Chapter 3 Cellular Organization

8/13/2019 Chapter 3 Cellular Organization

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The Cellular Level of

Organization

Chapter 3



Ch 3 Outline

Plasma membrane functions

Cellular organelles- functions

Nucleus/DNA

Diffusion/osmosis

Transport mechanisms

Transmembrane potential

Cell life cycle/regulation

Cancer

Cellular differentiation



Cell Theory

Cells are the building blocks of all life

All cells come from the division of preexisting

cells

Cells are the smallest units that perform all vital

physiological functions

Each cell maintains homeostasis at the cellular

level



An Introduction to Cells

Sex cells (germ cells)- reproductive cells

Male sperm

Female oocyte (egg)

Somatic cells (soma = body)

All body cells except sex cells



An Introduction to Cells

All cells are surrounded by a extracellular fluid(interstitial fluid)

Plasma membrane (cell membrane) separates

cytoplasm from the extracellular fluid

Cytoplasm- cell contents

Cytosol- liquid within cell

Organelles- intracellular structures



Anatomy of a Model Cell



Plasma Membrane

Functions of the Plasma Membrane Phys ical iso lat ion - barrier

Maintain homeostasis within cell

Regu lates exchange with environment

Ions and nutrients enter

Wastes eliminated and cellular products released

Monitors the environment

Extracellular fluid composition- pH, composition, concentration

Chemical signals- activation/deactivation

Structural suppo rt

Anchors cells and tissues



Plasma Membrane

Double layer of phospholipid molecules Hydrophilic heads- toward watery environment,

both sides

Hydrophobic fatty-acid tails- inside membrane Barrier to ions and water —soluble compounds

Polar

Nonpolar

Polar

Nonpolar

Polar



Plasma Membrane- Membrane Proteins

Integral proteins- within the membrane

Peripheral proteins- bound to inner or

outer surface of the membrane



Membrane Proteins

Anchoring proteins (stabilizers)- attach to inside oroutside structures

Recognition proteins (identifiers)- label cells asnormal or abnormal

Enzymes- catalyze reactions

Receptor proteins- bind and respond to ligands(ions, hormones)

Carrier proteins- transport specific solutes throughmembrane

Channels- regulate water flow & solutes through

membrane



Membrane Carbohydrates

Proteoglycans, glycoproteins, glycolipids Extend outside cell membrane

Form sticky ―sugar coat‖ -glycocalyx

Functions of the glycocalyx

Lubrication & protection

Anchoring & locomotion Specificity in binding (receptors)

Recognition (immune response)



Plasma Membrane



Organelles and the Cytoplasm

All materials inside cell & outside nucleus(thick syrupy consistency, lots of proteins)

Cytosol (fluid)

Dissolved materials: – nutrients, ions, proteins, and waste products

High potassium/low sodium

High protein

High carbohydrate/low amino acid and fat

Organelles

Structures with specific functions



Organelles

Nonmembranous organelles- no membrane

Direct contact with cytosol

Includes cytoskeleton, microvilli, centrioles, cilia,

ribosomes, proteasomes

Membranous organelles- covered with plasma

membrane

Isolated from cytosol

Includes endoplasmic reticulum (ER), the Golgi

apparatus, lysosomes, peroxisomes, mitochondria



Cytoskeleton

Structural

proteins for shape

and strength

Microfilaments

Intermediate

filaments

Microtubules



Cytoskeleton- Microfilaments

Microfilaments- thin filaments composed ofthe protein actin

Common in periphery of cell

Functions:

Anchor cytoskeleton to plasma membrane

Determine consistency of cytoplasm

Pair with thick filaments of myosin for movement

in muscle



Cytoskeleton- Intermediate Filaments

Intermediate filaments- mid-sized betweenmicrofilaments and thick filaments

Most durable (collagen)

Functions:

Strengthen cell and maintain shape Stabilize organelles

Stabilize cell position with respect to surrounding cells



Cytoskeleton- Microtubules

Microtubules- large, hollow tubes of tubulin protein

Extend outward into periphery from centrosome

Form primary components of cytoskeleton Functions:

Strengthen cell and anchor organelles

Change cell shape

Move vesicles within cell (kinesin and dynein)

Form spindle apparatus

Form structural components of cilia, centrioles



Microtubules



Microvilli

-Increase surface area forabsorption

-Attach to cytoskeleton

Actin filaments



Centrioles

Centrioles in the Centrosome:

