EVPP 110 Lecture

EVPP 110 Lecture
Dr. Largen - Fall 2002

Life: Cell Structure and Major Processes for Fueling Life’s Activity

Structure of the Cell

Introduction to the cell

Before microscopes (first used in 17th century), no one knew living organisms were composed on cells

All cells share fundamental features

Major features common to all cells

plasma membrane

DNA

cytoplasm

carry out metabolism

All cells share fundamental features

Major features common to all cells

plasma membrane = encloses a cell and separates its contents from its surroundings

is a phospholipid bilayer 5-10 nanometers thick
contains embedded proteins

All cells share fundamental features

Major features common to all cells

DNA – the hereditary molecule

prokaryotes

nucleoid – area near center of cell, contains circular molecule of DNA

not differentiated from the rest of the cell’s contents by membrane

eukaryotes

nucleus – double-membrane bound organelle which contains the DNA

All cells share fundamental features

Major features common to all cells

cytoplasm

semi-fluid matrix that fills the interior of the cell, exclusive of the nucleoid or nucleus

contains the chemical wealth of the cell

sugars

amino acids

proteins

contains organelles in the eukaryotes

All cells share fundamental features

Major features common to all cells

carry out metabolism

the interconversion of different forms of energy and of chemical materials

two major metabolic processes

photosynthesis
cellular respiration

All cells share fundamental features

the primary tenants of the Cell Theory

all organisms are composed of 1 or 1+cells

where processes of metabolism & heredity occur

the cell is the smallest (basic) unit of life

the smallest living thing

cells arise only by the division of a previously existing cell

life evolved spontaneously on early earth

all life on earth represents a continuous line of descent from those early cells

Introduction to the cell

Two kinds of structurally different cells have evolved over time

prokaryotic cells

Archaebacteria

Eubacteria

eukaryotic cells

Protista

Fungi

Plantae

Animalia

Introduction to the cell

Prokaryotic cell characteristics

small, avg. 1/10th size of eukaryotic cell

lacks a nucleus

DNA contained in nucleoid region which is not membrane bound

surrounded by plasma membrane

most also have bacterial cell wall

some also have a 3rd layer-the capsule

some have projections called pili (sticky)

some are propelled by a flagellum

Introduction to the cell

Eukaryotic cells

name eukaryotic, from Greek eu for "true" and karyon for kernal or "nucleus"

are fundamentally similar to each other

profoundly different from prokaryotic cells

characteristics of eukaryotic cells

in general

comparing animal and plant cell

Introduction to the cell

Eukaryotic cells

presence vs. absence of cell walls

animal cells lack cell walls

some protists lack cell walls

plants, fungi and some protists have cell walls

Introduction to the cell

Eukaryotic cells

have complex interior organization

extensive compartmentalization

many membrane-bound organelles

true, membrane-bound nucleus

complex DNA molecule

contain vesicles and vacuoles which function in storage and transport

Introduction to the cell

Eukaryotic cells

membranes partition the cytoplasm into compartments called membranous organelles

many of the chemical activities known as cellular metabolism

occur in the fluid-filled spaces within the membranous organelles

w/o internal membranes, eukaryotic cells wouldn’t have enough membrane surface area to meet metabolic needs

Introduction to the cell

Eukaryotic cells, animal vs. plant

animal cells

cell wall absent

chloroplasts absent

central vacuole absent

mitochondria present

centrioles present

lysosome present

flagella may be present

Introduction to the cell

Eukaryotic cells, plant vs. animal

plant cells

cell wall present

chloroplasts present

mitochondria present

central vacuole present

flagella absent (except in some sperm)

