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Unit 2
Why is Food so Important?
Why do you eat?
Food is taken in, taken apart, and taken up in the process of animal __________________________
In general, animals fall into three categories:
__________________________ eat mainly plants and algae
__________________________ eat other animals
__________________________ regularly consume animals as well as plants or algae
Most animals are also _____________________________________ feeders
An animal’s diet must supply chemical energy, organic molecules, and essential nutrients
Chemical energy
Organic building blocks
Essential nutrients
Major classes of nutrients
__________________________
Primary source of _____________ for the body, especially for the brain and physical activity.
Provide ___ kcal per gram.
Carbohydrates are found in grains (wheat, rice), vegetables, fruits, and legumes (lentils,
beans, peas), milk products.
____________________________
Include triglycerides, phospholipids, sterols.
An important energy source during ____________ or ________________________ exercise.
Provide _____ kcal per gram.
________________________ as adipose tissue (body fat).
Provide fat-soluble vitamins and essential _____________________________.
Essential Fatty Acids
Animals can synthesize _________________________ of the fatty acids they need
The essential fatty acids must be ____________________ from the diet and include
certain unsaturated fatty acids (i.e., fatty acids with one or more double bonds)
Deficiencies in fatty acids are __________________
___________________________
Proteins are important for
Provide ___kcal per gram.
Protein sources include meats, dairy products, seeds, nuts, and legumes.
Essential Amino Acids
Animals require ____ amino acids and can synthesize about half from molecules in their diet
The remaining amino acids, the essential amino acids, must be obtained from ____________ in
preassembled form
Meat, eggs, and cheese provide all the essential amino acids and are thus “complete” proteins
Most plant proteins are _____________________ in amino acid composition
Individuals who eat only plant proteins need to eat specific plant combinations to get all
the essential amino acids
Some animals have adaptations that help them through periods when their bodies demand
extraordinary amounts of protein
_____________________________
Vitamins are _______________________ molecules that assist in regulating body processes:
critical in building and maintaining healthy _______________ and __________________
support _____________________ system
ensure healthy _____________________
Vitamins do not supply _____________________ to our bodies
Thirteen vitamins are essential for humans
Vitamins are grouped into two categories: fat-soluble and water-soluble
Fat-soluble vitamins & Water-soluble vitamins
Fat-soluble vitamins can be __________________ in the body.
Daily or weekly intake ______________ necessary
Deficiency _________________ common
Large intakes can result in ___________________
Excess water-soluble vitamins are eliminated by the kidneys and cannot be stored in our bodies.
Regular intake required to avoid _________________________
Toxicity rarely occurs
______________________________
Minerals are simple ______________________ nutrients, usually required in small amounts
Ingesting large amounts of some minerals can upset homeostatic balance
Minerals have physiological functions, such as
_______________________________
Inorganic nutrient, essential for survival
Involved in many body processes:
fluid _______________ and nutrient ___________________; nerve impulses; body
____________________; removal of _________________; muscle contractions;
chemical __________________
What about Alcohol?
____________________________
Various distilled products and drugs
Provides some energy
Energy yielding (____Kcal/g)
Why is it not a nutrient?
What is part of the Digestive Process?
The main stages of food processing are ingestion, digestion, absorption, and elimination
________________________ is the act of eating
________________________ is the process of breaking food down into molecules small
enough to absorb
_______________________ digestion, including chewing, increases the surface area of food
_______________________ digestion splits food into small molecules that can pass
through membranes; these are used to build larger molecules
In chemical digestion, the process of _______________________________________
splits bonds in molecules with the addition of water
___________________________ is uptake of nutrients by body cells
___________________________ is the passage of undigested material out of the digestive system
Now let’s get into more detail about how nutrients provide our bodies with energy
The Energy of Life
The living cell is a miniature _____________________ factory where thousands of reactions occur
The cell ____________________ energy and __________________ energy to perform ___________
Some organisms even convert energy to light, as in bioluminescence
Two basic forms of energy
______________________ energy is the energy of _____________________
______________________ energy is _____________________ energy
Additional forms of energy
Thermal energy
Chemical energy
Two laws govern energy transformations
Thermodynamics is the study of ________________________________________
The First Law of Thermodynamics
the energy of the universe is constant
The first law is also called the ______________________________________________
The Second Law of Thermodynamics
During every energy transfer or transformation, some energy is ____________________,
and is often lost as ______________________
According to the second law of thermodynamics
What is metabolism?
