The Cell and Cellular transport

1

The CellCell theory (1838):1. All organisms are composed of one or more cells, and the life processes of

metabolism and heredity occur within these cells.2. Cells are the smallest living things, the basic units of organization of all organisms.3. Cells arise only by division of a previously existing cell.

Common to ALL types of cells…

Cell membrane(controls the movement of things in and out of the cell)

Cytoplasm or cytosol(intracellular fluid)

Ribosomes (for protein

synthesis)

Enzymes(for metabolic reactions)

ATPATP

Energy currency(to provide energy for metabolic processes)

DNA for the genetic codeRNA for transcription of the code during protein synthesis

How many types of cells?

Only ribosomes, NO other organelles. Ribosomes are different in structure to those of eukaryotes

Several specialized organelles

Unicellular organisms

bacteria

Unicellular or (most of them) multicellular organisms

Interior of the cellOnly cytoplasm

Interior of the cellComposed of Nucleus + Cytoplasm

Prokaryotic

Eukaryotic

The Cell and Cellular transport

2

Why cells are not bigger?Practical reasons! communication

the different regions of a cell need to communicate with one another for the cell as a whole to function effectively

What is the size of a cell?Most of them smaller than 50µm (0.0020 inches)

Ratio: Surface AreaVolume

Increases with 12

Increases with 13

10cm1cm

4,189 cm34.189 cm3Volume (4/3)πr3

1,257 cm212.57 cm2Surface Area (4πr2)

Cell radius (r)

1000 times more volume!

Cell surfaceresponsible for the

interaction with the environment

small cells have bigger surface area per unit of volume than large ones

control is more effective (ex: 3 vs. 0.30)

Cell membranes Extracellular side

CytoplasmCholesterol

Peripheral protein(surface)

integral protein (inside the membrane)Two layers of

phospholipids and proteins

Also cholesterol and proteins

Fluid-mosaic model

Molecules in the membrane are able to flow and move around

Interaction of molecules with its surroundings allows the membrane to maintains its forms

Phospholipids heads (hydrophilic)

FattyAcids tails

(hydrophobic)

phospholipids

The Cell and Cellular transport

3

Cellular Organelles in Animal Cells(Eukaryotic cells)

Mitochondria

nucleolus

Nucleus

Golgi apparatus

Endoplasmic reticulum (ER)

Cytoskeleton

Ribosomes

LysosomesCentriolesExclusive

of animalscells

1) “Membrane” organelles

Mithocondrion

Inner membrane

cristae•Aerobic cellular respiration• Glu+O2 CO2+H2O •Energy conversion and release (in the form of ATP)

Nuclear membrane: Protects the DNA inside the cell.

pores allow molecules to pass from one side to the other

nuclear membrane

Nucleolus: site of ribosome manufacture

Endoplasmatic reticulum (ER): folded membranes and tubes huge surface area many chemical reactions in a small place!

Rough ERRibosomes associated to the membrane proteins synthesis

Smooth ERLipids synthesis, destruction of toxic substances

Golgi Apparatus: 5 to 20 membranous and smooth sacs modification of products (ex: activation of enzymes) from the ER, packing and export to the cytoplasm or extracellular space of certain molecules

vesicles

Lysosomes: Vesicles generated in the Golgi apparatus containing hydrolytic enzymes. Are use to degrade molecules

The Cell and Cellular transport

4

2) “Protein” organelles

Ribosomes: •Two subunits composed of RNA and proteins •Responsible for proteins synthesis•Associated to the Rough ER or free in cytoplasm

Centrioles: •Arrangement of two sets of microtubules (proteins!) at right angles•Organize microtubules assembly for cell division (chromosomes attach to microtubules)

Cytoskeleton: •Microtubules, microfilaments, and intermediate filaments proteins!•Interconnect and attach to the membrane cell

Cilia and Flagella: • hairlike structures used for locomotion•Made of microtubules (two types of proteins in Eukaryotes and only one type in Prokaryotes) with a specific arrangement•Energy is needed to move microtubules and cause movement

Eukaryotic cilia and flagella

cilia

flagella

Higher concentration

Equal Concentrations (dynamic equilibrium)

Cellular transportMovement of particles across the cell membrane. allow the cell to carry out the metabolic processes needed to live

Passive: NO energy is requiredActive: Energy is used (ATP)

Higher concentration

Equal Concentrations (dynamic equilibrium)

Lowerconcentration

Diffusion:(passive) Movement of molecules down a

concentration gradient from where are in higher concentration to where are in lower concentration.

