cell


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Part Function

Plasma membrane Selective barrier, regulatemovement of material, cellularcommunication

Cytoplasm Houses all the organelles in awatery liquid called the cytosol

Nucleus Contains genetic material thatcontrols cell structure andfunction


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Glycocalyx - the sugary coating surrounding the membrane made up of the

carbohydrate portions of the glycolipids and glycoproteins

Plasma Membrane


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Functions of Membrane Proteins

Some integral proteins are ion channels

Transporters - selectively movesubstances through the membrane

Receptors - for cellular recognition; aligand is a molecule that binds with areceptor

Enzymes - catalyze chemical reactions

Others act as cell-identity markers


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Membrane Permeability

The cell is either permeable or impermeable to certainsubstances

The lipid bilayer is permeableto oxygen, carbon dioxide,

water and steroids, but impermeableto glucose

Transmembrane proteins act as channels andtransporters to assist the entrance of certain substances,

for example, glucose and ions

Selective permeability establishes gradients


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Passive vs. Active Processes

Passive processes - substances move across cellmembranes without the input of any energy; use thekinetic energyof individual molecules or ions.

Active processes - a cell uses energy, primarily from thebreakdown of ATP, to move a substance across themembrane, i.e., against a concentration gradient


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Passive Processes


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Channel-mediated Facilitated Diffusion ofPotassium ions through a Gated K + Channel


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Carrier-mediated Facilitated Diffusion of Glucoseacross a Plasma Membrane


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Net movement of water through a selectivelypermeable 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 diffusion

2. through aquaporins, integral membrane proteins

Osmosis


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Sources of energy:

1. Hydrolysis of ATP primary active transport

2. Ionic concentration gradient secondary active transport

1

3 Na+ expelled

3 Na+

ADPP

P

2 K+

imported

K+gradient

Na+gradient

Na+/K+ ATPase

Extracellular fluid

Cytosol

2K+

ATP2 3 4

Active Transport


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Symporters: transporters move two substances inthe same direction

Antiporters: transporters move two substances inthe opposite direction


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Transport in Vesicles

Vesicle- a small spherical sac formed by budding off froma membrane

Endocytosis - materials move into a cell in a vesicleformed from the plasma membrane

three types: receptor-mediated endocytosisphagocytosisbulk-phase endocytosis (pinocytosis)

Exocytosis - vesicles fuse with the plasma membrane,releasing their contents into the extracellular fluid


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Receptor-

MediatedEndocytosis Selective uptake of

materials needed

by the cell


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Phagocytosis Main way to getrid of large, solidparticles

Macrophages in

tissues Neutrophils in

blood


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Copyright 2009 John Wiley & Sons, Inc.

Pinocytosis


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Exocytosis releases material from the cell, especiallyimportant for:

1. Secretory cells

2. Nerve cells

Surface area ofplasma membrane iskept relativelyconstant by

endocytosis versusexocytosis


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Cytoplasm - 2 components

1. Cytosol - intracellular fluid, surrounds the organelles- the site of many chemical reactions- energy is usually released by these reactions- reactions provide the building blocks for cell maintenance, structure,function and growth

The cytoskeleton - network of protein filaments throughout the cytosol-provides structural support for the cell-three types according to increasing size: microfilaments, intermediatefilaments, and microtubules

2. OrganellesSpecialized structures within the cell


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The Cytoskeleton

Movement &mechanical support

Stabilise position of

organelles and cellattachment

Determine cellshape andmovement oforganelles


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Ribosomes- sites ofproteinsynthesis


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Endoplasmic reticulum - networkof membranes in the shape of

flattened sacs or tubules

-Rough ER -connected to thenuclear envelope, a series offlattened sacs, surface is studdedwith ribosomes, produces various

proteins

-Smooth ER- a network ofmembrane tubules, does not haveribosomes, synthesizes fatty acidsand steroids, detoxifies certain

drugs


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Golgi Complex

consists of 3-20 flattened, membranous sacs calledcisternae


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Peroxisomes - smaller thanlysosomes, detoxify severaltoxic substances such asalcohol, abundant in the liver

Proteasomes - continuouslydestroy unneeded, damaged, orfaulty proteins, found in the

cytosol and the nucleus


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Mitochondria - the powerhouses of the cell - Generate ATPMore prevalent in physiologically active cells: muscles, liver and kidneysSelf-replicate during times of increased cellular demand or before celldivision


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Nuclear envelope - a double membrane that separates the nucleus from thecytoplasm

Nuclear pores - numerous openings in the nuclear envelope, controlmovement of substances between nucleus and cytoplasm

Nucleolus - spherical body that produces ribosomes

Nucleus


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Copyright 2009 John Wiley & Sons, Inc.


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Review DNA Replication

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Review of Cells, Organelles and Transport Processes