<< Chapter < Page Chapter >> Page >
The formation of a peptide bond between two amino acids is shown. When the peptide bond forms, the carbon from the carbonyl group becomes attached to the nitrogen from the amino group. The OH from the carboxyl group and an H from the amino group form a molecule of water.
Peptide bond formation is a dehydration synthesis reaction. The carboxyl group of one amino acid is linked to the amino group of the incoming amino acid. In the process, a molecule of water is released.

The products formed by such linkages are called peptides. As more amino acids join to this growing chain, the resulting chain is known as a polypeptide. Each polypeptide has a free amino group at one end. This end is called the N terminal, or the amino terminal, and the other end has a free carboxyl group, also known as the C or carboxyl terminal. 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, often have bound non-peptide prosthetic groups, have a distinct shape, and have a unique function. After protein synthesis (translation), most proteins are modified. These are known as post-translational modifications. They may undergo cleavage, phosphorylation, or may require the addition of other chemical groups. Only after these modifications is the protein completely functional.

Click through the steps of protein synthesis in this interactive tutorial .

Evolution connection

The evolutionary significance of cytochrome c

Cytochrome c is an important component of the electron transport chain, a part of cellular respiration, and it is normally found in the cellular organelle, the mitochondrion. This protein has a heme prosthetic group, and the central ion of the heme gets alternately reduced and oxidized during electron transfer. Because this essential protein’s role in producing cellular energy is crucial, it has changed very little over millions of years. Protein sequencing has shown that there is a considerable amount of cytochrome c amino acid sequence homology among different species; in other words, evolutionary kinship can be assessed by measuring the similarities or differences among various species’ DNA or protein sequences.

Scientists have determined that human cytochrome c contains 104 amino acids. For each cytochrome c molecule from different organisms that has been sequenced to date, 37 of these amino acids appear in the same position in all samples of cytochrome c. This indicates that there may have been a common ancestor. On comparing the human and chimpanzee protein sequences, no sequence difference was found. When human and rhesus monkey sequences were compared, the single difference found was in one amino acid. In another comparison, human to yeast sequencing shows a difference in the 44th position.

Protein structure

As discussed earlier, the shape of a protein is critical to its function. For example, an enzyme can bind to a specific substrate at a site known as the active site. If this active site is altered because of local changes or changes in overall protein structure, the enzyme may be unable to bind to the substrate. 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.

Questions & Answers

Hello how are you every body
Sitali Reply
join the conversation
Sitali
l am fine every body
Memiru
I'm very fine_hopefully everyone is fine
Rorisang
what is meant by submicroscopic?
anji Reply
what is anabolic and catabolic
Jonathan
hi
Alpha
hi berther
Memiru
hallo
Memiru
what is the meaning of biology
Dorathy Reply
biology is scientific study of living things
GUYO
what is chromosomes?
Mabiya Reply
it is a cell structure that contains DNA histones protein and other structural proteins
Ekechi
what is DNA
Kashah
what is liver
Hassan Reply
liver is an organ in the body that meterbolise nutrients and produce bile.
Ekechi
what is the function of granum?
Gulfam
what is the faction of liver cancer
Kashah
What is biology
Eric Reply
Biology is you
muayad
Biology is the natural science that studies life and living organisms, including their physical structure, chemical processes, molecular interactions, physiological mechanisms, development and. evolution
Suzette
biology is the study of living things and none living things
Ekechi
study of living organisms
anji
The mamalian endoskeleton has 206 bones
kaazim Reply
hii
Hannah
hi
Suzette
how you
Hannah
good thanks
Suzette
have you done the actual course?
Suzette
How many bones do human body have?
moses Reply
I don't know please help me
Kisito
206
Waneh
206
Moses
206
anji
what are these geneti materials
ONELIA Reply
Name five parts of female reproductive system and state the function of each part
Angel Reply
What is biology
Angel
What is biology
Angel
biology is the study of all living organisms
ketchem
Ok
Angel
Name five parts of female reproductive system and state the function of each part
Angel
What is the meaning of respiration
Idriss Reply
the act or process of breathing .
Suzette
the process is very long as I know
Idriss
do you want more details ?
Suzette
yes offcourse
Smiso
what does the term diploid and haploid mean?
ONELIA
what is virgina
Shebas Reply
A female reproductive organs
Julius
fuvu LA binadam linamifupa mingapi?
Hamis Reply
explain dicot n monocot plant
Henry Reply
Di= 2cotiledon mono=cotiledon
muayad
Mono = 1 cotiledon
muayad
what is virginia
Shebas
A Virginia is a part of a female ,the passage of a child during child birth, receiver of the penis and the passage of menstral flow
Idriss
what is biology
Hassan Reply
what is liver
Hassan
Biology is the study of living organisms
Gifty
is the study of life of living organisms
Chansa
study all about organisms like their reproduction, evolution , behaviour Physiology, etc
Ubaid
this is what we call "life"@
Chansa
is the study of living organisms on earth
okubasu
It is the study of living organism
Idriss
Biology is the study of all living organisms
ketchem
what is copulation
ketchem

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play




Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Biology' conversation and receive update notifications?

Ask