learning objectives - linn–benton community...

Learning Objectives • Know the organization of a prokaryotic cell

• Learn the organelles of a eukaryotic cell

• Consider the properties of the cell membrane (aka plasma membrane)

• How does it restrict flow of molecules across the membrane?

• Visualize the flow of endomembrane trafficking through the cell

• Overview of eukaryotic organelles

• Consider how the organelles work together

• Know the difference between diffusion and osmosis

• Identify ways that cells transport molecules across membrane barriers

• Know the difference between diffusion and osmosis

• Understand the how the properties of the plasma membrane restrict diffusion across the

membrane

• The membrane is permeable to what types of molecules?

• Become familiar with the terminology of osmosis: hypotonic, hypertonic, and isotonic

solutions

• What happens to different cell types in these solutions?

• Identify ways that cells transport molecules across membrane barriers

• What is the difference between “active transport” and “facilitated diffusion”?

• Which one requires cells to expend energy?

Cell Theory

1. All organisms are

composed of one or

more cells

2. Cells are the smallest

living things

3. Cells arise only by

division of previously

existing cells

Cell size

• Smaller cells also have a greater surface area

a cell’s surface provides the interior’s only opportunity to interact

with the environment

as cell size increases, the volume grows more rapidly than

surface area (e.g., if surface area doubles, volume quadruples)

Bacteria on the point of

a pin (!)

Microscopy Resolution: minimum distance that two points can be apart and still

be distinguished as two separated points

• the limit of resolution of the human eye is about 100

micrometers (1/10 mm)

Compound light

microscopes use sets of

magnifying lenses to resolve

structures that are separated

by more than 200

nanometers

Electron microscopes have

1000 times the resolving

power of light microscopes

and can resolve objects as

close as 0.2 nanometers

apart

Prokaryotic/Eukaryotic

There are two major types of cells

Prokaryotic

• lacks a nucleus and does not have an extensive

system of internal membranes

• all bacteria and archaea have this cell type

Eukaryotic

• has a nucleus and has internal membrane-

bounded compartments

• all organisms other than bacteria or archaea have

this cell type

Prokaryotic

Cells

Prokaryotes are the simplest cellular organisms

have a plasma membrane surrounding a cytoplasm without interior compartments

• most bacteria have additional outer layers to the plasma membrane

– cell wall comprised of carbohydrates to confer rigid structure

– capsule may surround the cell wall

Figure 4.5 Organization of a

prokaryotic cell

Prokaryotic Cell Organization

• The interior of the prokaryotic cell shows simple organization

cytoplasm is uniform with little or no internal support framework

ribosomes (sites for protein synthesis) are scattered throughout the cytoplasm

nucleoid region (an area of the cell where DNA is localized)

• not membrane-bounded, so not a true nucleus

Prokaryotic External Structures

Other structures sometimes found in prokaryotes relate to locomotion, feeding, or genetic exchange

a flagellum (plural, flagella) is a threadlike structure made of protein fibers that extends from the cell surface

• may be one or many

• aids in locomotion and feeding

pilus (plural, pili) is a short flagellum

• aids in attaching to substrates and in exchanging genetic information between cells

Eukaryotic Cells

Eukaryotic cells are larger and more complex than prokaryotic cells Also have a plasma membrane

encasing the cytoplasm • internal membranes form

compartments called organelles

• the cytoplasm is semi-fluid and contains a network of protein fibers that form a scaffold called a cytoskeleton

Eukaryotic cells have organelles

• Many organelles are immediately

conspicuous under the microscope

Nucleus

• a membrane-bounded compartment for DNA

Endomembrane system

• gives rise to the internal membranes found in the

cell

• each compartment can provide specific conditions

favoring a particular process

Figure 4.6 Structure of an animal cell

Inter-Kingdom Differences in

Eukaryotic Cells

The cells of plants, fungi, and many protists

have a cell wall beyond the plasma

membrane

All plants and many protists contain

organelles called chloroplasts

Plants contain a central vacuole

Only animal cells contain centrioles

Figure 4.7 Structure of a plant cell

Table 4.1 Be familiar with

the structures/

organelles in this

table

The Plasma Membrane

• The plasma membrane is conceptualized

by the fluid mosaic model

a sheet of lipids with embedded proteins

• the lipid layer forms the foundation of the

membrane

• the fat molecules comprising the lipid layers are

called phospholipids

What makes it a “mosaic”?

