<< Chapter < Page Chapter >> Page >

Many organisms are only able to use one enantiomeric form of certain types of molecules as nutrients and as building blocks to make structures within a cell. Some enantiomeric forms of amino acids have distinctly different tastes and smells when consumed as food. For example, L-aspartame, commonly called aspartame, tastes sweet, whereas D-aspartame is tasteless. Drug enantiomers can have very different pharmacologic affects. For example, the compound methorphan exists as two enantiomers, one of which acts as an antitussive ( dextro methorphan, a cough suppressant), whereas the other acts as an analgesic ( levo methorphan, a drug similar in effect to codeine).

Diagrams showing enantiomers; each diagram has 2 molecules with a dashed line labeled “mirror” in between them. The chemical formula for D and L glucose both have a 6 C chain with a double bonded O at the top carbon. Each of the other carbons has an OH on the opposite side – for example the OH on the second carbon is on the right in D-glucose and on the left in L-glucose. D-alanine and L-alanine both have a 3 carbon chain, but the NH2 group is on opposite sides of the chain in each of these.
Enantiomers are stereoisomers that exhibit chirality. Their chemical structures are nonsuperimposable mirror images of each other. (a) D-glucose and L-glucose are monosaccharides that are enantiomers. (b) The enantiomers D-alanine and L-alanine are enantiomers found in bacterial cell walls and human cells, respectively.

Enantiomers are also called optical isomers because they can rotate the plane of polarized light. Some of the crystals Pasteur observed from wine fermentation rotated light clockwise whereas others rotated the light counterclockwise. Today, we denote enantiomers that rotate polarized light clockwise (+) as d form s, and the mirror image of the same molecule that rotates polarized light counterclockwise (−) as the l form . The d and l labels are derived from the Latin words dexter (on the right) and laevus (on the left), respectively. These two different optical isomers often have very different biological properties and activities. Certain species of molds, yeast, and bacteria, such as Rhizopus , Yarrowia , and Lactobacillus spp., respectively, can only metabolize one type of optical isomer; the opposite isomer is not suitable as a source of nutrients. Another important reason to be aware of optical isomers is the therapeutic use of these types of chemicals for drug treatment, because some microorganisms can only be affected by one specific optical isomer.

  • We say that life is carbon based. What makes carbon so suitable to be part of all the macromolecules of living organisms?

Biologically significant functional groups

In addition to containing carbon atoms, biomolecules also contain functional groups —groups of atoms within molecules that are categorized by their specific chemical composition and the chemical reactions they perform, regardless of the molecule in which the group is found. Some of the most common functional groups are listed in [link] . In the formulas, the symbol R stands for “residue” and represents the remainder of the molecule. R might symbolize just a single hydrogen atom or it may represent a group of many atoms. Notice that some functional groups are relatively simple, consisting of just one or two atoms, while some comprise two of these simpler functional groups. For example, a carbonyl group is a functional group composed of a carbon atom double bonded to an oxygen atom: C=O. It is present in several classes of organic compounds as part of larger functional groups such as ketones, aldehydes, carboxylic acids, and amides. In ketones, the carbonyl is present as an internal group, whereas in aldehydes it is a terminal group.

Questions & Answers

what is the difference between prokaryotic and eukaryotic?
Brian Reply
how many types of cell
Brian Reply
Two PLANT AND ANIMAL CELL
Shafi
actually we have two major types eukaryotic and prokaryotic eukaryotic may me unicellular as yeast or multicellular as plant ,animal, algae,fungi prokaryotic as bacteria
Khaled
hi, what are the most important things i should focus on to passed this class
Mulbah
guys I know is out of topic but I really need help
Mulbah
Hi
Brian
hi, any tips on this subject
Mulbah
you only need to focus on your study and you should expand your time of studying if there is any blockage for you
Alieu
Hi dear any one can splain how it is made Collagen peptide
natural
It's made of many bonds and proteins that are used to block
Lee
what is the evolutionary Trent of butterfly
ANTHONY
the history of cell theory.
Usman Reply
what are the principle of gram staining?
Hussaina
gram positive bacteria have matrix 10% and murein 90% which consists of peptidoglycan about four layers (very thick). gram negative bacteria have matrix 90% and murein 10% which consists of peptidoglycan about 2 layers (thin)
Khaled
so in gram positive bacteria : purple stain is trapped make alcohol can't leach it in gram procedure so appear purple (violet) in gram negative bacteria : purple stain is leached by alcohol and red stain of safranin after leaching give red colour appearance to gram negative.
Khaled
Name 4 Afb positive and negative bacteria?
sujay Reply
e coli staphylococcus streptococcus pseudomomas
Matilda
what invention
MALAMI Reply
?
Teressa
learn about micro bacterium tuberculosis
Dian
What are the conventional methods of microorganism detection?
Anna Reply
What are the convectional methods for microorganism detection
Anna
what is kidney stones. list some food that can heal it . How can kidney stone be cured?
dennis Reply
Are problèms related for crystal.
Abdullahi
is a calculus formed in the kidney
stephen
yes
tanya
eat light foods
Chandrima
just go tjorough bland diet
Chandrima
what are monomers, and is there a section for bacterial metabolism
SAM Reply
who is Aristotle?
soko Reply
Aristotle is the father of Biology.
Margrete
is a father of western philosophy
Kamaluddeen
father of classification of organisms
Williams
This is one of the greatest of the ancient Athenian philosophers
stephen
Sorry Aristotle was father of zoology
Sauri
father of classification of organisms
Williams
father of classification
Joy
Okay father of zoology
Joy
The bacteria that cause plague belong to the genes
Javid Reply
structure and functions of bacterial cell economic environment
Pavi Reply
what is haemaophilus influenzae
GALI Reply
what is the different between eubacteria and archaer bacteria
GALI
what the important of dna
Yunusa Reply
it act as hereditary material, coding for proteins and guide for life processes such as development reproduction etc
khan
Saving information from one generation to another, plus Structurale, fonctional, reproductive role
Ben
It's just structural, functional&
Nandkishor
liver is the largest organ of the body
maryam Reply
Liver is the largest internal organ within the human body but for this question the skin is the largest organ of the human body.
Margrete
Liver is the largest internal organ within the human body but for this question the skin is the largest organ of the human body.
Margrete
differences between prokaryotes and eukaryotes
Taiwo Reply
Eukaryotic cells contain membrane-bound organelles, such as the nucleus, while prokaryotic cells do not.
Margo
hello
usman
margo calvi....its your simple difference
Sadiqur
likely objective questions
Naa
what is largest Organ in the body
Dr
Skin is the largest organ in the body
Yadav
heart is the largest organ of the body
usman
liver is the largest organ in the body
maryam
liver is the largest organ in the body
maryam
skin
Janet
skin
Elyas
bilharzia
Elyas
i need formation
Elyas
liver is the largest organ in the body
maryam
Skin is the largest
Amin
skin
Amin

Get the best Microbiology course in your pocket!





Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

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

Ask