PROTEIN
Objectives
2. Investigate the properties of carbohydrates, lipids,
and proteins.
2.4 Describe the relationship between amino
acids and proteins with reference to the peptide
bond.
2.5 Discuss enzymes using a series of key
words which should be included in a concept web
with the heading of proteins. (The key words are
substrate, enzyme)substrate complex, lock and key,
catalyst, factors affecting enzyme activity
[temperature; relative concentration of substrate],
enzymes, and coenzymes.)
2.7 Recognize the value of proteins by using
examples from the human body.
Why are proteins important?
• Proteins are one of the key building blocks of cells
and perform a wide range of functions.
Important structural molecules – collagen in muscles
and connective tissues, keratin in hair and nails
• Involved in all metabolic activities
• Generate motion – myosin in muscle cells
• Some serve as hormones – chemical messengers
released by cells in the body that influence cellular
activity in other parts of the body
• Transport oxygen – hemoglobin in red blood cells
• Defense – antibodies produced by the immune system
• Source of energy – excess proteins in diet are
decomposed as an energy sources
•
What is a protein?
• Proteins are the most complex of all nutrients
• They are made up of smaller molecules called amino
acids. There are 20 different amino acids that
organisms use to build proteins. The human body can
synthesis 12 of these amino acids, but must obtain the
other 8 from food sources. The 8 that must be
obtained are called essential amino acids
• Amino acids consist of a central carbon atom attached
to a single hydrogen atom; and amino acid group
(H2N), a carboxyl group (COOH) and a side chain
(represented by R) that varies among the 20 different
amino acids.
• A protein is formed when many amino acids are joined
together
H
|
…H2N – C – COOH…
|
R
H H O H H O
| | || | | ||
… –N–C–C–N–C–C–O–…
|
|
R
R
Where do proteins come
from?
• There are many plant and animal source of protein
• All animal sources of protein contain all 8 essential
amino acids.
•
Good sources of animal protein include dairy products,
eggs, and meats
• Most plant protein sources are missing at least one
essential amino acid. Therefore people who do not
eat animal protein must be sure to eat a large
combination of protein sources to get the essential
amino acids
•
Good sources of plant protein come from legumes
(beans), whole grains and nuts
Transamination
• Transamination refers to the transfer of an amine
group from one molecule to another
• The reaction is catalyzed by a family of enzymes
called transaminases
• The transamination results in the exchange of an
amine group on one acid with a ketone group on
another acid (analogous to a double replacement
reaction)
Structure of proteins
• There are four levels of protein structure
Primary structure – the sequential order of amino acids
• Secondary structure – the characteristic spiral shape
caused by the chain twisting. The two structures are the
alpha helix and the beta pleated sheet
• Tertiary structure – the spiral structure folds into a unique
three-dimensional shape caused by reactions between
the amino acids
• Quaternary structure: when polypeptides (short chains of
amino acid monomers linked by peptide bonds) bond to
form an even larger protein with a globular or fibrous
structure
•
Video:
https://www.youtube.com/watch?v=lijQ3a8yUYQ&sns=em
•
Video
•
https://www.youtube.com/watch?v=lijQ3a8yUYQ&sns=em
Denaturation
• Denaturation is a process in which proteins or
nucleic acids lose their tertiary structure and
secondary structure (uncoil and lose their shape) by
application of some external stress or compound.
These include
Addition of a strong acid or base
• A concentration of inorganic salt
• Heat
• Addition of heavy metals
• Addition of alcohol
•
• When a protein or amino acid has been denatured
they are no longer able to function
Limiting Amino Acids
• Limiting amino acids are essential
amino acids that are in short supply
in the body
• In order to relieve the effects of
limiting amino acids the body will
take two or more incomplete protein
sources to make a complete one in a
process called mutual
supplementation
Enzymes
• An enzyme is a protein which catalyzes functions in
the body.
•
A catalyst is a compound that speeds up the rate of
reaction but is not used up in the reaction
• Substrate – the compound that is changed in the
reaction with an enzyme
• Active site – the place where the substrate binds
with the enzymes
• Enzyme-substrate complex – the molecule of the
substrate bound with the enzyme
• Products – the reacted parts of the substrate
Enzyme reaction
Bond
Substrate
1. The substrate,
sucrose consists of
glucose and fructose
bonded together
Active site
Enzyme
2. The substrate
binds with the
enzyme to form
the enzymesubstrate
complex
H2O
3. The binding of the
substrate and enzyme
places stress on the
glucose- fructose bond
and the bond breaks
4. Products are
released, and the
enzyme is free to
bind with other
substrates
Lock and Key Analogy
• In 1894, Emil Fischer postulated that each enzyme
and substrate are specific to each other much like a
lock and key.
• Only the correct key (substrate) will fit into the key
hole (active site) each lock (enzyme)
Factors which affect enzyme
activity
• pH- Enzyme function is best at a pH of 7.4.
If the pH
is to high it will denature the enzyme and will no
longer function
• Temperature – To a certain extent, the higher the
temperature the faster the enzyme works because
the substrates are moving faster. The enzyme will
be denatured and not function anymore
• Inhibitors – Stop enzymes from functioning. There
are two types
Competitive inhibitors which have a similar shape to the
substrate and therefore can “compete” with the
enzyme
• Non-competitive inhibitors which do not bind to the
active site but block the enzyme substrate complex
from forming. They react with portions of the action
site, changing the enzymes shape so it doesn’t function
anymore
•
Athletes and Protein
• Athletes require more protein then non-
athletes
• Strength athletes require 1.8-2 times as
much protein and endurance athletes
require 1.5-1.75 times as much
• Regular exercise stimulates tissue growth
and causes tissue damage, which must be
repaired by additional proteins
• This is what causes athletes to “bulk up”
and why athletes must ingest protein
before and after a work out.
Too much protein
• Weight gain – a lot of protein contains a
high amount of cholesterol and fat from
animals.
• Reduced liver and brain function – when
you eat protein your body produces
ammonia, a toxin that your liver makes
harmless. Eating protein causes your liver
to become overworked allowing ammonia
and other toxins to build up in your body,
which can lead to decline in brain and
nervous system function
Too little protein
• Kwashiorkor – “under nutrition”
under weight, dry
skin, dry fragile hair that may fall out easily. Can
lead to bloated swollen looking stomach
• Muscle Degradation – without the sufficient protein
your body will begin to break down muscles in order
to use the components of the muscle else where
• Compromised Hormone and Immune Function –
Amino acids are required to create different
hormones. Lack of amino acids can lead to
hormone imbalance
• Marasmus – a severe form of malnutrition.
Characterized by a look of skin and bones, and a
loss of energy
Video
• https://www.youtube.com/watch?v=H8WJ2KENlK0