EDUCATION

“Education is a progressive discovery of our own ignorance.”

-Will Durant

The Amazing Cell

Chapter 3

Anatomy and Physiology

Cells

• Basic unit of living things.• Can exist alone as a single, free, living plant or

animal, or can combine to form elaborate and complex organisms.

• Multicellular organisms are when cells have differentiated and become grouped into specialized tissues that work collaboratively to sustain life for the animal as a whole.

• We must understand the cell before we can understand the anatomy and physiology of the tissues and systems the cell makes up

Evolution of Cells

• Evolved about 3 billion years ago.• Primitive cells are thought to have resembled

present-day bacteria and contained a single strand of DNA in a gelatinous protoplasm.

• Prokaryotes- “before nucleus”, cells without nucleus were thought to have developed first.• Has DNA but not in a separate compartment

• Eukaryotes- “true nucleus”, developed later and are found in all multicellular organisms.• Has distinct nucleus surrounded by protective

nuclear envelope.

Size Limitations

• Size of most cells is restricted to 10-30 µm in diameter because of relationship between surface area and volume of a cell.

• Why is this important:• Smaller cells can feed themselves efficiently to

carry on functions.• Large cells could not take in nutrients fast

enough to support cell and would therefore die. • Also a small cell is better governed by a single

nucleus. Larger cells need multiple nuclei. • What is an example of this and why?

Mammalian Cell Anatomy

• Contain essential structures:• Cell membrane (also known as plasma

membrane).• Separates cell from environment.

• Cytoplasm• Everything inside the cell membrane

aside from nucleus and genetic material.

• Nucleus• Contains the genetic material of the

cell.

http://www.enchantedlearning.com/subjects/biology/cells/

Other optional parts of a cell

• Cilia• Mitochondria• Endoplasmic Reticulum (ER)• Ribosomes• Golgi apparatus• Lysosome• Peroxisomes

Cell Membrane

• Flexible, elastic barrier between inner cytoplasm and outer environment.

• Contains infoldings and outpouchings that provide extra surface area.• Why is this important?

• Capable of self-repair.• Governs the movement of atoms and

molecules in and out of the cell.• Consists primarily of protein,

phospholipids, cholesterol, lipids, and carbohydrates.

Membrane Structure• Lipid bilayer: composed of two layers of phospholipid molecules

• Hydrophilic “heads” are on outside • Hydrophobic fatty acid “tails” are on

the inside• Most lipid soluble molecules easily

pass through membrane • Water-soluble molecules do not

readily pass through

• Fluid mosaic: Proteins suspended in bilayer and move easily throughout membrane to create a constantly changing pattern

Cell Membrane Structure Continued

• Composed of Structural and Globular proteins.• What are these also called?• What do they do?

• Proteins that occur within the bilayer are called integral proteins. • Globular proteins that span the entire

width of the membrane and may create channels through which other molecules can pass.

Integral Proteins• Channels they create may be:

• Selective• permit only certain molecules in or out of the

cell

• Pores• allow the passage of molecules freely

Peripheral Proteins• Type of globular protein which can be

bound to the inside or outside surfaces of the cell membrane.• Sometimes act as enzymes• May be involved in changing the cell’s

shape (muscle contraction).

Cell Membrane: External Surface • Glycocalyx – coating on the cell surface of some

cells made of glycoprotein and glycolipids.• Unique to each cell – provides markers for

recognition and for interactions.• Composed of 2 groups of molecules:

• Cell Adhesion Molecules (CAMs)• Sticky glycoproteins that cover cell

surface. Help cells move past one another and signaling.

• Signal circulating cells like WBCs to areas of inflammation or infection

• Membrane Receptors• Integral proteins and glycoproteins that

act as binding sites on the cell surface.• Involved with signaling as well.

Flagella and Cilia

• Extensions of the plasma membrane that extend into the extracellular space.

• Both contain 9 pairs of microtubules that encircle a central pair of microtubules.

• Cilia- occur in large numbers on the exposed surface of some cells. Shorter than flagella and move synchronously to create waves of motion for propulsion.• Functions:

• In upper respiratory tract, propel bacteria and mucus from the lungs

• In oviduct, pulls egg from ovary into oviduct.

• Flagella- significantly longer than cilia and usually occur singularly.• Attached to individual cells and aid in

propulsion.• Example:

• Tail of sperm is flagellum

Cytoplasm

• The inner substance of the cell, excluding the nucleus.