-Form spindle apparatus during cell

division

-Centrosome: cytoplasm surrounding

centriole



Cilia

Cilia- small hair-like extensions

Cilia move fluids across the cell surface

Respiratory tract, reproductive tract



Ribosomes

Build polypeptides in protein synthesis Free ribosomes in cytoplasm- manufacture

proteins for cell

Fixed ribosomes attached to ER- manufactureproteins for secretion



Proteasomes

Contain enzymes (proteases) Disassemble damaged proteins for

recycling



Membranous Organelles

Five types of membranous organelles

Endoplasmic reticulum (ER)

Golgi apparatus

Lysosomes

Peroxisomes

Mitochondria




Network of intracellular membranes connected

to nuclear envelop

Cisternae- storage chambers within membranes




Smooth ER- no ribosomes

Rough ER- bound ribosomes

Functions:

Synthesis of proteins, carbohydrates, and lipids

Storage of synthesized molecules and materials

Transport of materials within the ER

Detoxification of drugs or toxins



Smooth ER

No ribosomes attached

Synthesizes lipids and carbohydrates:

Phospholipids and cholesterol (membranes)

Steroid hormones (reproductive system)

Glycerides (storage in liver and fat cells) Glycogen (storage in muscles)



Rough ER

Surface covered with ribosomes:

Active in protein and glycoprotein synthesis

Folds polypeptides protein structures

Encloses products in transport vesicles



Rough Endoplasmic Reticulum



Golgi Apparatus

Transport vesicles carry proteins to be excreted from

cell from ER to golgi

Vesicles enter forming face & exit maturing face

Functions:

Modifies, packages secretions Renews, modifies plasma membrane

Packages special

enzymes within vesicles for

use in cytosol

cis

trans



Functions of the Golgi Apparatus



Golgi Apparatus

Secretory vesicles: modify

& package products for

exocytosis, secretedproducts

Membrane renewal

vesicles: add or remove

membrane components,

fuse to plasma membrane



Lysosomes

Powerful enzyme-containing vesicles: lyso- = dissolve, soma = body

Breakdown, recycle large molecules & organelles

Primary lysosome: formed by Golgi apparatus,

inactive enzymes

Secondary lysosome: lysosome fused with

damaged organelle

Digestive enzymes activated

Toxic chemicals isolated



Lysosomes

Functions

Clean up inside cells

Break down large molecules

Attack bacteria

Recycle damaged organelles

Eject wastes by exocytosis

Autolysis: Auto- = self, lysis = break

Self-destruction of damaged cells:

– Lysosome membranes break down – Digestive enzymes released

– Cell decomposes

– Cellular materials recycle



Lysosome Functions



Peroxisomes

Produced from pre-existing peroxisomes, notgolgi apparatus like lysosomes

Enzymes produced by free ribosomes

Functions:

Break down fatty acids, organic compounds

Produce hydrogen peroxide (H2O2)

H2O2 is broken down into water and oxygen

Large number in liver- metabolically active



Mitochondria

Smooth outer & inner

membrane withnumerous folds-cristae

Matrix- fluid around cristae

Take chemical energy

from food (glucose):produces ATP



.



Mitochondria

Aerobic metabolism- cellular respiration Use oxygen to break down food & produce ATP

Glycolysis: glucose to pyruvic acid (in cytosol) Krebs Cycle: pyruvic acid to CO2 (in matrix)

Generates protons for ETC

Electron transport chain: oxidative phosphorylation,

generates ATP (inner mitochondrial membrane)

Role of Mitochondria in Energy



Role of Mitochondria in EnergyProduction



Nucleus

Largest organelle- cell’s control center

Nuclear envelope- double membrane around the nucleus

Perinuclear space- between 2 layers of the nuclear

envelope

Nuclear pores- communication passages



Contents of Nucleus

DNA- all information to build and run organisms

Nucleoplasm- fluid containing ions, enzymes,

nucleotides, and some RNA

Nuclear matrix- support filaments

Nucleoli- synthesize rRNA and ribosomal subunits

Nucleosomes- DNA coiled around histones

Chromatin- loosely coiled DNA (cells not dividing)

Chromosomes- tightly coiled DNA (cells dividing)



