Chapter 3 û Cells

8/8/2019 Chapter 3 Cells

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Chapter 3 Cells (pg. 65-88) Notes

Cell - is normally made up of four primary elements oxygen, carbon, hydrogen and

nitrogen plus much smaller amounts of several other elements.- Although the 4 major elements build most of the cells structure (which is

largely protein), the trace elements are very important for certain cellfunctions. For example, calcium is needed for blood clotting (among otherthings), and iron is necessary to make hemoglobin, which carries oxygen in

the blood. Iodine is required to make the thyroid hormone that controls

metabolism. In their ionic form, many of the metals (such as calcium,sodium, and potassium) can carry an electrical charge; when they do they

are called electrolytes.- Living cells made up of at least 60% of water. All body cells are constantly

bathed in a dilute saltwater solution (something like seawater) called

interstitial fluid,which is derived from the blood.

Anatomy of a Generalized Cell

Although no one cell type is exactly like all the others, cells do have the same basic parts,and there are certain functions common to allcells.

Cells are organized into three main regions

Nucleus Cytoplasm Plasma membrane

a) Orientation diagram: The 3 main regions of the generalized cell.b) Structure of the nucleus.

The nucleus is usually located near the center of the cell. It is surrounded by the semifluid

cytoplasm, which in turn is enclosed by theplasma membrane , which forms the outer cellboundary.


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Structure of the Generalized Cell. No cell is exactly like this one, but this generalized cell drawing illustrates features common to many

human cells.

The Nucleus the control center or headquarters of a cell. Contains genetic material ordeoxyribonucleic acid(DNA).

DNA - is much like a blueprint that contains all the instructionsneeded for building the whole body.

Have instructions for building proteins. Absolutely necessary for cell reproduction.

- Usually shapes like how the cell shapes.- Has three recognizable regions or structuresNuclear Envelope

o A double membrane barrier called nuclear envelope or nuclear membranebinds the nucleus.

o Between the two membranes is a fluid-filled moat, or space.o Contain nuclear pores that allow for exchange of material with the rest of

the cell.

o Selectively permeable, but substances pass through it much more freelybecause of its large pores.

o Encloses a jellylike fluid called nucleoplasm in which other nuclearelements are suspended.


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Nucleoli

o Nucleus contains one or more nucleoli.o Sites ofribosome production.o Ribosomes then migrate to the cytoplasm through nuclear pores, which

serve as the actual site of protein synthesis.

Chromatin

o Composed of DNA and protein that is scattered throughout the nucleus.o Chromatin condenses to form chromosomes (structure that contains DNA

and proteins) when the cell divides.

Plasma Membrane

y Is a fragile, transparent barrier that contains the cell contents and separates themfrom the surrounding environment (normally called cell membrane).

y Consists of2 lipid (fat) layers arranged tail to tail in which protein molecules float.y Most of lipid portion isphospholipids (some with attached sugar groups), but a

substantial amount ofcholesterolis also found.

y Hydrophilicheads (water loving) are phospholipid molecules and are attracted towater, the main component of both the intercellular and extracellular fluids, and so

they lie on both the inner and outer surfaces of the membrane.

y Hydrophobic tails (water hating) avoid water, and line up in the center of themembrane.

y The phospholipids allow biological membranes to reseal themselves when torn.y The hydrophobic makeup of membrane interior makes the plasma membrane

impermeable to most water-soluble molecules. The cholesterol helps keep the

membrane fluid.

Structure of the Plasma Membrane


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Proteins

- Scattered in the lipid bilayer- Responsible for most of the specialized functions of the membrane- Some are enzymes- Many of them protruding from the cell exterior are receptors for hormones or other

chemical messengers or are binding sites for anchoring the cell to fibers or to other

structures inside or outside the cell.- Most that span the membranes are involved in transport functions.- Some cluster together to form protein channels (tinypores) through which water

and small water-soluble molecules or ions can move;- Others act as carriers that bind to a substance and move it through the membrane- Branching sugar groups are attached to most of the proteins abutting the

extracellular space.

- Such sugar proteins are calledglycoprotein and because of their presence, the cellsurface is a fuzzy, sticky, sugar-rich area calledglycocalyx.

- G

lycoproteins determine your blood type, act as receptors that certain bacteria,viruses, or toxins can bind to, and play a role in cell-to-cell interactions.