____________________________________________ that is carried out by cells
Metabolism is an emergent property of life that arises from interactions between molecules
within the cell
Metabolic Pathways
A metabolic pathway begins with a specific molecule and ends with a __________________
Each step is _________________________ by a specific _____________________
Two basic pathways in order to convert energy
Catabolic pathway
Ex. cellular respiration, burning
Anabolic pathway
Ex. photosynthesis
The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously
Biologists want to know which reactions occur spontaneously and which require input of energy
To do so, they need to determine energy ________________ that occur in chemical reactions
Free-Energy Change, ∆G
A living system’s free energy is
The change in free energy (∆G) during a process is related to the change in _____________,
or change in total energy (∆H), change in entropy (∆S), and temperature in Kelvin (T)
∆G = ∆H – T∆S
Only processes with a _________________________ ∆G are spontaneous
Spontaneous processes can be harnessed to perform ____________________
Exergonic and Endergonic Reactions and Metabolism
An ________________________ reaction proceeds with a net release of free energy and is
____________________________
An ________________________ reaction absorbs free energy from its surroundings and is
___________________________
Molecules Important for metabolic reactions
_______ powers cellular work by _____________________ exergonic reactions to endergonic reactions
A cell does three main kinds of work
To do work, cells manage energy resources by ______________________________, the use
of an exergonic process to drive an endergonic one
Most energy coupling in cells is mediated by _____________
The Structure and Hydrolysis of ATP
ATP (adenosine triphosphate) ____________________ nearly all forms of cellular work
ATP is composed of ________________ (a sugar), ___________________ (a nitrogenous base),
and three ______________________ groups
The bonds between the phosphate groups of ATP’s tail can be broken by ____________________
Energy is released from ATP when the terminal phosphate bond is _____________________
This release of energy comes from the chemical change to a state of ____________________
free energy, ___________ from the phosphate bonds themselves
How the Hydrolysis of ATP Performs work
The three types of cellular work (mechanical, transport, and chemical) are powered by the
hydrolysis of ATP
Let’s first look at chemical work
_________________________ Work
In the cell, the energy from the ___________________________ reaction of ATP hydrolysis
can be used to drive an ____________________________ reaction
ATP drives endergonic reactions by __________________________, transferring a
phosphate group to some other molecule, such as a ___________________________
The recipient molecule is now called a _________________________________________
Transport Work
Mechanical Work
The Regeneration of ATP
ATP is a __________________________ resource that is regenerated by addition of a phosphate
group to adenosine diphosphate (_________)
The energy to phosphorylate ADP comes from ________________________ reactions in
the cell
The ATP cycle is a _____________________________ door through which energy
passes during its transfer from catabolic to anabolic pathways
What is an Enzyme?
Enzymes speed up metabolic reactions by lowering energy barriers
A ______________________ is a chemical agent that speeds up a reaction without being
consumed by the reaction
An ___________________________ is a catalytic protein
Hydrolysis of sucrose by the enzyme sucrase is an example of an enzyme-catalyzed reaction
How?
Enzymes help to ____________________________ energy of activation
Energy of activation (____ )
Substrate Specificity of Enzymes
The reactant that an enzyme acts on is called the enzyme’s ________________________
The enzyme binds to its substrate, forming an ___________________________________________
The _____________________________ is the region on the enzyme where the substrate binds
_____________________________ of a substrate brings chemical groups of the active site
into positions that enhance their ability to catalyze the reaction
Effects of Local Conditions on Enzyme Activity
An enzyme’s activity can be affected by
General environmental factors, such as _____________________________ and _______
Chemicals that specifically influence the enzyme
Effects of Temperature and pH
Each enzyme has an _______________________ temperature in which it can function
Each enzyme has an optimal ________ in which it can function
Optimal conditions favor the most active __________________ for the enzyme molecule
Cofactors
__________________________ are nonprotein enzyme helpers
Cofactors may be ___________________ (such as a metal in ionic form) or ________________
An organic cofactor is called a _____________________
Coenzymes include ___________________________
Enzyme Inhibitors
__________________________________________________ bind to the active site of
an enzyme, competing with the substrate
__________________________________________________ bind to another part of an
enzyme, causing the enzyme to change shape and making the active site less effective
Examples of inhibitors include toxins, poisons, pesticides, and antibiotics
With a Foundation of metabolism, let’s focus on the question:
If your cells need energy to survive and function, where do they get it?