Lowerconcentration

Osmosis: (passive) Net movement of water through a selectively permeable membrane.

1) Osmosis is a special type of diffusion in which the diffusing substance can be only water2) The regions of different concentrations are separated by a membrane permeable to water but not to the solute

Isotonic Hypotonic HypertonicRed blood cell (RBC) is…

less solutes in the RBC

more solutes in the RBC

The Cell and Cellular transport

5

Carrier Proteinscontrolled methods of transporting molecules

conc

entra

tion

-

+

Facilitated diffusion(passive) movement of molecules down a concentration gradient through the membrane by combining with specific carrier proteins.

ATPADP+Pi

Active transport(active)

Movement of molecules up a concentration gradient. An input of energy (ATP) is needed to move the molecule against its concentration gradient.

Endocytosis & Exocytosis: Transport of materials into and out of the cell by

formation of vesicles of cell membrane containing the particles, food, or materials

Pinocytosis: molecules engulfed are dissolved in water liquidsPhagocytosis: solid materials, the sac is named phagosome (ex: viruses, food, bacteria, lipoproteins)

The Cell and Cellular transport

6

Special proteins that acts as catalysts in chemical reactionsbetween substances

Speed up reactions but are not used in the reactionWhy do we need to speed up

reactions using enzymes?

Ene

rgy

Ene

rgy

product

reactants

(Products have more energy than reactants)

time

Endergonic reaction

Ea

Estored

product

reactants

Exergonic reaction

(Products have less energy than reactants)

time

Ea

Ereleased

Spontaneously would take millions of years!

Do not occur spontaneously

Energy is stored in covalent bonds of nutrients we incorporate with the food

Enzymes

Extra energy required to destabilize existing chemical bonds and initiate a chemical reaction between two or more molecules

Molecules synthesis/breakdown and energy conversion require energy to initiate the breakdown of nutrients

Energy of Activation (Ea)

reactants

productEne

rgy

rele

ases

Ea No enzyme (uncatalyzed)

1. Enzymes lower the energy of activation (Ea)

Reactions occur very fast

Ea enzyme(catalyzed)

Ene

rgy

used

Summary…

2. Enzymes are substrate specificOnly speed up the reaction

of one type of molecule

3. Enzymes remain unchangedBecause they are not

used in the reaction

4. Enzymes can be reusedbillions of times

One single enzyme can convert millions of substrate molecules per second!

The Cell and Cellular transport

7

Ex: amino acid 1

Ex: amino acid 2Ex: hydrolysis

How do enzymes speed reaction rates?Three-dimensional shape of the enzyme allows it to combine with reactants, lower the Ea and accelerate the reaction

Ex: dipeptide(two amino acids)

Enzyme-substrate complex

Ex:dehydration

ACTIVE SITE:Is the part of the ENZYME where the chemical reaction takes place,

where the energy of activation is lowered by the enzyme so the reaction can happen

3) Cofactors ARE inorganic ions (zinc, iron, magnesium). Coenzymes are organic molecules

4) As in the case of some fatty acids and amino acids, some coenzymes cannot be produced by the body and need to be obtained with the diet. Cells need vitamins in order to have coenzymes.

2) Enzymes are substrate specific but coenzymes can work with several different enzymes

ions or molecules that attach to the enzyme and help to speed up the reactionCofactors & coenzymes: enzyme helpers”

1) Cofactors help removing one of the end products or bring in part of the substrate

The Cell and Cellular transport

8

What environmental factors affect the enzymes activity?

1) TemperatureOptimum (temperature range at which

the speed of product generation is maximum) is around human body normal temperature

The speed of the reaction, or the number of molecules of substrate that one enzyme can react with in a given time, decreases as temperature moves right or left of the optimum range.

At higher or lower temperatures than the optimum, Enzymes can lose theirconfiguration (be completely unfolded and only retain the primary structure) and be no longer active

DenaturationLost of the structures of a protein, only the primary structure remains

Enzyme DenaturedEnzyme(1ry structure = sequence of amino acids)

Changes in pH determine the number of H+ ions available in the enzyme environment

these H+ may interact with exposed side-chains of the polar enzyme molecule

enzyme activity changes

Is important in defining the final shape of proteinseach enzyme reaches it maximum activity level at a given pH

2) pH

DenaturationLost of the structures of a protein, only the primary structure remains