Phospholipids

• A phospholipid has a polar head and two non-polar tails

• The polar region contains a phosphate chemical group and is water-soluble (hydrophilic)

• The non-polar region is comprised of fatty acids and is water-insoluble (hydrophobic)

Figure. Phospholipid structure

Lipid bilayer

• A lipid bilayer forms spontaneously whenever a

collection of phospholipids is placed in water Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Polar

(hydrophilic) region

Nonpolar (hydrophobic) region

(a)

(b)

Chemistry of the plasma membrane

• The interior of the lipid bilayer

is completely nonpolar

no water-soluble molecules can

freely cross through it

cholesterol is also found in the

interior

• it affects the fluid nature of the

membrane

• its accumulation in the walls of

blood vessels can cause

plaques

• plaques lead to cardiovascular

disease

Do you think that cholesterol makes the plasma membrane

more or less fluid?

www.cytochemistry.net

Membrane proteins

• Another major component of the membrane is a

collection of membrane proteins

Some proteins form channels that span the

membrane

• these are called transmembrane proteins

• What must be true about the region of the protein that

spans the membrane?

Other proteins are integrated into the structure of the

membrane

• for example, cell surface proteins are attached to the outer

surface of the membrane and act as markers

Proteins are embedded within the

lipid bilayer

Polar

hydrophilic

heads

Polar

hydrophilic

heads

Nonpolar

hydrophobic

tails

Phospholipid

Cell identity

marker

Nonpolar

areas

of protein

Polar areas

of protein Phospholipids

Cholesterol

Cholesterol

Protein channel

Receptor protein

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Nucleus: The Cell’s Control

Center • The nucleus is the command

and control center of the cell

it also stores hereditary

information (in what molecule?

What theory does this relate

to?)

• The nuclear surface is

bounded by a double-

membrane called the nuclear

envelope (2 lipid bilayers!)

groups of proteins form

openings called nuclear pores

that permit proteins and RNA to

pass in and out of the nucleus

The Nucleus: DNA

• The DNA of eukaryotes is packaged into

segments and associated with protein

this complex is called a chromosome

• the proteins enable the DNA to be wound tightly

and condense during cell division

• when the cell is not dividing, the chromosomes

exist as threadlike strands called chromatin

– protein synthesis occurs when the DNA is in the

chromatin form

http://www.wehi.edu.au/education/wehitv/molecular_visualisations_of_dna/

http://www.wehi.edu.au/education/wehitv/molecular_visualisations_of_dna/

The Nucleolus

• The cell builds proteins on structures called ribosomes

ribosomes consist of ribosomal RNA (rRNA) and several

different kinds of proteins

• Ribosomes are assembled in a region of the nucleus

called the nucleolus

The Endomembrane System

• The endoplasmic reticulum (ER) is an

extensive system of internal membranes

some of the membranes form channels and

interconnections

other portions become isolated spaces

enclosed by membranes

• these spaces are known as vesicles

The Endoplasmic Reticulum (ER)

• The portion of the ER dedicated to protein

synthesis is called the rough ER

the surface of this region looks pebbly

the rough spots are due to embedded ribosomes

• The portion of the ER that aids in the

manufacture of carbohydrates and lipids is

called the smooth ER

the surface of this region looks smooth because

embedded ribosomes are scarce

Figure 4.9 The endoplasmic

reticulum (ER)

The Golgi Complex

• After synthesis in the ER, the newly-made

molecules are passed to the Golgi bodies

Golgi bodies are flattened stacks of

membranes scattered through the cytoplasm

their numbers vary depending on the cell

their function is to collect, package, and

distribute molecules manufactured in the cell

the Golgi bodies of a cell are collectively

called the Golgi complex

Figure 4.10 Golgi complex

http://molecularmovies.com/movies/berry_golgi.mov

http://molecularmovies.com/movies/berry_golgi.mov

ER-Golgi trafficking

The ER and Golgi

complex function

together as a

transport system in

the cell

Figure 4.11 How the

endomembrane system

works

https://www.youtube.com/watch?

v=rvfvRgk0MfA

https://www.youtube.com/watch?v=rvfvRgk0MfA

https://www.youtube.com/watch?v=rvfvRgk0MfA

Lysosomes

The Golgi complex also gives rise to

lysosomes

these membrane-bounded structures contain

enzymes that the cell uses to break down

macromolecules

• worn-out cell parts are broken down and their

components recycled to form new parts

• particles that the cell has ingested are also

digested

Animation: Lysosome

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Inquiry & Analysis

How Does pH Affect a Protein’s Function?

