BIOCHEMICAL
PROCESSED IN CELLS:
REVISION
Exam revision – what should I be
doing???
• Whole exam papers under exam conditions
(preferably at 9-10.45am) – at least 4-10
• Preparing posters, revision cards etc
• Jacplus study on questions
• Testing each other…..
Key knowledge
• the nature of biochemical processes
• enzymes as organic catalysts
• energy requirements of cells; catabolic and
anabolic reactions
• energy transformations, including main stages
in and sites of photosynthesis and cellular
respiration; ATP-ADP cycle; factors affecting
rate of energy transformations
Quiz
• In an endergonic/anabolic reaction, is energy
released or required?
• What are the overall equations for
photosynthesis and respiration?
• How many stages are there in photosynthesis,
what are their names and where do they
occur?
• How many stages are there in cellular
respiration, what are their names and where
do they occur?
Chemical reactions
• All chemical reactions are:
– Energy dependent
– Occur faster at higher temperatures
Chemical reactions within cells
• Cell metabolism includes all the chemical
reactions that take place in order to
maintain growth and normal functioning
• The reactions take place in a series of
steps called BIOCHEMICAL PATHWAYS
Chemical reactions within cells
Large molecules are broken
down into smaller
molecules releasing energy
in the form of ATP
Figure 3.7
Large molecules made from
smaller molecules requiring
energy in the form of ATP
Chemical reactions within cells
• The chemical reactions can be:
Catabolic (exergonic) Anabolic
(endergonic)
Energy?
ATP?
Molecule size
Example
Chemical reactions within cells
• The chemical reactions can be:
Catabolic (exergonic)
Anabolic
(endergonic)
Energy?
Release energy
Require energy
ATP?
Generate ATP
Use ATP
Molecule size Large molecules are broken
down into smaller
molecules
Large molecules
made from smaller
molecules
Example
E.g. DNA synthesis
from nucleotides
E.g. cellular respiration –
glucose broken down into
CO2 and water
Catalysts
• All reactants need to have a certain amount of
energy before they will react
• This is called the energy barrier or ACTIVATION
ENERGY
• All catalysts lower the activation energy
needed, allowing reactions to occur more
rapidly
Enzymes as catalysts
• ENZYMES are globular proteins that act as
catalysts in BIOCHEMICAL PATHWAYS
– Each step is controlled and regulated by a specific
enzyme
– Most enzyme activity is intracellular – digestive
enzymes are an exception
– Enzymes are involved in both the breakdown and
synthesis of molecules
Enzymes lower activation energy
Figure 3.8 Enzymes reduce the amount of energy required to begin the reactions they
catalyse. Note the difference in energy requirement with and without an enzyme.
Enzyme Structure
• Made of proteins (and sometimes other
substances called co-enzymes or co-factors)
folded to have an active site
• The R groups of the amino acids in an
enzyme line the ACTIVE SITE to form
molecular interactions with the SUBSTRATE
Enzymes structure
Coenzymes and cofactors
• Co-enzymes:
– Small organic non-protein molecules
– Assist by binding to enzymes or by carrying
electrons or protons
– May also carry specific atoms or groups of atoms
required for or produced by chemical reactions
• Co-factors:
– Metal cations (i.e. positively charged ions)
– Bind to enzyme and increase rate of reaction
Common Coenzymes
Coenzyme
Loaded form
Unloaded form
Function
Adenosine
triphosphate
ATP
ADP
Energy transfer
Nicotine adenine
dinucleotide
NADH
NAD+
Transfer of
electrons and
protons (i.e. H+)
Nicotine adenine
dinucleotide
phosphate
NADPH
NADP
Transfer of
electrons and
protons (i.e. H+)
Flavine adenine
dinucleotide
FADH2
FAD
Transfer of
electrons and
protons (i.e. H+)
Models of Enzyme action
• There are two models of enzyme action:
1. Lock and key model
• The shape of the active site is complementary to the
shape of the substrate molecule(s)
Models of Enzyme action
2. Induced fit model
• The shape of the active site changes when the
substrate binds to it. The substrate molecule(s) induces
a better fit. (think baseball and glove)
ATP vs ADP
ATP
• 3 phosphates
• Stored energy (highly
energetic with sunlight)
• A charged battery to
living things
ADP
• 2 phosphates
• Less energetic (without
sunlight)
• Needs to be ‘recharged’ to provide
energy
• Produced with NADPH • Produced with NADP+
Enzyme action –
catabolic reactions
Catabolic reactions: ADP -> ATP
• The energy released by a catabolic reaction is
used to add a phosphate group to ADP,
forming ATP: PHOSPHORYLATION
Catabolic
reaction
ENERGY
P
ADP
ATP
Enzyme action –
anabolic reactions
ENERGY
Anabolic reactions: ATP -> ADP
• The energy released from the
HYDROLYSIS of ATP into ADP and P is
used to drive anabolic reactions
ATP
Anabolic
reaction
ENERGY
ADP
P
Optimum conditions for enzyme action
• Every enzyme has its own optimum temperature
and pH
• Outside the optimum conditions, intermolecular
bonds are broken leading to a change in the active
site and a loss of function
• This is called DENATURING the enzyme
• Some enzymes can regain their shape, while in
others the changes are irreversible.
