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Steroids

Unlike the phospholipids and fats discussed earlier, steroids have a ring structure. Although they do not resemble other lipids, they are grouped with them because they are also hydrophobic. All steroids have four, linked carbon rings and several of them, like cholesterol, have a short tail.

Cholesterol is a steroid. Cholesterol is mainly synthesized in the liver and is the precursor of many steroid hormones, such as testosterone and estradiol. It is also the precursor of vitamins E and K. Cholesterol is the precursor of bile salts, which help in the breakdown of fats and their subsequent absorption by cells. Although cholesterol is often spoken of in negative terms, it is necessary for the proper functioning of the body. It is a key component of the plasma membranes of animal cells.

Concept in action

For an additional perspective on lipids, explore “Biomolecules: The Lipids” through this interactive animation .

Proteins

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 different 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.

The functions of proteins are very diverse because there are 20 different chemically distinct amino acids that form long chains, and the amino acids can be in any order. For example, proteins can function as enzymes or hormones. Enzymes , which are produced by living cells, are catalysts in biochemical reactions (like digestion) and are usually proteins. Catalysts speed up chemical reactions by lowering the amount of energy required to start them. Each enzyme is specific for the substrate (a reactant that binds to an enzyme) upon which it acts. Enzymes can function to break molecular bonds, to rearrange bonds, or to form new bonds. An example of an enzyme is salivary amylase, which breaks down amylose, a component of starch.

Hormones are chemical signaling molecules, usually proteins or steroids, secreted by an endocrine gland or group of 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 maintains blood glucose levels.

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. Changes in temperature, pH, and exposure to chemicals may lead to permanent changes in the shape of the protein, leading to a loss of function or denaturation    (to be discussed in more detail later). All proteins are made up of different arrangements of the same 20 kinds of amino acids.