1. Which of the three pH values

represents the highest

concentration (amount present

in a given volume) of H+ ions? Is

this value more acidic or more

basic than the other two?

2. What is the percent hemoglobin

bound to O2 for each of the

three pH concentrations at

saturation? At an oxygen level

of 20 mm Hg? At 40 mm Hg? At

60 mm Hg?

3. At an oxygen level of 40 mm

Hg, would hemoglobin bind

oxygen more tightly at a pH of

7.8 or 7.0?

4. How does pH affect the release

of oxygen from hemoglobin?

Plant cell

wall

Vacuole

membrane

1.83 μm

Central

vacuole

Vacuoles

Vacuoles are membrane-

bounded storage compartments

• in plants, the central vacuole

stores water and dissolved

substances

• in some protists, the

contractile vacuole is found

near the cell surface and

accumulates excess water

from inside the cell that it then

pumps out

Organelles That Harvest Energy

• Eukaryotic cells contain energy harvesting organelles that contain their own DNA

these organelles appear to have been derived from ancient bacteria that were taken up by eukaryotic cells (endosymbiosis)

these organelles include mitochondria and chloroplasts

Mitochondria

• Mitochondria are cellular

powerhouses

• Sites for chemical

reactions called

oxidative metabolism

• The organelle is

surrounded by two

membranes

Figure 4.13(a) Mitochondria

Chloroplasts

• Chloroplasts are the sites of photosynthesis

• The organelle is also surrounded by two membranes

Figure 4.14 A chloroplast

Endosymbiosis

Both mitochondria and chloroplasts possess their own

molecule of circular DNA

• They cannot be grown free of the cell

they are totally dependent on the cells within which they occur

The theory of endosymbiosis

states that some organelles evolved from a symbiosis in which

one cell of a prokaryotic species was engulfed by and lived inside of a eukaryotic cell

the engulfed species provided their hosts with advantages because of special metabolic activities

What biological “theme” from Chapter 1 does this relate to?

Support for Theory of Endosymbiosis

In addition to the double membranes and circular DNA found in mitochondria and chloroplasts, there is a lot of other evidence supporting endosymbiotic theory

mitochondria are about the same size as modern bacteria

the cristae in mitochondria resemble folded membranes in modern bacteria

mitochondrial ribosomes are similar to modern, bacterial ribosomes in size and structure

mitochondria divide by fission, just like modern bacteria

The Cytoskeleton: Interior

Framework of the Cell

• The cytoskeleton is comprised of an internal framework of protein fibers that anchors organelles to fixed locations

supports the shape of the cell

helps organize ribosomes and enzymes needed for synthesis activities

• The cytoskeleton is dynamic and its components are continually being rearranged

Three different types of protein fibers

comprise the cytoskeleton

Intermediate filaments

• thick ropes of intertwined protein

Microtubules

• hollow tubes made up of the protein tubulin

Actin filaments (microfilaments)

• long, slender microfilaments made up of the

protein actin

Figure. The protein fibers of the cytoskeleton Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Fibrous

protein

10 nm

Intermediate filament

25 nm

+ end

Microtubule

7 nm

Actin filament Actin

subunit

Tubulin

subunit

– end

Figure 4.16 Centrioles

Centrioles are complex

structures that assemble

microtubules in animal cells and

the cells of most protists

they occur in pairs

they are found near the

nuclear envelope

they are composed of

microtubules

Motility

Cellular motion is associated with the movement of actin microfilaments and/or microtubules

some cells “crawl” by coordinating the rearrangement of actin microfilaments

some cells swim by coordinating the beating of microtubules grouped together to form flagella or cilia

Figure 4.17 Flagella and cilia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Microtubules

Plasma

membrane

Flagellum

Basal body

Microtubules (a)

(b)

© Manfred Kage/Peter Arnold/Photolibrary

Diffusion and Osmosis

• Movement of water and nutrients into a cell or elimination of wastes out of cell is essential for survival

• This movement occurs across a biological membrane in one of three ways

• diffusion

• membrane folding

• transport through membrane proteins

Diffusion

• Molecules move in a random fashion but there is a tendency to produce uniform mixtures

• The net movement of molecules from an area of higher concentration to an area of lower concentration is termed diffusion

• Molecules diffuse down a concentration gradient from higher to lower concentrations diffusion ends when equilibrium is reached

Animation: How Diffusion Works













Diffusion across the cell membrane

Only certain substances undergo diffusion across the plasma membrane—which ones? molecules like oxygen, carbon dioxide, and lipids

or

ions and polar molecules

• Water is able to diffuse freely across the plasma membrane aquaporins are selective

channels that permit water to cross

Osmosis

Water moves down its concentration

gradient into or out of a cell through

osmosis What do we mean by “down its concentration

gradient?

the movement of water is dependent on the

concentration of other substances in a

solution

the greater the amount of solutes that are

dissolved in a solution, the lesser the amount

of water molecules that are free to move

Essential Biological Process 4B: Osmosis

1 2 3

Diffusion then causes free water

molecules to move from the side where

their concentration is higher to the solute

side, where their concentration is lower.