Plasma Membrane Specialization

Microvilli finger-like projections that greatly increase the cells surface area for

absorption so that the process occurs more quickly.Membrane Junctions vary depending on their roles.

o Tight Junctions impermeable junctions that bind cells togetherinto leakproof sheets that prevent substances from passing

through the extracellular space between cells.o Desmosomes anchoring junctions that prevent cells subjected to

mechanical stress (such as skin cells) from being pulled apart.

o Gap Junctions commonly seen in the heart and betweenembryonic cells. Functions manly to allow communication.Neighboring cells are connected by connexons, which are hollow

cylinders composed of proteins that span the entire width of themembranes.


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Cytoplasm

Material outside the nucleus and inside the plasma membrane It is the site of most cellular activities. The factory area of the cell. Has three major elements: cytosol, organelles and inclusions.Cytosol is a semitransparent fluid that suspends the other elements.

Organelles is the metabolic machinery of the cell. Each type is specialized to carry outa specific function for the cell as a whole.

Inclusions nonfunctioning unit.Most are stored nutrients or cell products.

Cytoplasmic Organelles Little organs that specialized cellular compartments, each performing its own

job to maintain the life of the cell.

Many are bounded by a membrane similar to the plasma membrane M

embrane boundaries of such organelles allow them to maintain an internalenvironment quite different from that of the surrounding cytosol.

Compartmentalization is crucial to their ability to perform their specializedfunctions for the cell.

Mitochondria

Powerhouses of the cell Change shape continuously Carry out reactions where oxygen is used to break down food ProvidesATP (Adenosine Triphosphate) for cellular energy Tiny threadlike or sausage-shaped organelles M

itochondrial wall consists of a double membrane, equal to two plasma membranes,placed side by side Outer membrane is smooth and featureless but inner membrane has shelf like

protrusions called cristae.

Enzymes dissolved in the fluid within the mitochondria, as well as enzymes thatform part of the cristae membranes; carry out the reactions in which oxygen is used

to break down foods.


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Ribosome

Made of protein and RNA (ribonucleic acid) Sites of protein synthesis Found at two locations: Free in the cytoplasm and attached to rough endoplasmic

reticulum.

o Endoplasmic Reticulum a network within the cytoplasm- Fluid-filled tubules for carrying substances- Accounts for about half of a cells membranes.- Serves as a mini-circulatory system for the cell

because it provides a network channels forcarrying substances (mostly proteins) from one

part of cell to another.- Two types ofER

y Rough Endoplasmic Reticulumo Studded with ribosomeso Site where building materials of

cellular membrane are formedy Smooth Endoplasmic Reticulum

o Functions in cholesterol synthesisand breakdown, fat metabolism,

and detoxification of drugs

The Golgi apparatus

Appears as a stack of flattened membranous sacs, associated with swarms of tinyvesicles.

Generally found close to the nucleus The principal traffic director for cellular proteins Major function is to modify and package proteins (sent to it by the rough ER via

transport vesicles) in specific ways, depending on their final destination.

Produces different types of packagesy Secretory vesicles - Vesicle contains proteins destined for

extracellular release

y Cell membrane componentsy Lysosomes - cube shaped organelles that contain enzymes (acid

hydrolases) that break up waste materials and cellular debris. It

functions as the cells demolition sites. They are specially

abundant in phagocytes, the cells that dispose of bacteria and celldebris.

Peroxisomes

Membranous sacs of oxidase enzymes that use molecular oxygeny Detoxify harmful substances (including alcohol and formaldehyde)


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y Break down free radicals(highly reactive chemicals with unpaired electrons that can

scramble the structure of proteins and nucleic acids)

Replicate by pinching in half Specially numerous in liver and kidney cells, which are very active in detoxificationCytoskeleton

Network of protein structures that extend throughout the cytoplasm Provides the cell with an internal framework by acting as the cells bone and muscles. Made up of microtubules, intermediate filaments, and microfilaments

y Intermediate filaments help form desmosomes and provideinternal guy wires to resist pulling forces on the cell.

y Microfilaments are most involved in cell motility and inproducing changes in cell shape.

y Microtubules determine the overall shape of a cell and thedistribution of organelles.

The cytoskeleton. A) In this micrograph of the cytoskeleton of a nerve cell, the microtubules appear green; the microfilaments are blue.

Intermediate filaments form most of the rest of the network. (b-d) Diagrammatic views of cytoskeletal elements.

Centrioles

Lie close to the nucleus Rod-shaped bodies (lie at right angles to each other) made of microtubules Direct formation of mitotic spindle during cell division Some cells have projections called cilia (eyelashes), whiplike cellular extensions that

move substances along the cell surface. When a cell is about to make cilia, its centrioles multiply and then line up beneath the

plasma membrane at the free cell surface. Microtubules then begin to sprout from the

centrioles and put pressure on the membrane, forming the projections. If theprojections formed by the centrioles are substantially longer, they are called flagella

(propels the cell).


