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Cell structure and function

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The Cell Cells:

structural and functional units of all living organisms.

building blocks of the human body. adult human body contains ~ 75 trillion

cells. Each cell type performs specific

functions. ~200 cell types in humans

subcategories of most

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Common Characteristics of Cells Perform the general functions necessary

to sustain life: Obtain nutrients and other materials from

its surrounding fluids. Fuel molecules, O2, building blocks, minerals,etc

Dispose of wastes products Urea (from nitrogen), CO2, metabolic waste

Maintain shape and integrity Size and shape are related to function

Cell division: Mitosis: growth and repair Meiosis: gamete formation

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Study of Cells Cytology: study of cells Microscopic anatomy

Individual cells observable by light microscopy

Subcellular structures observable by electron microscopy.

TEM SEM

Unit of measure: micrometer (um) RBC: 7-8um

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Cells Parts of a cell

Cell Membrane (or plasma membrane) Cytoplasm

Cytosol Organelles

Membranous Organelles Non-membranous Organelles

Inclusions Nucleus

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Plasma (Cell) Membrane

the outer, limiting barrier

separates the internal contents of the cell from external materials.

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Cytoplasm general term for all cellular

contents located between the plasma membrane and the nucleus.

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Nucleus “control center” of the cell controls protein synthesis

directs the functional and structural characteristics of the cell.

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Plasma membrane: composition Lipids

Phospholipids Head: hydrophilic Tail: hydrophobic Form lipid bilayer

Cholesterol Glycolipids

Carbohydrate component Part of glycocalyx

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Plasma membrane: composition

Protein Integral membrane proteins Peripheral membrane proteins Some serve as enzymes, ion channels

or receptors Glycoproteins

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Plasma membrane: functions Selectively permeable barrier

Nutrient in Waste out

Communication Intercellular connections Physical barrier

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Transport Mechanisms Passive Transport Active Transport Bulk Transport Solution= solvent (H2O)+ solute

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Passive Transport Movement of substances along a

concentration gradient [Hi] to [Low]

ATP is not required Types:

Simple Diffusion: solutes Facilitated Diffusion: solutes Bulk Filtration: solution Osmosis: solvent

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Facilitated Diffusion Requires the participation of

specific transport proteins that help specific substances or molecules move across the plasma membrane.

“Carrier-mediated”

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Bulk Filtration Involves the diffusion of both

solvents and solutes together across the selectively permeable membrane.

Pressure gradients

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Osmosis Involves the diffusion of a solvent

(H2O), across a selectively permeable membrane.

Can cause a volume change

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Active Transport Movement of a substance across a plasma

membrane against a concentration gradient. Materials must be moved from an area of low

concentration to an area of high concentration. requires cellular energy in the form of ATP

(adenosine triphosphate) uses transport proteins (carrier-mediated) ATP is continually synthesized by

mitochondria

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Ion Pumps Active transport processes that

move ions across the membrane are called ion pumps. ion pumps allow a cell to maintain its

internal concentrations of small molecules or ions

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Bulk Transport - Exocytosis Used by cells that secrete Usually movement of large

molecules Movement out of the cell.

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Bulk Transport - Endocytosis process by which the cell acquires materials

from the extracellular fluid: (3 Forms) Phagocytosis:

Cell forms pseudopodia engulfs a particle internalize it into a vacuole

Pinocytosis: incorporation of droplets of extracellular fluid (solution) Taken into the cell in small vesicles

Receptor-mediated endocytosis: receptors in the cell membrane Bind with specific molecules Invagination forms around them to create a

cytoplasmic vesicle

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Cytoplasm: cytosol Matrix; intracellular material Different in different cell Mostly water

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Cytoplasm: Organelles Complex, organized structures Have unique, characteristic

shapes. Each type performs a different

function for the cell. Are essential for normal cellular

structure and activities.

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Membranous Organelles Include:

Endoplasmic Reticulum Rough Endoplasmic Reticulum (RER)

Ribosomes Make protein for export Peroxisomes made here

Smooth Endoplamic Reticulum (SER) Lipids and carbohydrates Detoxification

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Membranous Organelles Peroxisomes

Vesicles formed from RER Use oxygen to detoxify Mediated by specific enzymes Most abundant in liver

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Membranous Organelles Golgi Apparatus

Modifies, stores and sorts material from RER

Receiving region (cis-face) Shipping region (trans-face)

Produces Lysosomes Autophagy: removal of old organelles Autolysis: destruction of the cell

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Mitochondria Mitochondria are organelles with a

double membrane. Produce large amounts of ATP. Are called the “powerhouses” of

the cell.