Nucleus



Organization

of DNA

within theNucleus

I f ti St i th N l



Information Storage in the Nucleus

DNA- instructions for every protein in the body

Gene- DNA instructions for one protein

Genetic code- chemical language of DNA

instructions:

Sequence of bases (A, T, C, G)

Triplet code: 3 bases = 1 amino acid





P t i S th i



Protein Synthesis

Role of Gene Activation in Protein Synthesis

Nucleus contains chromosomes

Chromosomes contain DNA

DNA stores genetic instructions for proteins

Proteins determine cell structure and function

P t i S th i



Protein Synthesis

Transcription Copies instructions from DNA to mRNA (in nucleus)

Translation

Ribosome reads code from mRNA (in cytoplasm)

Assembles amino acids into polypeptide chain

Processing By RER and Golgi apparatus produce protein

T i ti f RNA



Transcription of mRNA

A gene is transcribed to mRNA in threesteps

Gene activation

DNA to mRNA

RNA processing

T i ti f RNA




Step 1: Gene activation Uncoils DNA, removes

histones

Start (promoter ) & stop

codes on DNA marklocation of gene:

Coding strand is code for

protein

Template strand used by

RNA polymerase molecule

T i ti f RNA




Step 2: DNA to mRNA

Enzyme RNA polymerase

transcribes DNA:

Binds to promoter Reads DNA code for gene

Binds nucleotides, forming

messenger RNA (mRNA)

mRNA duplicates DNA coding

strand, uracil replaces thymine

T i ti f RNA




Step 3: RNA processing

At stop signal, mRNA detaches

from DNA molecule:

Code is edited- RNA processing Introns removed (non-coding)

Exons spliced together

Codon (3 nucleotides)

represents 1 amino acid

mRNA Transcription



mRNA Transcription



Protein Synthesis



Protein Synthesis

Translation

tRNA anticodon binds to mRNA codon

1 mRNA codon translates to 1 amino acid

Enzymes join amino acids with peptide bonds

Polypeptide chain has specific sequence of aminoacids

At stop codon, components separate

Process of Translation












Protein Synthesis



Protein Synthesis

Nucleus Controls Cell Structure



& Function

Direct control through synthesis of

Structural proteins (cytoskeleton, receptors)

Secretions

Alter internal structure of cell, sensitivity to

substances in environment, secretory functions

Indirect control over metabolism through

enzymes

Membrane Transport



Membrane Transport

Plasma membrane- barrier

Nutrients must get in

Products and wastes must get out

Permeability determines what moves in and outof a cell

Membrane that

Lets nothing in or out- impermeable Lets anything pass- freely permeable

Restricts movement- selectively permeable

Membrane Transport



Membrane Transport

Plasma membrane- selectively permeable Allows some materials to move freely

Restricts other materials

Selective permeability restricts materials based

on

Size

Electrical charge

Molecular shape

Lipid solubility



Membrane Transport Diffusion



Membrane Transport- Diffusion

All molecules are constantly in motion Molecules in solution move randomly

Random motion causes mixing

Concentration- amount of solute in a solvent

Concentration gradient- more solute in one

part of a solvent than another Diffusion is a function of the concentration gradient

Diffusion



Diffusion

Molecules mix randomly

Solute spreads through solvent

Eliminates concentration gradient

Solutes move down a concentration gradient

Factors Affecting Diffusion



Factors Affecting Diffusion

Distance the particle has to move

Molecule size- smaller is faster

Temperature- more heat, faster motion

Gradient size- difference between high & low

concentrations

Electrical forces- opposites attract, like

charges repel

Diffusion Across Plasma Membranes




Can be simple or channel mediated

Simple diffusion: through plasma membrane

Lipid-soluble compounds- alcohols, fatty acids,

steroids

Dissolved gases- oxygen, carbon dioxide

Transmembrane proteins: pass through channels

Water-soluble compounds

Ions- have a charge





Factors in channel-mediated diffusion

Passage depends on:

Size

Charge

Interaction with the channel

Diffusion Across Plasma Membrane



Diffusion Across Plasma Membrane

Osmosis: A Special Case of Diffusion



Osmosis: A Special Case of Diffusion

Osmosis- the diffusion of water across cell

membrane

More solute molecules, lower concentration of

water molecules

Membrane must be freely permeable to water,selectively permeable to solutes

Water molecules diffuse across membrane

toward solution with more solutes Volume increases on the side with more solutes

Osmosis



Osmosis

Osmosis



Osmosis

Osmotic Pressure Force of a

concentration

gradient of water

Equals the force

(hydrostatic pressure)

needed to blockosmosis

Osmolarity and Tonicity




The osmotic effect of a solute on a cell:

Two fluids may have equal osmolarity, but

different tonicity

Isotonic (iso- = same, tonos = tension)

A solution that does not cause osmotic flow ofwater in or out of a cell

Hypotonic (hypo- = below)

Has less solutes & loses water through osmosis

Hypertonic (hyper- = above)

Has more solutes and gains water by osmosis





A cell in a hypotonic solution: Gains water

Ruptures (hemolysis of red blood cells)

A cell in a hypertonic solution:

Loses water

Shrinks (crenation of red blood cells)

Osmotic Flow across a



Plasma Membrane

Carrier-Mediated Transport



Carrier Mediated Transport

Carrier-mediated transport of ions & organic

substrates

Facilitated diffusion (passive)

Active transport

Characteristics: Specificity:

One transport protein, one set of substrates

Saturation limits: Rate depends on transport proteins, not substrate

Regulation:

Cofactors such as hormones





Cotransport (symport)- two substances move in

the same direction at the same time

Countertransport (antiport)- one substance

moves in while another moves out





Facilitated diffusion- passive

Carrier proteins transport molecules too large

to fit through channel proteins (glucose, amino

acids):

Molecule binds to receptor site on carrier protein

Protein changes shape, molecules pass through

Receptor site is specific to certain molecules

Facilitated Diffusion



Facilitated Diffusion





Active transport Active transport proteins:

Move substrates against concentration gradient

Require energy, such as ATP

Ion pumps move ions (Na+, K+, Ca2+, Mg2+)

Exchange pump countertransports 2 ions at the

same time

Active Transport



Active Transport

Sodium-potassiumexchange pump

Active transport,

carrier mediated:

Sodium ions (Na+)

out, potassium ions

(K+) in

1 ATP moves 3 Na+

and 2 K+



Vesicular Transport



Vesicular Transport

Bulk transport- materials move into or out of cell in

vesicles

Endocytosis (endo- inside)- active transport using

ATP:

Receptor mediated

Pinocytosis

Phagocytosis

Exocytosis (exo- outside)

Granules or droplets are released from the cell



Receptor-Mediated Endocytosis



p y

Pinocytosis



y

Endosomes ―drink‖ extracellular fluid

Phagocytosis



g y

Pseudopodia

psuedo- false

pod- foot

Engulf large objects in

phagosomes

Exocytosis



y

Reverse of endocytosis



Transmembrane Potential



Interior of cell- negative, outside- positive

Unequal charge across the plasma membrane-

transmembrane potential

Resting potential ranges: –10 mV to –100 mV,

depending on cell type

Cell Life Cycle



y

Most of a cell’s

life is spent in

nondividing state-interphase

Cellular Life Cycle- Interphase



y p

Nondividing period G0 phase- specialized cell functions only

(neurons, muscle cells)

G1 phase- cell growth, organelle duplication,

protein synthesis

S phase- DNA replication and histone synthesis

G2 phase- finishes protein synthesis & centriole

replication

DNA Replication- S phase



p p

DNA strands unwind, DNA polymerase attaches

complementary nucleotides

Mitosis- Prophase



p

Chromosomes become visible under light microscope

Nucleoli disappear

Centriole pairs move to cell poles

Microtubules (spindle fibers) extend between centriole

pairs

Nuclear envelope disappears

Spindle fibers attach to kinetochore

Interphase Early

ProphaseLate Prophase



Prophase

Metaphase



Chromosomes align along metaphase plate

Anaphase



Microtubules pull sister chromatids apart

Telophase



Nuclear membranes reform, chromosomes uncoil

Nucleoli reappear- cell has 2 complete nuclei

Cytokinesis



y

Division of the cytoplasm

Cleavage furrow around metaphase plate

Membrane closes, producing daughter cells

Cell Differentiation



All cells carry complete DNA instructions for allbody functions- don’t look the same!

Cells differentiate- become specialized

Form distinct cell types (liver cells, fat cells, neurons) Turn off all genes not needed by that cell

All body cells, except sex cells, contain the same

46 chromosomes

Differentiation depends on which genes are

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Chapter 3 Cellular Organization