Transcript Lecture 24 (4/29/13) "The Food You Eat

Today
Last Homework due this Wednesday
Finish up:
Nerves: Na/K concentration gradient
Fats, Sugars, Food you need to survive.
Nerves
How (electrical) signal is transported along a nerve
http://www.biologymad.com/NervousSystem/nerveimpulses.htm
From Atoms to molecules
to macromolecules to you!
3-6 elements make up majority of you.
About 3 dozen organic compound
-- precursors of almost all biomolecules
Body (Cell) uses 4 types of small molecules
1. Amino acids– make up proteins
2. Nucleic acids—DNA, RNA
3. Fatty acids/Lipids-- membranes
4.Sugars/polysaccharides/Carbohydrates—
structural, food
What does body/cell uses 4 molecules for?
1. Building blocks
2. Energy Source
3. Information
Primarily made of 4 small molecules
1. Sugar: carbohydrate= (poly)saccharide
Monosaccharide (CH2O): has an -OH or =O
Most common
form: D-glucose:
But many isomers!
(Can generate an
enormous # of
isomers.)
2. Fatty Acid: long (CH2)n with a
Fat (Lipids): fatty acids, with Triglycerides: insoluble in H2O
3. Nucleotides
4. Amino Acids: H2CHRCOOH: R= 1 or 20 side groups
Minimal Requirements of Food
A complete diet must supply the elements;
carbon, hydrogen, oxygen, nitrogen,
phosphorus, sulfur, and at least 18 other
inorganic elements. The major elements are
supplied in carbohydrates, lipids, and protein.
In addition, at least 17 vitamins and water are
necessary. If an essential nutrient is omitted
from the diet, certain deficiency symptoms
appear.
http://www.elmhurst.edu/~chm/vchembook/5900verviewmet.html
We “burn” our food.
Fire
Wood— 50% cellulose: C, H2O
[C6 (H2O)5]n
Polysaccharide of glucose
[We can’t break down because of
linkage between glucose]
PE chem. bonds  KE, i.e. heat
Life is a slow burn
6 CH2O + O2  6 CO2 + H2O + energy
Most common
form: D-glucose:
But many isomers!
(Can generate an
enormous # of
isomers.)
Breakdown of Glucose 30-40 ATP at 20-25 kT / ATP
Burning vs. eating of sugars/food
Eating done in small steps–
each step leads to intermediate carrier
Figure 2-69: Schematic representation of the controlled stepwise
oxidation of sugar in a cell, compared with ordinary burning
(A) In the cell, enzymes catalyze oxidation via a series of small steps in
which free energy is transferred in conveniently sized packets to carrier
molecules—most often ATP and NADH. At each step, an enzyme
controls the reaction by reducing the activation energy barrier that has to
be surmounted before the specific reaction can occur. The total free
energy released is exacly the same in (A) and (B). But if the sugar was
instead oxidized to CO2 and H2) in a single step, as in (B), it would
release an amount of energy much larger than could be captured for
useful purposes. From: How Cells Obtain Energy from Food
Molecular Biology of the Cell.
Breakdown of food
1. Digestion: (Intestines
[outside], lysosomes
[inside cells, separated
by membranes]
polymer monomers
2. glycolysis:
(Mitochondria)
glucose (& other sugars)
pyruvate (+ some ATP,
NADH)
3. acetyl CoA CO2 +
H2O + 36 ATP’s.
Citric acid cycle
produces a lot of high
energy electrons in
NADH which are then
transferred through the
electron transport chain
to produce ATP (from
ADP).
3 stages
NAD
Roughly 109 molecules of ATP are in solution in a typical cell at
any instant, and in many cells, all this ATP is turned over (that is,
used up and replaced) every 1–2 minutes.
http://www.ncbi.nlm.nih.gov/books/NBK26882/
Amino Acids
1. Building blocks
-- Make proteins
2. Energy Source
-- Eat proteins
3. Information
-- Signaling between cells/nerves
Neurons (Nerve cells) and
Synapses
• Neuron:
– Building blocks
of nervous
systems.
• Soma
– Cell body
• Dendrites
– Collect signals
• Axon
– Sends signals
• Synapse
– Dendrite-axon
junctions
Image from wikipedia
Neurons transmit signals via synapses.
The Synapse
• Synapse
– Presynapse
(Axon)
– Postsynapse
(dendrite)
– Synaptic cleft
(~30 nm)
Informa
tion
flow
Presyn
apse
Ax
on
• Active zone
(PAZ)
– Vesicle release
• Postsynaptic
density (PSD)
Dendrite
250-500 nm
Postsynapse
– Receptors
– Scaffold proteins
• PSD size is 250
-500 nm
The PSD is small, comparable to the light diffraction
limit.
Super-resolution techniques are required for imaging
the PSD.
How does nerve impulse traveling down
the axon lead to vesicle fusion and
glutamate release?
The action potential travels down the axon to the terminal. Arrival
at the terminal causes membrane depolarization, which opens
voltage-dependent Ca2+ channels situated in the active zone
where the neurotransmitter vesicles are docked. Ca2+ binds to
proteins, mainly synaptotagmin (a presynaptic protein—see next
pg), which cause vesicle fusion mainly through an interaction of
synaptotagmin with the SNARE proteins.
Presynaptic
cell
Axon
Postsynaptic cell
Synaptic vesicle
containing Postsynaptic
neurotransmitter
membrane Vesicles &
1
Figure
48.15
Synaptic
cleft
Presynaptic
membrane
3
membrane
contains
SNARE proteins
which dimerize
w Ca2+
K
Ca2
2
Voltage-gated
Ligand-gated

2
Ca channelion channels
4
Na
Sugars = Carbohydrates
1. Building blocks
-- Make complex sugars… glucose,
glycogen (polymer of glucose
Holds your cells together--Extracellular space filled with sugars
Cellulose (if a plant)
2. Energy Source
-- Eat Hershey’s chocolate!
Glucose makes 30-40 ATPs
3. Information
-- A lot! Much information.
Signaling that you are different than
a pig.
Sugar is a carbohydrate (C + H2O)
Sucrose & Lactose broken down into Glucose
then into Pyruvate and then into ATP as energy.
With Enzyme
can digest!
If no Enzyme
can’t digest!
Interesting Details
about Energy Storage
Class evaluation
1. What was the most interesting thing you
learned in class today?
2. What are you confused about?
3. Related to today’s subject, what would you like
to know more about?
4. Any helpful comments.
Answer, and turn in at the end of class.