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Non-Membranous Organelles Not made of a membrane. Usually made of protein Include:

Ribosomes: free and fixed Cytoskeleton

Microfilaments Intermediate fibers microtubules

Centrosome centrioles

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Ribosomes Small, dense granules

Protein RNA

Site of protein synthesis. Each ribosome has a small and a

large subunit. small subunit is about one-half the

size of the large subunit.

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The Cytoskeleton Made of filamentous proteins Helps give the cell its shape Coordinates cellular movements. Three categories:

microfilaments intermediate filaments microtubules

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Non-membranous Organelles Centrioles and the centrosome

Centrosome Area close to the nucleus Organization site for microtubules

Centrioles (exist as a pair) In the centrosome Perpendicular to each other 9 sets of microtubule triplets Important in cell division (spindle)

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Microvilli, Cilia and Flagella Appendages extending from the surface of

some cells. Microvilli:

short, cytoplasmic extensions For absorption

Cilia: usually occur in large numbers work together to move materials or fluids along the

surface of a cell. Flagella:

longer than cilia, and usually occur as single appendages.

Move the cell

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The Nucleus Control center of cellular activities. Usually, it is the largest structure

within the cell Appears as a single spherical or

oval structure.

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The Nucleus Enclosed by a double membrane

called the nuclear envelope. The nuclear envelope:

controls the entry and exit of materials between the nucleus and the cytoplasm.

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Nucleolus The cell nucleus may contain one

or more nucleoli. Nucleoli:

are responsible for making the small and the large subunits of ribosomes.

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Chromatin and DNA DNA is the genetic material housed

within the nucleus. DNA is a polymer of nucleotides

(sugar, phosphate, nitrogen base) Is a double helix. Chromatin:

Strands of DNA and histone proteins Euchromatin: uncoiled; active Heterochromatin: coiled. inactive

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Insert Figure 2.18

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Chromosome The chromosome is the most

organized level of genetic material. Each chromosome contains a

single, long molecule of DNA and associated proteins.

Chromosomes become visible only when the cell is dividing.

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The Cell Cycle The life cycle of the cell is called

the cell cycle. New cells must be made

continuously in order for an organism to grow and replace its damaged cells.

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Mitosis and Meiosis There are two types of cell

division. Mitosis: is the cell division process

that takes place in somatic cells. Meiosis: is the cell division process

that takes place in gonads to produce gametes.

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Mitosis Interphase Prophase Metaphase Anaphase Telophase Cytokinesis

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The Stages of Mitosis Prophase – the first and longest stage

of mitosis Early prophase – chromatin threads

condense into chromosomes Chromosomes are made up of two threads

called chromatids Chromatids are held together by the

centromere Centriole pairs separate from one another The mitotic spindle forms

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The Stages of Mitosis

Prophase (continued) Late prophase – centrioles continue

moving away from each other Nuclear membrane fragments

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Early Prophase and Late Prophase

Figure 2.21

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The Stages of Mitosis

Metaphase – the second stage of mitosis Chromosomes cluster at the middle of the cell

Centromeres are aligned along the equator

Anaphase – the third and shortest stage of mitosis Centromeres of chromosomes split

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Metaphase and Anaphase

Figure 2.21

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The Stages of Mitosis Telophase – begins as chromosomal

movement stops Chromosomes at opposite poles of the cell

uncoil Resume their thread-like extended-

chromatin form A new nuclear membrane forms

Cytokinesis – completes the division of the cell into two daughter cells

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Telephase and Cytokinesis

Figure 2.21

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Tumor Normal tissue development

exhibits a balance between cell division and cell death.

If this balance is upset and cells multiply faster than they die, abnormal growth results in a new cell mass that is called a neoplasm, or tumor.

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Cancer Benign neoplasms usually grow slowly and are

confined within a connective tissue capsule. Cells within these tumors dedifferentiate—that

is, they revert to a less specialized state, and cause an increase in their own vascular supply to support their growth.

These tumors are usually not lethal, but they have the potential to become life-threatening if they compress brain tissue, nerves, blood vessels, or airways.

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Cancer Cancer is the general term used to

describe a group of diseases characterized by various types of malignant neoplasms. unencapsulated contain cells that dedifferentiate increase their vascular supply grow rapidly spread easily to other organs by way of the

blood or lymph (metastasis)

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Cancer Cancer cells lose control of their

cell cycle. they divide too frequently and grow

out of control cancer cells lose contact inhibition

they overgrow one another and lack the ability to stop growing and dividing when they crowd other cells

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Cancer Cells

Exhibit dedifferentiation and revert to an earlier, less specialized developmental state.

Produce chemicals that cause local blood vessel formation resulting in increased blood vessels in the developing tumor (angiogenesis).

Have the ability to squeeze into any space (invasiveness) permitting them to leave their place of origin and travel elsewhere in the body.

Acquire the ability to metastasize—that is, spread to other organs in the body.