<< Chapter < Page Chapter >> Page >

In triglycerides (fats and oils), long carbon chains known as fatty acids may contain double bonds, which can be in either the cis or trans configuration, illustrated in [link] . Fats with at least one double bond between carbon atoms are unsaturated fats. When some of these bonds are in the cis configuration, the resulting bend in the carbon backbone of the chain means that triglyceride molecules cannot pack tightly, so they remain liquid (oil) at room temperature. On the other hand, triglycerides with trans double bonds (popularly called trans fats), have relatively linear fatty acids that are able to pack tightly together at room temperature and form solid fats. In the human diet, trans fats are linked to an increased risk of cardiovascular disease, so many food manufacturers have reduced or eliminated their use in recent years. In contrast to unsaturated fats, triglycerides without double bonds between carbon atoms are called saturated fats, meaning that they contain all the hydrogen atoms available. Saturated fats are a solid at room temperature and usually of animal origin.

Oleic acid and eliadic acid both consist of a long carbon chain. In oleic acid the chain is kinked due to the presence of a double bond about half way down, while in eliadic acid the chain is straight.
These space-filling models show a cis (oleic acid) and a trans (eliadic acid) fatty acid. Notice the bend in the molecule cause by the cis configuration.

Enantiomers

Enantiomers are molecules that share the same chemical structure and chemical bonds but differ in the three-dimensional placement of atoms so that they are mirror images. As shown in [link] , an amino acid alanine example, the two structures are non-superimposable. In nature, only the L-forms of amino acids are used to make proteins. Some D forms of amino acids are seen in the cell walls of bacteria, but never in their proteins. Similarly, the D-form of glucose is the main product of photosynthesis and the L-form of the molecule is rarely seen in nature.

Molecular models of D-and L-alanine are shown. The two molecules, which contain the same number of carbon, hydrogen, nitrogen atoms, are mirror images of one another.
D-alanine and L-alanine are examples of enantiomers or mirror images. Only the L-forms of amino acids are used to make proteins.

Functional groups

Functional groups are groups of atoms that occur within molecules and confer specific chemical properties to those molecules. They are found along the “carbon backbone” of macromolecules. This carbon backbone is formed by chains and/or rings of carbon atoms with the occasional substitution of an element such as nitrogen or oxygen. Molecules with other elements in their carbon backbone are substituted hydrocarbons .

The functional groups in a macromolecule are usually attached to the carbon backbone at one or several different places along its chain and/or ring structure. Each of the four types of macromolecules—proteins, lipids, carbohydrates, and nucleic acids—has its own characteristic set of functional groups that contributes greatly to its differing chemical properties and its function in living organisms.

A functional group can participate in specific chemical reactions. Some of the important functional groups in biological molecules are shown in [link] ; they include: hydroxyl, methyl, carbonyl, carboxyl, amino, phosphate, and sulfhydryl. These groups play an important role in the formation of molecules like DNA, proteins, carbohydrates, and lipids. Functional groups are usually classified as hydrophobic or hydrophilic depending on their charge or polarity characteristics. An example of a hydrophobic group is the non-polar methane molecule. Among the hydrophilic functional groups is the carboxyl group found in amino acids, some amino acid side chains, and the fatty acids that form triglycerides and phospholipids. This carboxyl group ionizes to release hydrogen ions (H + ) from the COOH group resulting in the negatively charged COO - group; this contributes to the hydrophilic nature of whatever molecule it is found on. Other functional groups, such as the carbonyl group, have a partially negatively charged oxygen atom that may form hydrogen bonds with water molecules, again making the molecule more hydrophilic.

Table shows the structure and properties of different functional groups. Hydroxyl groups, which consist of OH attached to a carbon chain, are polar. Methyl groups, which consist of three hydrogens attached to a carbon chain, are nonpolar. Carbonyl groups, which consist of an oxygen double bonded to a carbon in the middle of a hydrocarbon chain, are polar. Carboxyl groups, which consist of a carbon with a double bonded oxygen and an OH group attached to a carbon chain, are able to ionize, releasing H+ ions into solution. Carboxyl groups are considered acidic. Amino groups, which consist of two hydrogens attached to a nitrogen, are able to accept H+ ions from solution, forming H3+. Amino groups are considered basic. Phosphate groups consist of a phosphorous with one double bonded oxygen and two OH groups. Another oxygen forms a link from the phosphorous to a carbon chain. Both OH groups in phosphorous can lose a H+ ion, and phosphate groups are considered acidic.
The functional groups shown here are found in many different biological molecules.