Optimum conditions for enzyme action: pH
Optimum conditions for Enzyme
action: TEMPERATURE
Enzyme inhibition
• Enzyme action can be affected by the
presence of other molecules which
may inhibit the action of the enzyme
• Can be reversible or irreversible, and
can sometimes cause death
Reversible enzyme inhibition: Competitive
•
Molecule competes with the substrate for the
enzyme’s active site
•
Binds temporarily with the active site, preventing the
binding of the enzyme and substrate
INHIBITOR
SUBSTRATE
ENZYME
Irreversible enzyme inhibition: Competitive
Molecule bonds covalently (ie strongly) to
the enzyme’s active site causing
permanent loss of activity
Such molecules are toxic to cells
Heavy metal ions, nerve gases and natural
toxins are irreversible inhibitors
INHIBITOR
SUBSTRATE
ENZYME
Non-competitive enzyme inhibition
• Molecule which binds with enzyme on
another part of the molecule (not the
active site)
• Alters the shape of the enzyme and the
ability of the active site to bind with the
substrate molecule
• Can be reversible or irreversible
Make sure you review!!!
Experimental Design
• http://www.slideshare.net/mrmularella/exper
imental-design
DV
Photosynthesis
A light dependent reaction that involves
•trapping the radiant energy of sunlight by
pigments such as CHLOROPHYLL
•converting it to chemical energy in the form of
GLUCOSE
What’s missing from the
diagram to the right?
Photosynthesis
A two-stage process
Photosynthesis Summary
STAGE
LOCATION
WHAT IS HAPPENING?
INPUTS
OUTPUTS
REACTION
TYPE
Photosynthesis Summary
STAGE
LOCATION
WHAT IS HAPPENING?
INPUTS
OUTPUTS
REACTION
TYPE
Light
dependent
Granum of
chloroplast
Absorption of light by
chlorophyll (or other
pigments) and conversion of
light energy to chemical
energy (ATP)
H2O
ADP + Pi
NADP+
NADPH
O2
ATP
Catabolic
(HAPN+)
(NOA)
Combining carbon dioxide
(from the air or cellular
respiration) with hydrogen
(from NADPH) to form
glucose in a series of
reactions called the Calvin
Benson (CB) cycle
NADPH
ATP
CO2
NADP+
ADP + Pi
C6H12O6
(NAC)
(CAPN+)
Light
independent
Stroma of
chloroplast
Anabolic
Location: Chloroplast
LIGHT-INDEPENDENT
STAGE
LIGHT-DEPENDENT STAGE
Light-dependent stage
Light-independent (synthesis) stage
The light-independent stage of
photosynthesis can be represented by
the equation:
http://www.gtac.edu.au/site/gcasts/UNIT3/photosynthesis/index.html
C3 & C4 plants
• C3 plants major producers in temperate and
polar forests and ecosystems (e.g. legumes
and wheat)
• C4 plants major producers in warm or hot
desert and grassland ecosystems (e.g. sugar
cane and corn)
Cellular respiration
• A series of reactions that take place in the
mitochondria and release energy from organic
molecules, such as glucose, and transfers it to ATP
• Occurs all the time in cells of ALL living things –
plants, animals, fungi, protists and bacteria
Aerobic cellular respiration
• Can be summarised by the equation:
• Occurs in three stages:
Cellular Respiration Summary
STAGE
LOCATION
WHAT IS HAPPENING?
INPUTS
OUTPUTS
REACTION
TYPE
Cellular Respiration Summary
STAGE
LOCATION
WHAT IS HAPPENING?
INPUTS
OUTPUTS
REACTION
TYPE
Glycolysis
Cytosol
6-C glucose is split into two
3-C pyruvate molecules,
releasing energy
C6H12O6
2-4 ADP +
Pi
2 NAD+
2 pyruvate
2-4 ATP
2 NADH
Catabolic
Krebs cycle
Matrix of
mitochondria
3-C pyruvate is broken down
and 3 molecules of CO2 are
formed (i.e. 6 in total from 2
pyruvates)
2 pyruvate
2 ADP + Pi
8 NAD+
2 FAD
6 CO2
2 ATP
8 NADH
2 FADH2
Catabolic
Electron
transport
Inner
membrane of
mitochondria
Electrons from the loaded
NADH and FADH2 molecules
are transferred from one
cytochrome to another and
finally to oxygen to form
water
32 ADP +
Pi
O2
NADH
FADH2
32 ATP
H2O
NAD+
FAD
Catabolic
Glycolysis
Krebs cycle
Electron transport
Summary
• Aerobic respiration of one molecule of glucose
is couple to production of 36 -38 molecules of
ATP
http://www.gtac.edu.au/site/gcasts/UNIT3/cellular_respiration/index.html
Summary
http://www.gtac.edu.au/site/gcasts/UNIT3/cellular_respiration/index.html
Anaerobic cellular respiration
Anaerobic respiration
• Occurs in the cytosol of cells
• End product depends on the organism
– Lactate in animals
C6H12O6  2 lactic acid + 2 ATP
– Ethanol and carbon dioxide in yeasts
C6H12O6  2C2H3OH + 2CO2+ 2 ATP
http://img.sparknotes.com/figures/1/18b9012870c85fba3a8046a767b52ddf/anaerobicaerobic.gif
Anaerobic respiration
http://www.gtac.edu.au/site/gcasts/UNIT3/cellular_respiration/index.html
Quiz
• In an endergonic/anabolic reaction, is energy
released or required?
• What are the overall equations for
photosynthesis and respiration?
• How many stages are there in photosynthesis,
what are their names and where do they
occur?
• How many stages are there in cellular
respiration, what are their names and where
do they occur?