Addition of solute molecules that cannot

cross the membrane reduces the

number of free water molecules on that

side, as they bind to the solute.

Diffusion causes water molecules to

distribute themselves equally on both

sides of a semipermeable membrane.

Water

molecules

Hypotonic Hypertonic

Urea

Isotonic

Semipermeable

membrane


Animation: How Osmosis Works













Animation: Osmosis

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Osmotic concentration

The concentration of all molecules dissolved in a solution

if the osmotic concentrations of two solutions is equal,

the solutions are each called isotonic

if two solutions have unequal osmotic concentration, the solution with the higher solute concentration is said to be hypertonic, and the solution with the lower solute concentration is said to be hypotonic

Hyper = more, Hypo = less; Tonic = solute (dissolved substance)

Osmotic pressure

Movement of water by osmosis into a cell

causes pressure called osmotic pressure

enough pressure may cause a cell to swell

and burst

osmotic pressure explains why so many cell

types are reinforced by cell walls

Figure 4.18 Osmotic pressure in

plants and animal cells

Animation: Hemolysis and

Crenation

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Bulk Passage into and out of Cells

• Bulky substances are contained within

vesicles as they are moved into and out of

a cell

endocytosis is the engulfing of substances

outside of the cell in order to form a vesicle

that is brought inside the cell

exocytosis is the discharge of substances

from vesicles at the inner surface of the cell

Endo = In, Exo = Out

4.10 Bulk Passage into and out

of Cells Forms of endocytosis

• Phagocytosis is

endocytosis of

particulate (solid)

matter

• Pinocytosis is

endocytosis of liquid

matter

Figure 4.19 Endocytosis

Figure 4.20 Exocytosis

Animation: Endocytosis and

Exocytosis

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Selective Permeability

Selective permeability allows cells to

control specifically what enters and leaves

involves using proteins in the membrane for

transporting substances across

transport can be down a concentration

gradient (i.e., diffusion) or against a

concentration gradient (i.e., active transport)

Selective

Permeability-Diffusion Selective diffusion

• proteins act as open channels for whatever is small enough to fit inside the channel

• this form of diffusion is common in ion transport

Facilitated diffusion • proteins act as carriers that can bind only

to specific molecules and transport them

• transport is limited by the availability of carriers

• when all the carriers are in use, then the transport is saturated

Animation: How Facilitated

Diffusion Works

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Active transport

Active transport utilizes protein channels that open only when energy is supplied

energy is used to pump substances against or up their concentration gradients

allows cells to maintain high or low concentration of certain molecules

• recall that diffusion always ends in equilibrium

Most of the active transport in cells is carried out by the sodium-potassium pump

The Sodium-Potassium pump

Sodium-potassium (Na+-K+) pump

uses energy, in the form of ATP, to pump

three Na+ out of the cell and to pump two K+

into the cell

nearly 1/3 of the energy expended by the

body’s cells is given over to driving these

pumps

Essential Biological Process 4D:

The Sodium-Potassium Pump

P

P

The splitting of ATP provides energy to change the shape of the

transport protein. The sodium ions are driven through the pump.

The sodium ions are released to the outside of the membrane,

and the new shape of the pump allows two potassium ions to

bind.

Release of the phosphate allows the sodium-potassium

pump’s transport protein to revert to its original form,

releasing the potassium ions on the inside of the membrane.

3 4

The sodium-potassium pump utilizes a transport protein that

binds three sodium ions and a molecule of ATP.