Photosynthesis and cellular respiration provide __________________ for life
All living organisms require energy to maintain _______________________, to ____________,
and to _______________________
Photosynthesis converts energy from the ______________ to ___________________ and ______
Cellular respiration breaks down __________________________ and releases energy in ________
Cellular respiration banks energy in ATP molecules
The reactants _______ and ___________________________ regroup to form the products __________
and ____________
Energy from glucose is _____________________________ and stored in _________________
Cells tap energy from electrons “_________________________” from organic fuels to oxygen
The energy available to a cell is contained in the arrangement of electrons in ______________________
Electrons lose potential energy when they “fall” from __________________________________
to ____________________________________ during cellular respiration
Each step of the “fall” involves paired _____________________________________ (redox) reactions
Oxidation:
Reduction:
The electron donor is called the ________________________________________
The electron receptor is called the ____________________________________________
Some redox reactions do ________ transfer electrons but change the electron sharing in covalent bonds
An example is the reaction between methane and O2
The redox reactions of cellular respiration
Glucose ___________________ electrons (in H atoms) and becomes ______________________
O2 __________________ electrons (in H atoms) and becomes ________________________
Along the way, the electrons lose potential energy, and energy is _________________________
The redox reactions that break down glucose involve an enzyme and a coenzyme
The enzyme ________________________________________ removes electrons (in H
atoms) from fuel molecules (oxidation)
The electrons are transferred to the coenzyme ________, which is converted to NADH (reduction)
NADH passes electrons to an electron transport chain
As electrons “_______” from carrier to carrier and finally to O2, energy is released in small quantities
The energy released is used by the cell to make ____________
Stages of Cellular Respiration and Fermentation
Cellular respiration occurs in three main stages
Overview
Stage 1: __________________________
Occurs in the _______________________________
Breaks down glucose into ______________________, producing a small amount of ATP
Stage 2: _____________________________________________
Takes place in the __________________________________________
Completes the breakdown of glucose, producing _____________ and a small amount of ______
Supplies the third stage of cellular respiration with electrons
Stage 3: _____________________________________________
Occurs in the _____________________________________
Uses the energy released by electrons “falling” down the _____________________________
to pump H+ across a membrane
Harnesses the energy of the H+ gradient through chemiosmosis, producing ATP
Oxidative phosphorylation accounts for almost _____% of the ATP generated by cellular
respiration
A smaller amount of ATP is formed in glycolysis and the citric acid cycle by
____________________________________________
For each molecule of glucose degraded to _____________ and water by respiration, the cell
makes up to _________ molecules of ___________________________
Glycolysis harvest chemical energy by oxidizing glucose to pyruvate
Glycolysis occurs in the cytoplasm and has two major phases
Glycolysis occurs whether or not _______ is present
Glycolysis __________________ sugar molecules in the cytoplasm
Starts with a single 6-carbon molecule of _________________________
Ends with two 3-carbon molecules of __________________________
Yeilds ______ molecules of _____________ in the process and 2 __________________
Pyruvate is chemically ____________________ for the citric acid cycle
A large, multienzyme complex catalyzes three reactions in the mitochondrial matrix
A carbon atom is ________________ from pyruvate and released in ___________
The remaining two-carbon compound is _______________________, and a molecule of NAD+
is reduced to ________________________
Coenzyme ___ joins with the 2-carbon group to produce _____________________
The citric acid cycle completes the oxidation of organic fuel, generating many NADH and
FADH2 molecules
For each turn of the citric acid cycle
Two _________molecules are released
The energy yield is one ____________, three _________, and one ___________
The citric acid cycle has eight steps, each catalyzed by a specific ___________________
The acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate, forming citrate
The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle
The NADH and FADH2 produced by the cycle _____________ electrons extracted from
food to the ________________________________________
During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis
Following glycolysis and the citric acid cycle, NADH and FADH2 account for most of
the energy ______________________ from ___________________
These two electron ________________________________ donate electrons to the electron
transport chain, which powers ATP synthesis via oxidative _____________________________
The Pathway of Electron Transport
The electron transport chain is in the inner membrane (_________________) of the mitochondrion
Most of the chain’s components are _________________, which exist in multiprotein complexes
The carriers alternate reduced and oxidized states as they accept and donate ____________________
Electrons drop in free energy as they go down the chain and are finally passed to O2,
forming ___________________________
Electrons are transferred from NADH or FADH2 to the ______________________________
Electrons are passed through a number of proteins including __________________________
(each with an iron atom) to ___________
The electron transport chain generates no ___________________________ directly
It breaks the large free-energy drop from food to O2 into smaller steps that release
energy in ________________________________ amounts
_______________________________________: The Energy-Coupling Mechanism
Electron transfer in the electron transport chain causes proteins to pump H+ from the