• Components include:• Cytosol• Cytoskeleton• Organelles• Inclusions

Cytosol

• The fluid of the cell• Viscous, semi-transparent liquid

composed of dissolved electrolytes, amino acids, and simple sugars.

• Proteins suspended within fluid give fluid its thick, jellylike consistency.• Are enzymes that are important in

metabolic activities of the cell.

Cytoskeleton

• Three dimensional frame for the cells, is neither rigid or permanent.

• Flexible and fibrous and changes in accordance to activities of the cell.

• Gives support and shape to the cell, enables cell to move and provides direction for metabolic activity.

• Also anchors organelles.• Types of fibers that comprise cytoskeleton:

• Microtubules• Intermediate fibers• Microfilaments.

• Microtubules• Thickest fibers and are long and hollow• Form cables that organelles attach too.• Proteins move these organelles along

microtubules throughout cell.• Can be easily disassembled and

reasembled to form new paths or take on new direction.

• Composed of tubulins.

• Intermediate fibers• Woven, ropelike fibers that possess

high tensile strength and are able to resist pulling forces on the cell by acting as internal guy wires.

• Toughest and most permament part of the cytoskeleton.

• Composed of proteins• May take on different names:

• Tonofilaments-in epithelial cells• Neurofilaments- in nerve cells

• Microfilaments• Located near cell surface on the cytoplasmic

side of the plasma membrane and are arranged in bundles and meshworks.

• Composed of actin and myosin• Play key role in cell’s ability to change shape,

break apart during cell division and form outpouchings and involutions.

• Are assembled where and when needed.• Depends on what cell is doing as to how many

are found within cell.

Organelles

• “little organs” • Membrane bound structures within

cytoplasm that have specialized functions.• Is separated from cytoplasm by own

membrane so can maintain own internal environment.

• Compartmentalization is good for metabolic processes such as food absorption, energy production, and excretion.

Organelles continued

• Include:• Mitochondria• Ribosomes• Golgi Apparatus• Endoplasmic Reticulum• Lysosomes• Peroxisomes

http://en.wikipedia.org/wiki/Image:Biological_cell.svg

Mitochondria

• One of largest organelles• Called “powerhouse of the cell” because

produces up to 95% of energy that fuels the cell.

• Nutrient molecules (i.e. glucose) are broken down to produce intracellular fuel.

• Location of many biochemical reactions.• Amino acid and fat catabolism

• Where respiration takes place• What is this?

Mitochondria continued.

• Active cells have higher energy demands so have more mitochondria.• Heart cells

• Mitochondria can divide through fission-or the pinching itself in half. • Tend to be located at portion of cell

where energy requirements are the greatest.

• Contain DNA, RNA and enzymes. • Provide selves with 13 proteins while

nucleus provides the remainder.

Mitochondrial shape

• Tend to be elliptical and round with outer smooth membrane and inner involuted membrane.

• Inner membrane forms cristae which increase internal working area and matrix (enzyme-rich liquid housed in mitochondria).

• Cristae are site of ATP production• what does this do?

Ribosomes

• Most common organelle in the cell.• Made of two globular subunits composed

of protein and rRNA.• Important in protein synthesis.• Can attach and detach from membranes

and move freely within the cell.• Move back and forth depending on type

of protein they are making between endoplasmic reticulum and cytoskeleton.

Endoplasmic Reticulum (ER)

• Series of flattened tubes stacked on one another and bent into crescent shape.

• Composed of single lipid bilayer• May be rough or smooth depending on if it contains

ribosomes or not. • Rough ER is involved in production of protein.• Smooth ER is connected to Rough ER and is

active in synthesis and storage of lipids. • In liver may also break down drugs and

break down glycogen into glucose.

Golgi Apparatus

• Found near nucleus and is similar in structure to ER (composed of cisternae)

• Receives proteins produced by ER.• Proteins are modified here as they move

from fold to fold.• Once completed they are packages in

vesicles and travel out into cell or to cell membrane.

Lysosomes

• Specialized vesicle formed by Golgi apparatus.• Contains hydrolytic enzymes which engulf bacteria

or cell nutrients and digests them.• Principal responsibility to breakdown nutrient

molecules.• Considered “stomach of the cell”.• When cells die, lysosomes are released and digest

other portions of the cell, this is called autolysis.• May also release enzymes outside of cell to assist

with breakdown of extracellular material.

Peroxisomes

• Membranous sacs containing enzymes found throughout the cell.

• Reproduce through fission.• Important in detoxification of various molecules.