lysosome absent

centrioles absent

Introduction to the cell

membranous organelles

nucleus

endoplasmic reticulum

Golgi apparatus

mitochondria

lysosome

peroxisome

chloroplast

central vacuole

Introduction to the cell

non-membranous structures

centriole

flagellum

ribosome

microtubule

microfilament

cell wall

Energy converting organelles

Chloroplasts are the photosynthesizing organelles of plants and protists

internal membranes create 3 compartments

space between inner and outer membranes

space enclosed by inner membrane

space inside tubules and disks

Energy converting organelles

Chloroplasts

space between inner & outer membranes

called intermembrane space

space enclosed by inner membrane

contains thick fluid called stroma

network of tubules and hollow disks

space inside tubules and disks

disks occur in stacks, called grana

grana are the chloroplasts solar power packs

Energy converting organelles

Mitochondria

organelles that convert chemical energy from one form to another

carryout cellular respiration, in which

chemical energy of foods such as sugars

converted to chemical energy of a molecule such as ATP (adenosine triphosphate)

ATP is main energy source for cellular work

Energy converting organelles

Mitochondria

enclosed by 2 membranes, has 2 compartments

space between inner & outer membrane

intermembrane space

a fluid filled compartment

space enclosed by inner membrane

contains fluid called mitochondrial matrix

Energy converting organelles

Mitochondria

space enclosed by inner membrane

contains mitochondrial matrix

many of the chemical reactions of cellular respiration occur here

inner membrane has many folds

called cristae

increases surface area

contains enzymes that make ATP

Fueling the activities of life

two main mechanisms by which organisms obtain food for the activities of life

autotrophs (self-sustaining)

heterotrophs (not self-sustaining)

Fueling the activities of life

two main mechanisms by which organisms obtain food for the activities of life

autotrophs (self-sustaining)

plants and other photosynthetic organisms

can produce from inorganic compounds the organic molecules they need for life

Fueling the activities of life

two main mechanisms by which organisms obtain food for the activities of life

heterotrophs (not self-sustaining)

animals

must obtain the organic molecules that they need by consuming organic molecules already produced by other organisms

Fueling the activities of life

heterotrophs have two main methods of feeding

absorptive feeders

lack mouth or digestive tract
absorb nutrients through their body surface
example, tapeworms

ingestive feeders

ingest living or dead organisms (plant or animal) through a mouth

Fueling the activities of life

Ingestive feeders are divided into three groups on the basis of their food sources

omnivores

herbivores

carnivores

Fueling the activities of life

Ingestive feeders

omnivores

ingest both plants and animals
ex., humans, crows, cockroaches,

herbivores

ingest plants and algae
examples, cattle, deer, gorillas

carnivores

ingest animals
examples, lions, hawks, spiders, snakes

How organisms harvest energy from food molecules

Two major processes enable organisms to fuel the processes of life

hetertrophs

ingest their food

cellular respiration harvests the energy from the food molecules

autotrophs

manufacture their own food via photosynthesis

cellular respiration harvests the energy from the food molecules

Cellular Respiration

Introduction to Cellular Respiration

Respiration often used as synonym for breathing

respiration refers to an exchange of gases

organism obtains O₂ from its environment & releases CO₂

Cellular respiration

the aerobic harvesting of energy from food molecules by cells

Introduction to Cellular Respiration

Breathing and cellular respiration are related

organism takes in O₂ from its environment

distributes O₂ to its cells
mitochondria in cells use O₂ in cellular respiration

to harvest energy that cell uses to do work
CO₂ waste produced by cellular respiration in cells is removed to external environment

Introduction to Cellular Respiration

Harvesting energy from food molecules is a fundamental function of cellular respiration

glucose is usually used as a representative food molecule

cells may use many organic molecules in cellular respiration

summary equation for cellular respiration

C₆H₁₂O₆ + 6O₂ ® 6CO₂ + 6H₂O + ATPs

bond energy from reactants is stored in the chemical bonds of ATP

Introduction to Cellular Respiration

Efficiency of cellular respiration

glucose contains a lot of chemical energy

but each ATP molecule made by cellular respiration contains only about 1% of the amount of chemical energy present in one glucose molecule

cellular respiration is not able to harvest all the energy of glucose in a usable form

a typical cell banks about 40% of glucose’s energy in ATP molecules
most of other 60% is converted to heat