mitochondrial matrix to the intermembrane space
H+ then moves back across the membrane, passing through the proton, _______________________
ATP synthase uses the exergonic flow of _________ to drive phosphorylation of _________
This is an example of ________________________, the use of energy in a H+ gradient to
drive cellular ______________
The energy stored in a H+ gradient across a membrane couples the _____________ reactions of the
electron transport chain to ATP synthesis
The H+ gradient is referred to as a ______________________________ force, emphasizing
its capacity to do work
Acounting of ATP Production by Cellular Respiration
During cellular respiration, most energy flows in this sequence:
About 34% of the energy in a glucose molecule is transferred to ATP during cellular
respiration, making about 32 ATP
There are several reasons why the number of ATP is not known exactly
Fermentation eneables cells to produce ATP _______________________ oxygen
__________________________________
Generates two ATP molecules from glycolysis in the ____________________ of oxygen
Recycles NADH to NAD+ _______________________________
Muscle cells use _______________________________ fermentation
NADH is oxidized to NAD+ as pyruvate is reduced to ________________________
Alcohol fermentation occurs in brewing, wine making, and bakintg
NADH is oxidized to NAD+ while converting pyruvate to CO2 and _________________
Comparing Fermentatition with Anaerobic and Aerobic Respiration
Cellular respiration produces ____ATP per glucose molecule; fermentation produces ____ATP
per glucose molecule
___________________________ carry out fermentation or anaerobic respiration and cannot
survive in the presence of O2
Yeast and many bacteria are _______________________________________, meaning that
they can survive using either fermentation or cellular respiration
In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative
___________________________________________
Glycolysis and the citric acid cycle connect to many other metabolic pathways
Gycolysis and the citric acid cycle are major ________________________ to various
catabolic and anabolic pathways
The Versatility of Catabolism
Catabolic pathways funnel electrons from many kinds of ______________________________
into cellular respiration
Glycolysis accepts a wide range of carbohydrates
Proteins must be digested to ____________________; amino groups can ______________
glycolysis or the citric acid cycle
Fats are digested to _________________ (used in glycolysis) and ______________________
(used in generating acetyl CoA)
Fatty acids are broken down by ____________________________ and yield acetyl CoA
An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of
carbohydrate
Biosynthesis (Anabolic Pathways)
The body uses small molecules to ________________________ other substances
These small molecules may come directly from ________________, from
____________________, or from the _____________________________
Where Does Our Food Come From?
The fuel for respiration ultimately comes from ______________________________________
All organisms can harvest energy from ____________________________ molecules
These organisms are usually referred to as _________________________________
Plants can also make molecules from __________________________ sources by photosynthesis
The organisms are referred to as _____________________________
Photosynthesis converts light energy to the chemical energy of food
_____________________________ are structurally similar to and likely evolved from
photosynthetic bacteria
The structural organization of these cells allows for the chemical reactions of ___________________
Chloroplasts: The Sites of Photosynthesis in Plants
___________________________ are the major locations of photosynthesis
Their green color is from __________________, the green pigment within chloroplasts
Chloroplasts are found mainly in cells of the ______________________________, the interior
tissue of the leaf
Each mesophyll cell contains _____________ chloroplasts
CO2 enters and O2 exits the leaf through microscopic pores called ____________________
The chlorophyll is in the membranes of ______________________ (connected sacs in the
chloroplast); thylakoids may be stacked in columns called ____________________
Chloroplasts also contain ___________________, a dense interior fluid
Tracking Atoms Through Photosynthesis
Photosynthesis is a complex series of reactions that can be summarized as the following
equation:
The Splitting of Water
Chloroplasts split __________ into hydrogen and oxygen, incorporating the electrons of hydrogen into
sugar molecules and releasing ____________ as a by-product
Photosynthesis as a Redox Process
Photosynthesis _______________________ the direction of electron flow compared to respiration
Photosynthesis is a redox process in which H2O is _________________ and CO2 is ______________
Photosynthesis is an _________________________ process; the enery boost is provided by __________
Photosynthesis occurs in two stages linked by ATP and NADPH
Overview
____________________________ reactions
Occur in _____________________ membranes
Convert light energy to chemical energy as _____________ and _________________
Produce _________________ as a waste product
__________________________ cycle
Occurs in _________________
Assembles __________________ molecules from _____________ using _____________
and _________________ from light reactions
Light Reactions: Coverting Solar Energy to Chemical Energy
Visible radiation drives the light reactions
Light is a form of electromagnetic energy, also called ___________________________________
Like other electromagnetic energy, _____________________ travels in rhythmic waves
_______________________________ is the distance between crests of waves
Wavelength determines the _________________________ of electromagnetic energy
The _______________________________________ is the entire range of electromagnetic
energy, or radiation
__________________________________ consists of wavelengths (including those that
drive photosynthesis) that produce colors we can see
Light also behaves as though it consists of discrete particles, called ____________________
How is light absorbed?
