Download Chapter 3: cells

Chapter 3: Cells
Red Blood Cell
White Blood Cell
The Cell
•There are about 200 different types of cells in the human body.
•Muscle cells
•Nerve cells
•Skin cells
•All cells arise from preexisting cells by the process of cell division.
•Cells are the basic structural and functional unit of all living things.
A Generalized View of the Cell
•The cell can be divided into three main parts:
•Plasma membrane
•Separates the internal and external portions of the cell.
•Cytoplasm
•Cytosol – the fluid portion of the cytoplasm. It consists of
water and multiple dissolved substances.
•Organelles – sub-cellular structures that each have a
distinct shape and function.
The Plasma Membrane
•The plasma membrane is composed of:
•Glycoproteins
•Phospholipids
•The membrane is a bilayer of phospholipids.
•The internal layer is formed because of the aggregation of the
hydrophobic tails of the phospholipids.
•The hydrophilic heads can interact with the aqueous
environment of the intracellular and extracellular fluid and
therefore face out.
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Membrane Proteins
•There are two types of proteins in the membrane:
•Peripheral proteins – loosely attached to the interior or the
exterior of the cell.
•These proteins usually act to anchor the cell to other cells
or to anchor organelles inside the cell.
•Integral proteins – span the entire membrane.
•These proteins usually aid in transporting large molecule or
polar molecules across the cell membrane.
•They are also used as receptors for molecules like
hormones.
Integral Proteins
Selective Permeability
•The membrane is selectively permeable, meaning it regulates the
molecules that enter and leave the cell.
•Some molecules can move directly between the phospholipids.
•Lipids, non-polar molecules, small molecules, steroids, O2, and
CO2.
•Some molecules cannot move directly through the phospholipids.
•Ionic compounds, polar molecules, and very large molecules.
•These molecules require integral proteins called carrier
proteins to assist them in moving across the membrane.
•Carrier Proteins come in two forms:
•Channel proteins
•Transporter proteins
Transport Across the Plasma Membrane
•Materials are constantly moving between the aqueous solutions of
the interior of the cell and the exterior of the cell.
•Intracellular fluid (ICF) – this is the cytosol of the cell.
•Extracellular fluid (ECF) – interstitial fluid, plasma, lymph.
•Interstitial fluid – all cells must be bathed by an aqueous
solution. This fluid surrounds all the cells in the microscopic
spaces between the cells.
•Plasma – the aqueous portion of the blood.
•Materials can either move with their concentration gradient or
against it.
•Passive transport – molecules move WITH or DOWN the
gradient: they move from an area of HIGH concentration TO an
area of LOW concentration. This movement requires no ATP.
•Diffusion and osmosis are examples of passive transport.
•Active transport – molecules move AGAINST the gradient: they
move from an area of LOW concentration TO an area of HIGH
concentration with the use of ATP.
•Endocytosis and exocytosis are examples of active transport
Types of Diffusion
•Materials that move via diffusion will eventually reach dynamic
equilibrium, where the net movement of particles is 0 in any given
direction.
•The diagram illustrates a
model of simple diffusion. In
a cell, the substances would
diffuse directly through the
phospholipid bilayer or
through a channel protein.
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•Molecules that are capable of simple diffusion
include:
•Non-polar molecules, lipid-soluble molecules, O2,
CO2, steroid hormones, fat-soluble vitamins. These
molecules diffuse directly through the membrane.
•Water, Na+, Cl-, Ca2+. These molecules use channel
proteins to diffuse.
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•Facilitated diffusion – some materials require a specific channel
protein to move across the membrane. The substance still moves
down its concentration gradient without the use of ATP.
•Materials that move by facilitated diffusion include:
•Glucose, fructose, galactose, water, and some vitamins.
Glucose movement:
1. Glucose binds to a glucose-transporter protein on the
outside of the membrane.
2. The transporter undergoes a change in shape, moving
glucose through the membrane.
3. Glucose is released on the other side of the membrane.
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Osmosis
•Osmosis – the net movement of water from an area of HIGH
concentration TO an area of LOW concentration.
•Osmotic pressure – if a solution contains solute particles that
cannot pass through the membrane, water will move from an area
of lower solute concentration to an area of higher solute
concentration.
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Types of Solutions
•Isotonic solutions – two solutions with the same concentration of
dissolved solute.
•Hypertonic solution - a solution that has a higher solute
concentration with respect to another solution.
•An animal cell placed in a hypertonic solution will lose water
and shrink (crenation).
•Hypotonic solution - a solution that has a lower solute
concentration with respect to another solution.
•An animal cell placed in a hypotonic solution will gain water
and swell, and eventually burst (lyse).
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Active Transport
•Materials are moved against their concentration gradient, from low
concentration to high concentration, with the use of ATP.
•Materials that move in this way use specialized transport proteins
known as pumps.
•Sodium-potassium pump – are required to maintain an unequal
charge between the inside and outside of the cell.
•Cells are usually more negative on the inside.
•This difference can do work and is called a voltage
potential.
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1.
3 sodium ions bind to the pump protein
2.