• Remove free radicals- normal products of cellular metabolism but can be harmful in large numbers

• Carry two major enzymes:• Peroxidases-assist in conversion in free

radicals to hydrogen peroxide.• Catalases-reduce hydrogen peroxide to water.

Inclusions

• Packaged units of metabolic products or substances that the cell has engulfed.

• May or may not be membrane-bound.• Vacuoles are larger than vesicles but are

of similar structure.

Centrioles

• Small, hollow-like cylinders composed of microtubules.

• Found in pairs perpendicular to one another.

• Visible during cell division near nuclear envelope

• Help to organize spindle fibers during cell division.

• May also form bases of cilia and flagella (basal bodies).

Nucleus

• Largest organelle in the cell.• Control center or “brain” of the cell.• Primary functions are to maintain

hereditary information of the species and to control cellular activities through protein synthesis.

• Some cells may be multi-nucleated while some are anucleated.• What is this and where is it found?• What is a disadvantage to no nucleus?

Nuclear Anatomy

• Divided into four parts:• Nuclear Envelope or membrane• Nucleoplasm• Chromatin• Nucleoli

Nuclear Envelope and Nucleoplasm

• Separated from cytosol by a nuclear envelope composed of two lipid bilayers

• Outer layer is continuous with Rough ER.

• Contains nuclear pores- channel through entire thickness.• Allow transport of protein

and RNA.• Area between bilayers is space

called perinuclear space.

Nucleoplasm

• The gel-like substance that fills the nucleus.

• Resembles cytosol.

DNA, RNA and Chromatin

• DNA and RNA are composed of nucleotides.• What are they?• How do they pair?• What does DNA form?

• Chromatin-fibers made up of DNA and globular proteins called histones

• Nucleosome- single strand of DNA wound around 8 histone molecules.

• During cell divison, chromatin condenses into super-coiled, x-shaped structure called chromosomes.

Nucleoli

• Not membrane bound• Where ribosomal subunits are made• Contain DNA that governs synthesis of

rRNA.

Cell Physiology

• The Cellular Environment• Body Fluids

• Composed primarily of water• Intracellular fluid- fluid found inside

cell. • Extracellular fluid- fluid outside cell.• Interstitial fluid- fluid contained within

the tissue, except for blood found within lymph and blood vessels.

Ions, Electrolytes, and pH

• What are ions?• Cations• Anions• Electrolytes

• In sick or injured animals, electrolyte concentrations and pH of intracellular and extracellular fluid can become abnormally high or low

Membrane Processes: Excretion and Absorption

• In order to maintain homeostasis cell must select what it needs from extracellular fluid and bring it into intracellular environment.

• Must excrete waste products or transport resources needed in other parts of the body to the extracellular compartment.

• Processes may be passive (do not require ATP) or active (do use ATP).

Passive Transport Processes

• Remember: No Energy Required!• 4 Passive Processes:

• Diffusion• Facilitated Diffusion• Osmosis• Filtration

Diffusion

• Kinetic movement of molecules from higher to lower concentration via concentration gradient- the difference between the concentration of one area and the concentration of another.

• Will continue until the molecule is evenly dispersed throughout the solution

• Determining factors for Diffusion thru a membrane:

1. Molecular size – small can move through

2. Lipid solubility – lipids can pass lipid bilayer

3. Molecular charge – ions move through special channel proteins

4. Temperature – faster in hot solution

Facilitated Diffusion

• Selective carrier proteins assist in movement of molecules from higher to lower concentration; speed of diffusion is limited by saturation of carrier molecules.

• http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP11103

Osmosis

• Passive movement of water through a semipermeable membrane from dilute solution to more concentrated one.

• Opposite of diffusion as water, not solute is moving. Also requires semipermeable membrane.

Filtration

• Hydrostatic pressure (caused by the beating heart) forces liquid and small molecules through a membrane.

• Liquids pushed through a membrane when the pressure on one side is greater than that on the other side.

• Example?

• http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP11103

Tonicity Terminology

• Isotonic : Extracellular fluid has same concentration of dissolved substances as intracellular fluid

• Hypotonic: Cytoplasm (inside) of cell is more concentrated than extracellular (outside) fluid

• Hypertonic: Extracellular fluid is more concentrated than cytoplasm

Active Transport Processes• Remember: Requires Energy (ATP)!• Relies on a carrier protein with a specific binding

site• Does not require a concentration gradient• Symport system – substances are moving in the

same direction• Antiport system – substances are moved in

opposite directions• Include:

• Active Transport• Endocytosis

• Phagocytosis• Pinocytosis• Receptor mediated

• Exocytosis

Active Transport

• Active movement of molecules by specific carrier protein; molecules may move against concentration gradient.