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Cell Diversity

1. Cells that connects body parts:y Fibroblast. The elongated shape of this cell lies along the cable-like

fibers that it secretes. It has an abundant rough ER and a largeGolgi apparatus to make and secrete the protein building blocks of

these fibers.y Erythrocyte (redbloodcells). This cell carries oxygen in the

bloodstream. Its concave disk shape provides extra surface areafor the uptake of oxygen and streamlines the cell so it flows easily

through the bloodstream. So much oxygen-carrying pigment is

packed in erythrocytes that all other organelles have been shed tomake room.

2. Cell that covers and lines body organs:y Epithelial cell. The hexagonal shape of this cell is exactly like a

cell in honeycomb of a beehive. This shape allows epithelial cellsto pack together in sheets. An epithelial cell has abundant

intermediate filaments that resist tearing when the epithelium is

rubbed or pulled.

3. Cells that move organs and body parts:y Skeletal muscle andsmooth muscle cells. These cells are elongated

and filled with abundant contractile filaments, so they can shorten

forcefully and move the bones or change the size of internalorgans.


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4. Cell that stores nutrients:y Fat cell. The huge spherical shape of a fat cell is produced by a

large lipid droplet in its cytoplasm.

5. Cell that fights disease:y Macrophage (a phagocytic cell). This cell extends long pseudopods

(false feet) to crawl through tissue to reach infection sites. Themany lysosomes within the cell digest the infectious

microorganisms it takes up.

6. Cell that gathers information and controls body functions:y Nerve cell (neuron). This cell has long processes for receiving

messages and transmitting them to other structures in the body.

The processes are covered with an extensive plasma membrane,and a plentiful rough ER is present to synthesize membrane

components.

7. Cells of reproduction:y Oocyte (female). The largest cell in the body, this egg cell contains

several copies of all organelles, for distribution to the daughter

cells that arise when the fertilized egg divides to become anembryo.

y Sperm (male). This cell is long and streamlined, built for swimmingto the egg for fertilization. Its flagellum acts as a motile whip to

propel the sperm.


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Cell Physiology

Each of the cells internal parts is designed to perform a specific function for the cell. Each cell has the ability to metabolize (use nutrients to build new cell material,

break down substances, and make ATP), digest food,dispose of wastes, reproduce,

grow, move,and respondto a stimulus (irritability).

Membrane Transport

Movement of substance into and out of the cell Asolution is a homogenous mixture of two or more components (e.g. air we breath

which is a mixture of gases, seawater which is a mixture of water and salts). Asolventis the substance present in the largest amount in a solution. (Water is the

bodys chief solvent)

Solutes are the components or substances present in smaller amounts ntracellular fluid is a solution containing small amounts of gases (oxygen and

carbon dioxide), nutrients, and salts, dissolved in water. So too is interstitial fluid,

the fluid that continuously bathes the exterior of our cells. The plasma membrane allows some materials to pass while excluding others This permeability includes movement into and out of the cell Transport is by two basic methods:

o Passive transport No energy is required Diffusion is an important means of passive membrane transport for

every cell of the body. It is the process by which molecules (and ions)move away from a region where they are more concentrated (more

numerous) to a region where they are less concentrated (less

numerous).Particles tend to distribute themselves evenly through a

solution. Speed of diffusion is affected by the size of the molecules(the smaller the faster) and temperature (the warmer the faster).


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y Simple Diffusion: Unassisted process Solutes are lipid-soluble

(fats, fat-soluble vitamins,

oxygen, carbon dioxide)materials or small enough

to pass through membrane

pores

y Osmosis - simple diffusion of water Highly polar water easilycrosses the plasma

membrane and it is repelled

by the (nonpolar) lipid core. Osmosis into and out of

cells is occurring all thetime as water moves down

its concentration gradient

y FacilitatedDiffusion Substances require a

protein carrier for passivetransport (requires kinetic

energy) Provides passage for

certain needed substances

(notably glucose) that areboth lipid-insoluble and too

large to pass through the

membrane pores


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Filtration generally occurs only across capillary walls. It is the processby which water and solutes are forced through a membrane byfluid,or hydrostatic pressure. The blood usually exerts hydrostatic pressure.

y Apressure gradientmust exist Solute-containing fluid is pushed

from a high pressure area to a

lower pressure area

o Active transport The cell must provide metabolic energy Transport substances that are unable to pass by diffusion: They may

be too large, they may not be able to dissolve in the fat core of the

membrane or they may have to move against a concentration gradient Two common forms of active transport:

y Solute pumping similar to the carrier-mediated facilitated diffusion

Amino acids, some sugarsand ions are transported bysolute pumps

ATP energizes proteincarriers, and in most cases,

moves substances against

concentration gradients

The sodium-potassiumpump that simultaneously

carries sodium ion out ofand potassium ions into the

cell is absolutely necessaryfor normal transmission of

impulses by nerve cells.


