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Amino acids are the monomers that make up proteins. Each amino acid has the same fundamental structure, which consists of a central carbon atom bonded to an amino group (–NH 2 ), a carboxyl group (–COOH), and a hydrogen atom. Every amino acid also has another variable atom or group of atoms bonded to the central carbon atom known as the R group. The R group is the only difference in structure between the 20 amino acids; otherwise, the amino acids are identical ( [link] ).

The fundamental molecular structure of an amino acid is shown. Also shown are the molecular structures of alanine, valine, lysine, and aspartic acid, which vary only in the structure of the R group
Amino acids are made up of a central carbon bonded to an amino group (–NH 2 ), a carboxyl group (–COOH), and a hydrogen atom. The central carbon’s fourth bond varies among the different amino acids, as seen in these examples of alanine, valine, lysine, and aspartic acid.

The chemical nature of the R group determines the chemical nature of the amino acid within its protein (that is, whether it is acidic, basic, polar, or nonpolar).

The sequence and number of amino acids ultimately determine a protein’s shape, size, and function. Each amino acid is attached to another amino acid by a covalent bond, known as a peptide bond, which is formed by a dehydration reaction. The carboxyl group of one amino acid and the amino group of a second amino acid combine, releasing a water molecule. The resulting bond is the peptide bond.

The products formed by such a linkage are called polypeptides. While the terms polypeptide and protein are sometimes used interchangeably, a polypeptide    is technically a polymer of amino acids, whereas the term protein is used for a polypeptide or polypeptides that have combined together, have a distinct shape, and have a unique function.

Protein structure

As discussed earlier, the shape of a protein is critical to its function. To understand how the protein gets its final shape or conformation, we need to understand the four levels of protein structure: primary, secondary, tertiary, and quaternary ( [link] ).

The unique sequence and number of amino acids in a polypeptide chain is its primary structure. The unique sequence for every protein is ultimately determined by the gene (i.e. a section of DNA) that encodes (i.e. has the information to make) the protein. Any change in the gene sequence may lead to a different amino acid being added to the polypeptide chain, causing a change in protein structure and function. In sickle cell anemia, the hemoglobin β chain has a single amino acid substitution, causing a change in both the structure and function of the protein. What is most remarkable to consider is that a hemoglobin molecule is made up of two alpha chains and two beta chains that each consist of about 150 amino acids. The molecule, therefore, has about 600 amino acids. The structural difference between a normal hemoglobin molecule and a sickle cell molecule—that dramatically decreases life expectancy in the affected individuals—is a single amino acid of the 600.

Because of this change of one amino acid in the chain, the normally biconcave, or disc-shaped, red blood cells assume a crescent or “sickle” shape, which clogs arteries. This can lead to a myriad of serious health problems, such as breathlessness, dizziness, headaches, and abdominal pain for those who have this disease.

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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