Hydrogen bonds between functional groups (within the same molecule or between different molecules) are important to the function of many macromolecules and help them to fold properly into and maintain the appropriate shape for functioning. Hydrogen bonds are also involved in various recognition processes, such as DNA complementary base pairing and the binding of an enzyme to its substrate, as illustrated in [link] .

Molecular models show hydrogen bonding between thymine and adenine, and between cytosine and guanine. These four DNA bases are organic molecules containing carbon, nitrogen, oxygen, and hydrogen in complex ring structures. Hydrogen bonds between the bases hold them together.
Hydrogen bonds connect two strands of DNA together to create the double-helix structure.

Section summary

The unique properties of carbon make it a central part of biological molecules. Carbon binds to oxygen, hydrogen, and nitrogen covalently to form the many molecules important for cellular function. Carbon has four electrons in its outermost shell and can form four bonds. Carbon and hydrogen can form hydrocarbon chains or rings. Functional groups are groups of atoms that confer specific properties to hydrocarbon (or substituted hydrocarbon) chains or rings that define their overall chemical characteristics and function.

Art connections

[link] Which of the following statements is false?

  1. Molecules with the formulas CH 3 CH 2 COOH and C 3 H 6 O 2 could be structural isomers.
  2. Molecules must have a double bond to be cis - trans isomers.
  3. To be enantiomers, a molecule must have at least three different atoms or groups connected to a central carbon.
  4. To be enantiomers, a molecule must have at least four different atoms or groups connected to a central carbon.

[link] C

Got questions? Get instant answers now!

Questions & Answers

give me somes of examples.
Manu Reply
give example of what.
Ante
example of what
Elizabeth
what are chromosomes?
Ante
what is Biology
Darkoa
Ecology is the study of
Abdul Reply
Ecology is the study of the interaction of organism in each other and their environment.
Ante
Ecology is the study of the interaction of organism in each other and their environment
Everlove
oh yes!!! exactly
Great
thank much
Ante
what is biome?
Ante
a geographical area with dinstic species
Francis
thanks much it very helpful
Ante
my pleasure
Francis
characteristics of living things
Jane Reply
excretion, movement, sensitivity, reproduction,growth, respiration,nutrition
Estel
what are there function
Ante
what are their function
Ante
what is the two type of reproduction?
Ante
sexual reproduction and asexual reproduction
Abdul
what are their function
Manu
Hi
Olufunmilokun
What is light independent reaction
Benjamin Reply
correct word or phrase. ______A____ uses carbon dioxide and _____B______ to make sugar during______C______. _____D______ traps light energy during this process. *
Andrea Reply
A_plant ,B_water,C_photosynthesis,D_chlorophyll
Abdul
Plant,sunlight,photosynthesis
Olufunmilokun
by which of the following feature c3 and c4 plant similar A .enzyme used to fix carbon dioxide B.cell where calvin cycle takes place C.cell where carbon dioxide fixation takes place
Kaleab Reply
correct word or phrase. ______A____ uses carbon dioxide and _____B______ to make sugar during______C______. _____D______ traps light energy during this process. *
Andrea
what is biology ?
Bizone Reply
study of organisms
Aurelia
what is link
Lamina Reply
is carbon an organism that matter?
DKP Reply
what is buttress root?
Dora Reply
Buttress root are wide large root
Iyabo
Buttress root/roots are thick roots that emerge out form the base of a large canopy
Musoke
From the base of a large canopy
Musoke
What is biology
Jiboh Reply
Biology is the study of structure and growth of living things and organisms within their biography
Musoke
compare the mechanism of gaseous exchange in an insect and mammal
World Reply
what are the characteristic of livingthing
Joy Reply
Movement Respiration Nutrition Irritability or sensitivity Growth Excretion Reproduction Adaptation Competition Death or Life Span
Emmanuel
Respiration Irritability Movement Excretion Nutrition Growth Reproduction
Amponsah
movement respiration nutrition irritability growth excretion reproduction death
Elizabeth
what is the function of medulla oblongata
mbalenhle Reply
what is the strongest bone in the human body
Chionye
what is biology
Dauda Reply
is a branch of science which deals with the study of living thing
sheka
thanks
Dauda
Biology is got from two main words: bios: means life and Logos: means knowledge therefore, biology is a branch of science that deals with knowledge, life and functioning of living things.
Musoke
what are the characteristics of organism
Seldam
Responds to stimuli
Musoke
Biology is an aspect of science that deals with the. study of living organisms
Amponsah

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




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