Introduction to Cellular Respiration

Efficiency of cellular respiration

comparison

glucose burned in lab converts 100% of its energy to heat and light
glucose "burned" in cell converts about 40% its energy into stored energy in ATP molecules
gasoline engine converts about 25% of the energy in gasoline into the kinetic energy of movement

Introduction to Cellular Respiration

Cellular respiration is more efficient than any other process a cell can perform without oxygen

a yeast cell in an anaerobic environment harvests only about 2% of the energy in glucose

Basic Mechanisms of Energy Release & Storage

Underlying mechanisms of energy release and harvest in the cell

energy available to a cell is contained in the specific arrangement of electrons in chemical bonds of a molecule (glucose)

cellular respiration dismantles glucose in a series of steps

taps the energy carried by electrons
that are rearranged when old bonds break and new bonds form

Basic Mechanisms of Energy Release & Storage

cellular respiration shuttles electrons through a series of energy releasing reactions

at each step, electrons start out in a molecule where they have more energy & end up in molecule where they have less energy

thus, energy is released in small amounts
cell stores some of that energy in ATP

cells transfer energy from glucose to ATP by coupling exergonic & endergonic reactions

Basic Mechanisms of Energy Release & Storage

cellular respiration shuttles electrons through a series of energy releasing reactions

movement of hydrogen atoms in chemical equation for cellular respiration can illustrate electron transfers

glucose loses hydrogen atoms as it is converted to carbon dioxide
molecular oxygen gains hydrogen atoms as it converted to water
oxygen serves as the ultimate electron acceptor in cellular respiration

Mechanisms of Energy Release & Storage

Movement of electrons from one molecule to another is an oxidation-reduction reaction (redox)

oxidation is the loss of electrons from one substance (molecule is oxidized)

reduction is the addition of electrons to another substance (molecule is reduced)

oxidation-reduction reactions always go together because an electron transfer requires both a donor and an acceptor

Mechanisms of Energy Release & Storage

Movement of electrons from one molecule to another is an oxidation-reduction reaction (redox)

glucose gives up energy as it is oxidized

enzymes remove electrons from(oxidize) glucose and transfer them to (reduce) a coenzyme

electrons are moved about by moving hydrogen atoms (along with their electrons)

Mechanisms of Energy Release & Storage

electron cascade in which electrons "fall" down an energy "hill" of electron carriers

each electron carrier is a different molecule

electrons move "downhill" because each carrier molecule has a greater affinity for electrons than its uphill neighbor

at each step, the redox reactions release energy in small amounts, useful to the cell

last molecule at the bottom of the hill is O₂

with greatest electron affinity of all the carriers

Mechanisms of Energy Release & Storage

Electron transport chains

series of electron carriers

ordered groups of molecules embedded in the membranes of a eukaryotic cell’s mitochondria

in prokaryotes, they are located in the plasma membrane

as electrons pass along chain, they lose energy

which the cell can use to make ATP

Stages of Cellular Respiration

Cellular respiration is a continuous process but it can be divided into

three main stages

1st & 2nd stages are exergonic

glycolysis

Krebs cycle

3rd stage is endergonic

electron transport chain & chemiosmosis

Stages of Cellular Respiration

Glycolysis

first stage of cellular respiration

occurs outside the mitochondria in the cytoplasm of the cell

means "splitting of sugar"

universal energy-harvesting process of life

occurs in all cells
because of its universality, it is thought to be an ancient metabolic system

starts with glucose

Stages of Cellular Respiration

Krebs cycle

2nd stage

takes place in the mitochondria

completes breakdown of glucose

by decomposing a derivative of pyruvic acid to carbon dioxide

contributes electrons to 3rd stage

produces 2 molecules of ATP

by substrate-level phosphorylation

produces other energy-rich molecules

Stages of Cellular Respiration

Electron transport chain

3rd stage

takes place in the mitochondria

chain uses downhill flow of electrons from electron carriers to oxygen

uses that energy to pump hydron ions across membrane
which provides energy for ATP synthase to make ATP by chemiosmosis