Endocytosis

• Phagocytosis• Cells engulf solid substances

• Pinocytosis• Cells engulf liquid substances

• Receptor mediated• Specialized protein receptors bind to

ligands specific receptors.• Ligand-small molecules that bond to

larger chemical groups or molecules.

Exocytosis

• Excretion of waste products and secretion of manufactured substances.

• Packaged in secretory vesicles which fuse with cell membrane and are ejected to extracellular space.

Life Cycle of the Cell

• Two types of division of cells.• Meiosis- Reduction division

• Found in reproductive cells. End up with half of what start with.

• Mitosis- exact replication of cell.

• We will focus mainly on Mitosis for this chapter.

Mitosis

• Life cycle has been divided into two major periods:• Interphase

• When cell is growing, maturing, and differentiating.

• Cells spend majority of time in this phase.• Mitotic Phase

• When cell is actively dividing.• Composed of:

• Prophase• Metaphase• Anaphase• Telophase

Interphase

• Period between cell divisions.• Nucleus and nucleoli are visible and

chromatin is arranged loosely throughout the nucleus.

• Divided into three subphases:• Growth 1 (G1)- metabolic activity and

cell growth; time variable (min-yrs) depending on cell type

• Synthetic (S)- DNA replication• Growth 2 (G2)- very brief; synthesis of

enzymes and proteins needed for mitosis

DNA Replication

• Many cells are continually replicating to maintain body tissues, to heal wounds, or to enable growth

• DNA must be replicated before the cell can divide – a copy of DNA is made to be passed to the daughter cell

• Occurs during Interphase

DNA Replication• Process:

• Enzymes called DNA helicases pull apart the parental DNA double helix so the bases no longer form base pairs

• Next, enzymes called DNA polymerases move along each separated parental DNA strand and match each base on the strand with free nucleotides that have a complimentary base (an A is matched with a T)

• Then, DNA polymerase connects the free nucleotides together to form new DNA strands

• When replication is complete, the parental strand and the new strand wind together to form a double helix

• The lead strand, is made continuously; the second (lagging) strand is made in segments, and

• DNA ligase joins the segments• The identical DNA strands become chromatids, joined together

at the centromere to form a chromosome

Lead and Lagging Strands

Mitotic Phase- Cell Division

• Cytokinesis- division of the cytoplasm.

• Prophase• Chromatin coils and are

composed of two identical chromatids

• Spindle apparatus appears• Normal synthetic processes

cease.• Nuclear envelope disintegrates

• Metaphase• Chromosomes are lined up

in center of spindle.• Centromere of each

chromosome is attached to a spindle fiber.

• Anaphase• Centromeres split apart and each

chromatid becomes its own chromosome.

• Spindle fiber separates, and chromosomes are pulled away from each other.

• Cytoplasm constricts along metaphase plate.

• Telophase• Final stage of mitosis• When chromosomal movement stops• Chromosomes reach poles and begin

to unravel.• New nuclear envelope appears as well

nucleoli.• Cytokinesis ends telophase.• New daughter cells enter interphase.

Control of Cell Division

• Some cells divide rapidly others not so fast.• Examples of each

• Normal cells stop dividing when they come into contact with surrounding cells. • Called Contact inhibition

• Division can be controlled once numbers reach a certain point.

• Proteins can also allow cells to enter mitotic phase

Protein Synthesis

• Protein synthesis is essential for life.• Begins in nucleus• tRNA transcribes DNA information

• Transcription-Genetic information in DNA is copied onto messenger RNA (mRNA)

• Codon- series of 3 RNA nucleotides.• mRNA sends information to cytoplasm

• Translation- Ribosomes bind to mRNA strand (rRNA).

• New protein building as codes are translated from nucleotides to amino acids

Genetic Mutations

• A genetic error.• Mutations may be so severe that cell dies, but may

also cause no issues whatsoever.• Some can be repaired by repair enzymes.• May occur spontaneously or due to mutagens.

• Viruses• Ionizing radiation• Certain chemicals

• What is cancer?• What is chemotherapy?

Cell Differentiation and Development

• Differentiation- The progressive acquisition of individual characteristics by cells to enable them to perform different functions.

• Differentiation is important as it keeps cells focused on a particular function.

• http://www.youtube.com/watch?v=dA5RfoGiupM

• http://www.youtube.com/watch?v=y8gZCTjAbVs&feature=related