_____________________________________ pigments
__________________ some wavelengths of light; ______________ or _______________ others
Types of pigments
_____________________________________
Absorbs blue-violet and red light, reflects green light
Participates directly in the light reactions
_____________________________________
Absorbs blue and orange light, reflects yellow-green
Conveys absorbed energy to chlorophyll a
______________________________________
Yellow-orange pigments that absorb mainly blue-green light
May pass energy to chlorophyll a or protect it by dissipating excessive light energy
Light also behaves as photons
A
Specific amounts of ________________________ in photons absorbed by different pigments
The _________________ the wavelength of a photon, the ____________________ amount of
energy that photon possesses
Photosystems captur solar power
The thylakoid membrane contains two types of _______________________, which consist of
Light-harvesting complexes of chlorophyll and other pigments and proteins
Photosystems
Pigment molecules (which capture photons) surrounding a ______________________________
that contains
A____________________________________ molecule
A _____________________________________________________ molecule
That will transfers them to an electron transport chain
Linear Electron Flow
During the light reactions, there are two possible routes for electron flow:
_______________________ electron flow, the primary pathway, involves both
photosystems and produces ATP and NADPH using _________________ energy
A ___________________ hits a pigment and its energy is passed among pigment molecules until
it excites P680
An excited electron from P680 is transferred to the primary electron acceptor (we now call it P680+)
P680+ is a very strong ___________________ agent
H2O is ______________ by enzymes, and the electrons are transferred from the hydrogen
atoms to P680+, thus reducing it to P680
O2 is ___________________________________ as a by-product of this reaction
Each electron “falls” down an electron transport chain from the primary electron acceptor of
PS______ to PS______
Energy released by the fall drives the creation of a proton ______________________ across
the thylakoid membrane
____________________________ of H+ (protons) across the membrane drives ATP synthesis
In PS I (like PS II), transferred light energy excites P700, which _____________ an electron
to an electron acceptor
P700+ (P700 that is missing an electron) _________________________ an electron passed
down from PS II via the electron transport chain
Each electron “falls” down an electron transport chain from the primary electron acceptor of
PS I to the protein ferredoxin (Fd)
The electrons are then transferred to NADP+ and reduce it to _______________________
The electrons of NADPH are available for the reactions of the ____________________ cycle
This process also removes an H+ from the _____________________
Cyclic Electron Flow
_____________________ electron flow uses only photosystem I and produces ATP, but not
NADPH
No _________________________ is released
Cyclic electron flow generates surplus ATP, satisfying the higher demand in the Calvin cycle
The Calvin cycle uses the chemical energy of ATP and NADPH to reduce CO2 to sugar
The Calvin cycle, like the citric acid cycle, ___________________________________ its
starting material after molecules enter and leave the cycle
The cycle ____________________ sugar from smaller molecules by using ATP and the
reducing power of electrons carried by ___________________
Carbon enters the cycle as CO2 and leaves as a sugar named
For net synthesis of 1 G3P, the cycle must take place _____ times, fixing 3 molecules of CO2
The Calvin cycle has three phases
C4 and CAM plants have special adaptations that save __________________
What happens when the environment is hot and dry?
___________________________ will occur
__________ plants
Corn, soybeans, wheat, rice
Use CO2 __________________________
Rate of photosynthesis decreases in dry weather
Stomata _______________, CO2 supply ________________________
Calvin cycle diverted to ________________________________
___________ plants
Include corn and sugarcane
CO2 fixed into a 4-carbon compound that acts as a carbon shuttle
Enables plant to continue making sugar
Prevents photorespiration and water loss
___________ plants
Some plants, including succulents, use crassulacean acid metabolism (______) to fix carbon
Adapted to very dry climates
Open stomata and admit CO2 only at ______________________
Fix CO2 into a 4-carbon compound that banks CO2 for release to Calvin cycle during the day
Let’s describe some reasons why photosynthesis is important to you.
Photosynthesis moderates __________________________________
The ________________________ effect
Like a greenhouse, the atmosphere traps CO2 and other gases that absorb heat radiated
from Earth's surface
Excess greenhouse gases in the atmosphere contribute to global warming
Photosynthesis, which removes CO2 from the atmosphere, moderates warming
Mario Molina talks about Earth’s protective ___________________ layer
Nobel Prize winner Mario Molina has studied how pollutants are affecting Earth's ozone layer
Solar radiation converts O2 high in the atmosphere to ozone (_____)
The ozone layer shields organisms on Earth's surface from damaging UV radiation
CFCs have caused dangerous thinning of the ozone layer
International restrictions on __________ use are allowing a slow recovery