The protein changes shape due to the bonding of an ATP and releases the sodium
ions into the ECF.
3.
2 potassium ions then bind the protein causing the release of the phosphate
molecule.
4.
The protein resumes the original shape and releases the potassium into the cell.
Transport in Vesicles
•Vesicle – small sac formed from the budding off of an existing
membrane.
•Bulk transport – the movement of larger quantities or mixed
quantities into (endocytosis) or out of (exocytosis) the cell.
•Exocytosis is used to remove waste materials and to secrete cell
products such as hormones, digestive enzymes, and
neurotransmitters.
•Endocytosis
•Phagocytosis – large, solid particles such as whole bacteria and
dead cells are engulfed by cells called phagocytes, a type of
white blood cell.
•This is done by capturing the material with extensions of the
cytoplasm called pseudopods.
•Pinocytosis (bulk-phase endocytosis) – occurs when the cell
membrane invaginates, drawing in a portion of the extracellular
fluid.
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Cytoplasm
•Contains all of the cellular contents between the plasma membrane
and the nucleus; includes the cytosol and the organelles.
•Cytosol – intracellular fluid – fluid portion of the cytoplasm.
•75% to 90% water.
•Contains dissolved solutes, and suspended particles such as
ions, glucose, amino and fatty acids, ATP, and gases.
•Makes up about 55% of the total cell volume.
•Site of most of the chemical reactions in the cell.
Organelles
•Organelles are specialized structures inside the cell that have
characteristic shaped and specific functions.
•Many organelles contain their own specific enzymes.
The Cytoskeleton
•3 types, all made of proteins
•Microfilaments, intermediate filaments, and microtubules.
•The cytoskeleton provides structure and support for the cell
membrane and the other organelles, aids in transport of vesicles,
and increases the surface area through the creation of microvilli
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Centrioles
•Come in pairs.
•Consist of
microtubules made of
the protein tubulin.
•Create the mitotic
spindle, which is
responsible for cell
division.
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Cilia and Flagella
•Both are constructed of
microtubules.
•Cilia are numerous, short,
hair-like projections found lining the surfaces of
body cavities.
•Flagella are longer and are used to move
entire cells.
•The only example of a flagellated human
cell is the male sperm.
Ribosomes
•The sites of protein synthesis.
•Consists of ribosomal RNA and
proteins.
•Have both a large and a small subunit.
•Made in the nucleolus of the cell.
•Can be found floating in the cytosol or
attached to the membranes of
endoplasmic reticulum.
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Endoplasmic Reticulum
•Network of folded membranes.
•Constitutes more than half of the internal membranes in the cell.
•Two types:
•Smooth ER
•Synthesized fatty acids and steroids.
•Detoxifies drugs and poisons.
•Aids in glucose release into the blood stream.
•Has no ribosomes attached to the surface.
•Rough ER
•Contains ribosomes.
•Extends from the nuclear envelope.
•Proteins enter the lumen for processing
and sorting.
•Glycoproteins and phospholipids may be added to proteins to
make membranes.
•Most proteins made here are for secretion from the cell.
Golgi Complex
•Collects proteins synthesized in the rough ER.
•Consists of 3 – 20 cisterns or compartments.
•Proteins arrive at, move through, and leave the Golgi in transport
vesicles.
•Transfer vesicles – move between cisterns.
•Secretory vesicles – move to the plasma membrane.
•Membrane vesicles – add material to the plasma membrane.
•Transport vesicles – carry material to the Golgi and to other
organelles after processing.
•The Golgi complex
•Modifies protein structure.
•Adds sugars to make glycoproteins.
•Adds lipids to make lipoproteins.
•Tags the proteins for their final destination.
•Materials move through the Golgi in one direction.
•Cis to trans.
Lysosomes
•Contain up to 60 different digestive enzymes.
•Lysosomes fuse with vesicles taken in by endocytosis, releasing
the enzymes into the lumen of the vesicle.
•Final products of digestion diffuse into the cytosol.
•Responsible for autophagy, autolysis, and apoptosis.
•Tay-Sachs Disease
•Common among Ashkenazi descent.
•Missing one lysosomal enzyme
•Breaks down a membrane glycolipid called ganglioside GM2.
•Accumulation of this glycolipid causes nerve cell malfunction,
muscle rigidity, blindness, dementia, and premature death.
•The disease is a recessive genetic disorder.
Peroxisomes
•Similar in structure but smaller than lysosomes.
•Contain oxidases – remove hydrogen atoms.
•Oxidize substances like amino acids, lipids, and toxins.
•Very abundant in the liver.
•Byproduct is H2O2 – hydrogen peroxide.
•Catalase – enzyme that breaks down H2O2 onto water and oxygen.
Proteasomes
•Responsible for the continuous destruction of faulty, damaged, or
unnecessary proteins.
•Contain many proteases.
•Found in both the cytosol and the nucleus.
•The residual amino acids can be recycled into new proteins.
Mitochondria
•Site of ATP production.
•Two membranes – inner and outer.
•Inner membrane has many folds called cristae.
•Increases the surface area for ATP production.
•Internal space is called the matrix.