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By the end of this section, you will be able to:
  • Describe the functions proteins perform in the cell and in tissues
  • Discuss the relationship between amino acids and proteins
  • Explain the four levels of protein organization
  • Describe the ways in which protein shape and function are linked

Proteins are one of the most abundant organic molecules in living systems and have the most diverse range of functions of all macromolecules. Proteins may be structural, regulatory, contractile, or protective; they may serve in transport, storage, or membranes; or they may be toxins or enzymes. Each cell in a living system may contain thousands of proteins, each with a unique function. Their structures, like their functions, vary greatly. They are all, however, polymers of amino acids, arranged in a linear sequence.

Types and functions of proteins

Enzymes , which are produced by living cells, are catalysts in biochemical reactions (like digestion) and are usually complex or conjugated proteins. Each enzyme is specific for the substrate (a reactant that binds to an enzyme) it acts on. The enzyme may help in breakdown, rearrangement, or synthesis reactions. Enzymes that break down their substrates are called catabolic enzymes, enzymes that build more complex molecules from their substrates are called anabolic enzymes, and enzymes that affect the rate of reaction are called catalytic enzymes. It should be noted that all enzymes increase the rate of reaction and, therefore, are considered to be organic catalysts. An example of an enzyme is salivary amylase, which hydrolyzes its substrate amylose, a component of starch.

Hormones are chemical-signaling molecules, usually small proteins or steroids, secreted by endocrine cells that act to control or regulate specific physiological processes, including growth, development, metabolism, and reproduction. For example, insulin is a protein hormone that helps to regulate the blood glucose level. The primary types and functions of proteins are listed in [link] .

Protein Types and Functions
Type Examples Functions
Digestive Enzymes Amylase, lipase, pepsin, trypsin Help in digestion of food by catabolizing nutrients into monomeric units
Transport Hemoglobin, albumin Carry substances in the blood or lymph throughout the body
Structural Actin, tubulin, keratin Construct different structures, like the cytoskeleton
Hormones Insulin, thyroxine Coordinate the activity of different body systems
Defense Immunoglobulins Protect the body from foreign pathogens
Contractile Actin, myosin Effect muscle contraction
Storage Legume storage proteins, egg white (albumin) Provide nourishment in early development of the embryo and the seedling

Proteins have different shapes and molecular weights; some proteins are globular in shape whereas others are fibrous in nature. For example, hemoglobin is a globular protein, but collagen, found in our skin, is a fibrous protein. Protein shape is critical to its function, and this shape is maintained by many different types of chemical bonds. Changes in temperature, pH, and exposure to chemicals may lead to permanent changes in the shape of the protein, leading to loss of function, known as denaturation    . All proteins are made up of different arrangements of the same 20 types of amino acids.

Questions & Answers

what is the cause of a country's population
Destiny Reply
what is producer surplus
Destiny Reply
is the excess earns btn wat a producer was willing to charge for e commodity and wat actually receives after selling it
OK good
what is supply curve
Destiny Reply
are curve that do not obey the law of supply eg aren't +ve
half of 1%
as in what do u mean by that
it simply shows the quantity of goods that a film is willing to supply at each price of a commodity
OK what is the law of supply as u said
It is the indifference curve that indicates the aggregate responsiveness of supply to the price of a commodity, and sometimes its demand of that same commodity.
pls explain how indifference curve connects to the aggregate responsiveness of supply to the price of a commodity
law of supply according to me states that wen thea z higher price of commodity, the higher will be the supply and lower the supply will be for a commodity other factors remain constant
Joshua be clear to your QN plizzz
pls read Gh's comment and break down for me
may be he can explain more because am am also not getting what he was meaning in that statement
plizzz GH explain to us
When demand and supply intersection
then it z called what
can I learning what is meaning off economics
can you tall me what is meaning
what is consumers surplus
Destiny Reply
is a difference btn consumers planned expenditure and actual experience on the commodity
OK good
What exactly are factors that affects Demand and Supply?
Chandrapaul Reply
demand factors price o commodity size o population level o advertising season 4 commodity testes and preferences price o other related commodity level o consumers income government policy on taxation
supply factors general price level natural factor level o taxation technology political climate cost o production number o producers aggregate demand working conditions
yea___ Demographical psychographical geographical factors also account for determination of demand and supply
definition of economics
Emmanuel Reply
economics means to manage the limited resources one has in order to maximize satisfaction.
Economic is a science which study of human behavior as a relationship between and scare means which have alternative uses"
what is price elasticity of supply
Destiny Reply
What is the law of demand and supply
This is when there is a greater percentage change in the supply of commodities as per the percentage change in price. More producers tend to supply more when there is a higher change in the price of commodities and vice versa when price drops.
this seems to explain making decisions on the margins very clearly
what are the importance of studying Economics ?
Amoako Reply
to relate economic principles to the problems o development. exposes students to e future. acquire knowledge. etc ....
it teaches how to make choice and decisions in our homes and every across the nation
what is price elasticity of supply
five definition of economic s
what is monopoly
Baku Reply
is a structure where one seller of a commodity has no close substitute with very many buyers
a market structure where a particular good has no close substitutes
examples railways
is one man business where there is no competetor/competetion and vice versa
what is income elasticity of demand.
kwagala Reply
percentage change in quantity demanded/percentage change in income
or is the measure of degree of responsiveness o quality demanded o the commodity to change in the income of consumer
percentage change in quantity ÷ percentage change in income
it the percentage change in quantity over percentage in surply
the percentage change in quantity over percentage change in income at the end of the day's work done
what is medium
Chinedu Reply
what is medium in terms of economics
as u mean medium of exchange or just as a word
Your question is not clear @Chinedu. In economics medium is often used in relation to time e.g medium term. So you need to be more specific on which medium you mean. Otherwise it "medium" means what it means everywhere else.
what is medium of exchange
What is the difference between inferior goods and complementary goods
Bernard Reply
inferior goods are goods whose demand reduces as consumers income increases
while complementary goods are goods which are jointly demand
Wow thanks
you are welcome
define the term derived demand
rivan Reply
anyone to help with QN
situation in which a product is acquired not for it's sake but to help in the production of other goods. for example we say labour has a derived demand becos labour services is required to help in the production of other goods and services.
The Market equilibrium quantity is___ tons of bolts, the socailly optimal quantity of bolt production is ____ tons
Jackie Reply
please what are the key principles of Economics?
Difference between extinct and extici spicies
Amanpreet Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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While the American heart association suggests that meditation might be used in conjunction with more traditional treatments as a way to manage hypertension
Beverly Reply
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Source:  OpenStax, General biology i lecture. OpenStax CNX. Aug 25, 2015 Download for free at https://legacy.cnx.org/content/col11869/1.1
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