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Operation of the sodium-potassium pump, a solute pump. ATP provides the energy for a pump protein to move three sodium ions

out of the cell and two potassium ions into the cell. Both ions are moved against their concentration gradients.

y VesicularTransport Some substances cant getthrough the plasmamembrane by passive or by

active transport. It involves help from ATP,

moves into or out of cells

without their actuallycrossing the plasma

membrane.

Exocytosis Moves materials out of thecell Material is carried in a

membranous vesicle

Vesicle migrates to plasmamembrane

Vesicle combines withplasma membrane

Material is emptied to theoutside


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Exocytosis. (a)A secretory vesicle migrates to the plasma membrane, and the tw o membranes fuse. The fused site opens and releases

the contents to the outside of the cell.

Endocytosis Extracellular substances

are engulfed by being

enclosed in a membranousvesicle

Types of endocytosis: Phagocytosis cell eating. A

protective mechanism as itacts as scavenger cells that

police and protects thebody by ingesting bacteria

and other foreign debris.

Pinocytosis cell drinking.It gulps droplets of

extracellular fluid. It is aroutine activity of mostcells.

Cell Life Cycle the series of changes of a cell goes through from the time it is formed until

it divides. Has two major periods: Interphase

o Cell growso Cell carries on metabolic processes Celldivision

o Cell replicates itselfo Function is to produce more cells for growth and repair processes

DNA Replication Genetic material duplicated and readies a cell for division into two cells


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Occurs toward the end of interphase DNA uncoils (nucleotide chains) and each side serves as a template The upright parts of the DNA ladder are alternating phosphate and sugar units, and

the runs of the ladder are made f pairs of nitrogen-containing bases

Replication of the DNA molecule during interphase. The DNA helix unwinds (center), and its n ucleotide strands are separated. Each

strand then acts as a template for building a new complementary strand. As a result, two helixes, each identical to the ori ginal DNA helix,

are formed.

Events of Cell Division

Mitosis

Division of the nucleus Results in the formation of two daughter nuclei with the exact same genes as the

mother nuclei.

Stages of mitosis:o Interphase

y No cell division occurs


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y The cell carries out normal metabolic activity and growtho Prophase

y First part of cell divisiony Chromatin threads coil and shortens so thatchromosomes

appear

y Because DNA has already been replicated, each chromosome isactually made up of two strands called chromatid, heldtogether by a small buttonlike body called centromere.

y Centrioles separate from each other and begin to move towardopposite side of the cell, directing the assembly of a mitotic

spindle between them as they move.

y Centromeres migrate to the poleso Metaphase

y Spindle from centromeres are attached to chromosomes thatare aligned in the center of the cell

o Anaphasey The centromeres that have held the chromatids together split.y Daughter chromosomes are pulled toward the polesy The cell begins to elongate

o Telophasey Daughter nuclei begin formingy A cleavage furrow (for cell division) begins to form


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Cytokinesis

Division of the cytoplasm Usually begins during late anaphase and completes during telophase. Contractile ring made of microfilaments forms a cleavage furrow over the midline of

the spindle, and it eventually squeezes or pinches the original cytoplasmic mass into

two parts (two daughter cells).

Protein Synthesis

Gene DNA segment that carries a blueprint for building one protein Proteins have many functions

o Building materials for cellso Act as enzymes (biological catalysts)

RNA is essential for protein synthesisRole ofRNA

Transfer RNA (tRNA)o Transfers appropriate amino acids to the ribosome for building the protein

Ribosomal RNA (rRNA)o Helps form the ribosomes where proteins are built

Messenger RNAo Carries the instructions for building a protein from the nucleus to the ribosome

Transcription - Transfer of information from DNAs base sequence to the complimentarybase sequence of mRNA

Translation

Base sequence of nucleic acid is translated to an amino acid sequence Amino acids are the building blocks of proteins


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Protein Synthesis. (1)Transcription. (2-5) Translation.

Chapter 3 û Cells

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