Questions & Answers

In the digestive system,what are nucleotides and what is their use
Leo Reply
what is the difference between kidney and liver
Raphael
what's an isomer
marybertiny Reply
is a chemical species with the same number and types of atoms as another chemical species but with distinct properties because rhe atoms are arranged into different chemical structures.
yaad
How are they important to anmals
Leo
immune system protect body from harmful foreign cells
Hira Reply
that's right some time when bacteria attached the body the immune system product
abdala
what is function of the body
Sarat Reply
Body funtion. Our bodies consist of a number of biological systems that carry out specific functions necessary for everyday living. The job of the circulatory system is to move blood, nutrients, oxygen, carbon dioxide, and hormones, around the body. It consists of the heart, blood, blood vessels,art
Sayed
what's the function of the lymphatic system
Samuel
how long does it take for food process to reach the deudenum
Braveson
how does it takes for food to digested
Kelliann
how long does it takes for food to digested
Kelliann
what are tissue
Nkeng Reply
what are the difference type of connective tissue
Nkeng
Types of connective tissue 1. Loose connective tissue: a.Areolar connective tissue b.Adipose connective tissue 2. Dense (fibrous) connective tissue: I. Compact tissue a.White fibrous tissue ( tendon and sheath) b.Yellow elastic tissue (Ligament) II. Supporting connective tissue: types- 1. Cartilag
iti
2. Bone III. Fluid or liquid connective tissue: Blood lymph
iti
What is cytoplasm
Uyi Reply
what is cytoplasm
Morgan
a cytoplasm is a fluid found inside the cell membrane which contains dissolved minerals e.t.c.
Fortune
ok
Morgan
why is the the mitochondria known as the power house?
Fortune
The mitochondria is involved in releasing energy from food..this process is known as cellular respiration.
Sherice
ok
Fortune
what is Deoxyribonucleic Acid (DNA)?
Jackson
is a molecule composed of two chains.
Fortune
is a molecule composed of two chains that coil around each other to form a double helix carrying the genetics instructions used in growth,development e.t.c.
Fortune
Thanks
Jackson
structur of the heart
Munyah Reply
hi
Unimke
Hello
Mariam
miss Mariam u are welcome
Emmanuel
hello
wana
hii
Dein-aboh
hi
Wani
how
Renzo
hello every one
BOBO
hello
iti
hello
Hilmi
hello
Eshiemoghie
hi
Vaishnavi
what is mutation?
Oliver
Hi to everybody
Hussein
essay for photosynthesis
NiCho Reply
essay of the human body
NiCho
how do female menstrual uterus prepare for fertilisation?
Jackson
what is blood pressure
Sid Reply
to my understanding blood pressure is where u are shock with something emergency I think that can also course blood pressure
Badu
what is the meaning of extended family
Shellyann Reply
extended family is two are more nuclear family living together under one roof
Nordalee
what is genetic engineering
Ebot Reply
good day please what is a cell?
Colota Reply
cell is the basic unit of all living things/organism
Hassan
differenciate b/w cilia and flagellum
Abshira
Cilia: 1. They are smaller in number. 2. Cilia usually occur throughout or major part of the surface of a cell. 3. They beat oar like and in a co-ordinated rhythm 4. Cilia help in locomotion, feeding, circulation, etc.. 5. Example: Paramecium
iti
Flagella: 1. They are larger in size. ADVERTISEMENTS: 2. Flagella are commonly found at one end of the cell. 3. The flagella beat whip-like and independently. 4. Flagella help in locomotion. 5. Example: Euglena
iti
smallest structural and functional unit of an organism!
zidane
cell is the basic unit of all living things
Lukman
A cell is a basic unit of life
Badu
please I want to know the meaning of Tissues
Badu
hellooo here
Ebot
h2
Oliver
meaning of dispesing
Oliver
thnk u iti
Abshira
tissue is a group of identical cells having common origin
iti
what is the word? dispensing or dispersing...check the spelling of the word.
iti
dispersing
Oliver
Smaller in size not in number
Md
They are small in size and more in number
Md
Not identical but similar
Md
 cell is the smallest unit of life. Cellsare often called the "building blocks of life". The study of cells is called cellbiology. Cells consist of cytoplasm enclosed within a membrane, which contains many biomolecules such as proteins and nucleic acids.
Harun
hi
Vaishnavi
how are u doing
Emmanuel
this thing I don't know whether is an instruments use to measure pressure Sphygmomanometer is it true or not because in my formal school that's my master told me
Badu
dispersing means distribution or spreading
iti
sphygmomanometer is used for measuring blood pressure
iti
thanks
Oliver
mention the functions of mitochondria?
Oliver
mitochondria is the powerhouse of cell. it generates and stores energy in the form of ATP molecules in its oxysomes. it has its own DNA so its capable of self replicating and hence also called as semi autonomous organelle
iti
welcome
iti
explain briefly anatomy
Oliver
anatomy is thr study of internal structures and their organization as well as functions of living organisms
iti
OK thanky
Oliver
Yes
Hilmi
Good
Moses
welcome
iti
differenciate b/w red blood cell and whight blood cell
BOBO
d
Wani
what is homeostasis
alex Reply
the ability of an organism to maintain stable internal environment, even when the external environment changes
Bee
what's the function of the hypothalamus
Agyekum
The hypothalamus is apart of the lower middle brain that tells the pituitary glands when to release hormones
taehyunggg
what is homeostasis
Edward Reply
constant maintenance of internal body temperature
Agyekum
What is the function of the Pituitary Gland?
WeNdlovu
how can homeostasis be maintained?
alex
pituitary gland also known as the master gland secretes hormones which triggers other gland to secretes their hormones
Agyekum
what's the full meaning of DNA and RNA
Deborah Reply
DNA is Deoxyribonucleic acid and RNA means Ribonucleic acid
Christian

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Source:  OpenStax, Human biology. OpenStax CNX. Dec 01, 2015 Download for free at http://legacy.cnx.org/content/col11903/1.3
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