Photosynthesis:
Using Light to Make Food

Photosynthesis uses light energy to make food molecules

Photosynthesis

most of living world depends on the food-making machinery of this process

on a global scale - billions of tons of organic matter are produced each year by this process
no other chemical process of Earth matches this output

consists of two stages that occur in the chloroplast

Autotrophs are the producers of the biosphere

Plants are autotrophs

"self-feeders"

make own food
sustain themselves

without eating other organisms or organic molecules

chloroplasts capture energy in sunlight

and with water and carbon dioxide convert sun’s energy to chemical energy
stored in form of glucose and other organic molecules

Autotrophs are the producers of the biosphere

Producers are the organisms that produce the food consumed by heterotrophs

all organisms that use light energy to make food molecules from inorganic molecules are

producers

photosynthetic autotrophs

producers include

plants
certain archaea
certain bacteria
certain protists

Autotrophs are the producers of the biosphere

Predominant producers

terrestrial

plants such as trees

aquatic

photosynthetic protists (algae)
photosynthetic bacteria

Photosynthesis occurs in chloroplasts

All green parts of a plant have chloroplasts and can carry out photosynthesis

in most plants, leaves have most chloroplasts

are major sites of photosynthesis

green color in plants is from chlorophyll pigments in chloroplasts

chloroplhyll absorbs light energy from sun

Photosynthesis occurs in chloroplasts

Green tissue in interior of leaf is called mesophyll

each mesophyll cell has numerous chloroplasts

membranes in the chloroplast form the structural framework where many reactions of photosynthesis occur
inner membrane encloses a compartment filled with a thick fluid called stroma
within the stroma, disklike membranous sacs called thylakoids are suspended

thylakoids are concentrated in sacks called grana

Plants produce O₂ gas by splitting water

Photosynthesis equation

CO₂ + H₂O ® light® C₆ H₁₂O₆ + H₂O + O₂

Photosynthesis is a redox process, as is cellular respiration

Photosynthesis is a redox process

water is oxidized to O₂

when water molecules are split apart
they lose electrons & hydrogen ions

CO₂is reduced to sugar

when electrons & hydrogen ions are added to it

Photosynthesis is a redox process, as is cellular respiration

Photosynthesis is a redox process

water is oxidized & carbon dioxide is reduced

electrons gain energy by being boosted up an energy hill

converts light energy to chemical energy

Cellular respiration is a redox process

sugar is oxidized and oxygen is reduced

electrons lose energy as they travel down an energy hill

converts chemical energy from one form to another

Photosynthesis occurs in two stages

Photosynthesis is not a single process

has two stages, each with multiple steps

light reactions
first stage
converts light energy to chemical energy and oxygen gas

Calvin cycle
second stage
assembles sugar molecules using CO₂ and energy-containing products of the light reactions

Photosynthesis occurs in two stages

Light reactions

occur in thylakoid membranes

absorb solar energy & convert it to chemical energy by

making ATP from ADP + P

transferring electrons from H₂O to NADP⁺ to form NADPH

electron carrier similar to NAD⁺

notice that no sugar is produced during these reactions

requires light

Photosynthesis occurs in two stages

Calvin cycle

occurs in stroma of chloroplasts

carries out process of carbon fixation

incorporation of the C from CO₂ into organic compounds

enzymes of the cycle then make sugars by further reducing the fixed carbon

by adding high-energy electrons and hydrogen ions to it

does not require light directly

but occurs during day in most plants

Photosynthesis uses light energy to make food molecules

light reactions

occur in thylakoid membrane

photosystems I & II capture solar energy and energize electrons

water is split and O₂ is released

photosystems transfer electrons to ETCs

where energy is harvested and used to make NADPH and ATP

Photosynthesis uses light energy to make food molecules

Calvin cycle

occurs in stroma

incorporates carbon from CO₂ in the air into the 3 carbon sugar G3P

G3P is used to make sugars which are

used as fuel for cellular respiration
used as starting material for other organic molecules such as cellulose
stored as starch in chloroplasts, roots, tubers, fruits