Chapter 4-5: Cell Structures and Membrane

Function

How do we study cells?● Light microscope

○ uses light to pass through a live or dead specimen to form an image

● Transmission electron microscope (TEM)○ study the interior of cell○ 2D image

● Scanning electron microscope (SEM)○ study the surface of cells○ 3D image

● Electron microscope○ electrons pass through

specimen○ 100,000x magnification○ Only dead specimen○ 2 types

Other Methods1. Cell fractionation

○ uses centrifuge to spin samples at ultra speeds and separate liquid into different densities

○ Nucleus heaviest, followed by mitochondria/chloroplast2. Freeze fracture

○ Makes a cast of the membrane3. Tissue culture

○ grows specific cells in lab (in vitro)

Cell Theory1. All organisms are composed of

cells

2. Cells are the basic units of structure and function in organisms

3. Cells come only from preexisting cells (self-reproducing)

Why are cells so small?

Why do single-celled organisms not get bigger?

Surface Area-to-Volume Ratio (SA:VOL) ● Why are cells so small?

○ Needs large surface area to take in nutrients and remove waste

○ As cells increase in size its volume increases faster than its surface area

● This tradeoff is examined in SA:VOL○ smaller objects have larger SA:VOL

● Why is a huge single-celled creature not possible?○ Cannot move material in and out of

cell fast enough to support life

Limits to cell size● Metabolic requirements set upper limit

○ in large cell, cannot move material in and out of cell fast enough to support life

Cell Characteristics● ALL CELLS:

○ Surrounded by a plasma membrane

○ Have cytosol■ cytoplasm= cytosol+organelles

○ Contain chromosomes with have genes in the form of DNA

○ Have ribosomes■ organelles that make proteins

Types of Cells

Prokaryotic cell● DNA in nucleoid

region, without a membrane separating it from rest of cell

● Cell wall present in all (type differs)

Eukaryotic cell● chromosomes in

nucleus (membrane- enclosed nucleus)

● Cells walls present in plants only

● More complex● Membrane bound

orgaenelles present

Prokaryotic Cells● Lack membrane-enclosed nucleus

● Cellular envelope composed of plasma membrane, cell wall, and slime layer (capsule)

● Nucleoid: single, coiled chromosome● Plasmid: round extrachromosomal pieces

● One of the most abundant life-forms on earth

● ex. Bacteria

Why have organelles?● Specialized structures = specialized

functions

● Containers○ partition cell into compartments○ create different local environments○ allow for distinct and incompatible

functions

● Membranes are sites for chemical reactions○ unique combination of lipids and

proteins○ embedded enzymes and reaction

centers

FUNCTION DICTATES FORM

● All cells do not look alike

● Have similar organelles in common○ But may have more or

less depending on cell’s needs

What jobs do cell have to do?

1. Make proteinsa. proteins control every cell function

2. Make energya. For daily lifeb. For growth

3. Make more cellsa. Growth, repair, and renewal

1) Make Proteins● Organelles involved:

○ Nucleus○ Ribosomes○ Endoplasmic reticulum○ Golgi apparatus○ Vesicles

nucleus

The Nucleus● Contains genetic library

○ Cell’s DNA packed into chromatin

○ transcribes mRNA from DNA instructions

● Enclosed by nuclear envelope○ double membrane of

lipid bilayer

● Contains nucleolus○ packages ribosomal

subunits

Ribosomes● Site for protein synthesis

○ construction workers connecting one amino acid at a time to build a protein

● Free ribosomes○ suspended in cytosol○ synthesize proteins that function in

cytosol

● Bound ribosomes○ attached to endoplasmic reticulum○ synthesize proteins for export or for

membranes

Rough ER Function● Continuous with the side of the

nuclear envelope● Manufactures proteins and

enzymes that will be export for secretion

● Finalizes protein formation and prepare for export out of cell (protein folding)○ folds protein into

conformation○ Form glycoproteins

■ protein covalently bonded to carbohydrate

● Which cells have a lot of rough ER?