Na+ P

P P

A

1

Na+

K+

P P

A A D P

P

2

Na+

Na+

Na+

K+

Na+

Na+

Na+

K+

K+

K+

K+

ATP

ADP

P P

A

Na+


Animation: How the Sodium

Potassium Pump Works













Ion gradient

• The result of the Na+-K+ pump is to generate a concentration gradient with more Na+ outside of the cell than inside

• Cells exploit this gradient in key ways

for the conduction of signals along nerve cells

for the transportation of important molecules into the cell against their concentration gradient

Coupled Transport

• The cell membrane has many facilitated diffusion channels for Na+ but it is only transported if partnered with another substance this is called coupled transport

• The concentration gradient favoring the entry of Na+ into the cell is so strong that a coupled substance will be transported even if it is against the concentration gradient coupled transport is a common way for cells to

accumulate sugars and amino acids

Animation: The Sodium

Potassium Exchange Pump

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The Flow of Energy in Living

Things

• Energy is the ability to do work [ W = F • s ]

• Energy is considered to exist in two states kinetic energy

• the energy of motion

potential energy • stored energy that can be used for motion

• All the work carried out by living organisms involves the transformation of potential energy to kinetic energy

Figure 5.1 Potential and kinetic energy

(a) Potential energy

(b) Potential energy


a: © Nice One Productions/Corbis RF

(c) Kinetic energy

Question from the reading:

• Is the energy in a “high-

energy” food bar kinetic or

potential?

Solar Chemical

Energy from the sun is captured by some organisms and used to make molecules

these molecules then contain potential energy due to the arrangement of their atoms

the potential energy in molecules is a form of chemical energy that can be used to do work in cells

chemical reactions involve making and breaking bonds between atoms

Heat Energy

• Heat energy is the

most convenient form

of energy to measure

• Thermodynamics is

the study of energy or

heat changes

There are many forms of energy but all of them

can be converted to heat

The Laws of Thermodynamics

Laws of thermodynamics govern the energy changes of the universe, including those involved with any activity of an organism

• 1st Law of Thermodynamics the total amount of energy in the universe remains constant

energy can change from one state to another but it can never be created nor destroyed

during the energy conversions, some of the energy is lost as heat energy

• 2nd Law of Thermodynamics the amount of disorder, or entropy, in the universe is increasing

Figure 5.3 Entropy in action

• What process did

we experiment

with in lab 2 that

exemplifies

entropy?

• What is an

example of a

cellular

mechanism that

uses energy to

reverse entropy?

Chemical Reactions

• The starting molecules of a chemical reaction are called

the reactants or substrates

• The output molecules from the reaction are called

products

What are the substrates?

What are the products?

Where is the energy?

Is the energy kinetic or potential?

Endergonic vs. Exergonic

There are two kinds of chemical reactions

endergonic reactions have products with more energy than the

reactants

• these reactions require an input of energy

exergonic reactions have products with less energy than the

reactants

• these reactions tend to occur spontaneously

Is polysaccharide

formation endergonic

or exergonic?

Exergonic Reactions

Question:

• If exergonic reactions tend to occur

spontaneously, why haven’t they all done so?

Activation Energy

• All chemical reactions require an initial input of

energy called activation energy

the activation energy initiates a chemical reaction by

destabilizing existing chemical bonds

Catalysis .

Reactions become more

likely to happen if their

activation energy is lowered

this process is called

catalysis

catalyzed reactions proceed

much faster than non-

catalyzed reactions

Enzymes

Enzymes are the catalysts used by cells to

perform particular reactions

enzymes bind specifically to a molecule and

stress the bonds to make the reaction more

likely to proceed

the active site is the site on the enzyme that

binds to a reactant

the site on the reactant where the enzyme

binds is called the binding site

Figure 5.5 An enzyme’s shape

determines its activity

Induced fit

How Enzymes Work

• The binding of a reactant to an enzyme causes the enzyme’s shape to change slightly

this leads to an “induced fit” where the enzyme and substrate fit tightly together as a complex

the enzyme lowers the activation energy for the reaction

the enzyme is unaffected by the chemical reaction and be re-used

Essential Biological Process 5A:

How Enzymes Work

Animation: How Enzymes Work


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Animation: Enzyme Action and the

Hydrolysis of Sucrose

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Biochemical Pathways

• Catalyzed reactions

may occur together in

sequence

the product of one

reaction is the

substrate for the next

reaction until a final

product is made

the series of reactions

is called a

biochemical pathway

Figure 5.6 A biochemical pathway

Animation: A Biochemical Pathway


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Factors Affecting Enzymes

• Temperature and pH affect enzyme activity

enzymes function within an optimum temperature

range

• when temperature increases, the shape of the enzyme

changes due to denaturing of the protein chains

enzymes function within an optimal pH range

• the shape of enzymes is also affected by pH

• most human enzymes work best within a pH range of 6 - 8

– exceptions are stomach enzymes that function in acidic ranges

Figure 5.7 Enzymes are

sensitive to their environment

Why might a human

enzyme need to

function at low pH?

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