Golgi Apparatus● Distinct polarity: two poles cis face

(receives) and trans face (exports)● Function

○ finishes, sorts, tags & ships cell products■ like “UPS shipping department”

○ ships products in vesicles■ membrane sacs■ “UPS trucks”

Which cells have a lot of Golgi?

Put it all together

Smooth ER Function● Membrane production● Many metabolic processes:

○ synthesis■ synthesize lipids■ oils, phospholipids, steroids & sex

hormones○ hydrolysis

■ hydrolyzes glycogen into glucose● in liver

○ store calcium ions for muscle contraction

○ detoxify drugs & poisons■ in liver■ ex. alcohol

Lysosomes● Membrane-enclosed bag of hydrolytic

enzyme (pH of 5)● Function

○ little “stomach” of the cell■ digests macromolecules

(phagocytosis)○ “clean up crew” of the cell

■ cleans up broken down organelles (autophagy)

○ “auto destruction” of the cell (apoptosis)■ lysosomes break open and kill cell

● Ex. tail of tadpoles● Ex. webbing between your toes

Vacuoles ● Membrane-enclosed larger vesicle● Function

○ Storage/ Moving■ Food vacuoles

● forms during phagocytosis, fuse with lysosomes

■ Contractile vacuoles● pump excess H20 out of cell

■ Central vacuole

● contain sap, provide support

Endomembrane System

2) Making Energy● Cells must convert incoming energy into forms they can use:

○ Chloroplast:use solar energy to produce ATP and glucose■ glucose= stored energy■ ATP= active energy

○ Mitochondria: Break down glucose to produce ATP

Similarities in Energy Cells● Mitochondria and chloroplast are different (not a part

of the endomembrane system)

● Both chloroplast and mitochondria:○ Transform energy

■ generate ATP○ Have a double membrane○ Semi-autonomous organelles

■ move, change shape (grow), and divide (reproduce)

○ Internal ribosomes○ Own circular chromosomes

■ directs synthesis of proteins produced by internal ribosomes

Endosymbiotic Theory● Mitochondria and chloroplast were

once free living bacteria○ arose when an eukaryotic cell

engulfed independent eukaryotes● Endosymbiont= cells that live within

another cell (host○ partnership○ evolutionary advantage for both

■ one supplies energy■ the other protection and raw

materials● Both organelles have double

membranes and contain own genetic material separate from the nucleus

Mitochondria● Function

○ cellular respiration○ generate ATP

■ breakdown of sugars, fats & other fuels in the presence of oxygen

■ break down larger molecules into smaller to generate energy = catabolism

■ generate energy in presence of O2 = aerobic respiration

● Number of mitochondria is correlated with aerobic metabolic activity

Chloroplast● Chloroplasts are plant organelles

○ class of plant structures = plastids■ amyloplasts

● store starch in roots & tubers■ chromoplasts

● store pigments for fruits & flowers

■ chloroplasts● store chlorophyll & function

in photosynthesis● in leaves, other green

structures of plants & in eukaryotic algae

Chloroplast● Structure

○ Thylakoid= flattened sacs that stack to make a granum (grana plural)■ houses chlorophyll ■ convert light into energy

○ Stroma= fluid outside of grana● Function

○ photosynthesis○ generate ATP & synthesize sugars

■ transform solar energy into chemical energy

■ produce sugars from CO2 & H2O

Cytoskeleton● Network of fibers in the cytoplasma that

provide framework for support, movement, and regulation

● Three types of fibers○ Microtubules

■ cellular support○ Centrosomes and centrioles

■ organize microtubules during cell division

○ Cilia and flagella■ locomotor organelles

Animal vs Plant Cells● Plants have:

○ Cell wall○ Chloroplast and mitochondria○ Central vacuole

■ 90% of volume filled with sap