<< Chapter < Page Chapter >> Page >
By the end of this section, you will be able to:
  • Describe the structures of DNA and RNA
  • Describe how eukaryotic DNA is arranged in the cell

In the 1950s, Francis Crick and James Watson worked together at the University of Cambridge, England, to determine the structure of DNA. Other scientists, such as Linus Pauling and Maurice Wilkins, were also actively exploring this field. Pauling had discovered the secondary structure of proteins using X-ray crystallography. X-ray crystallography is a method for investigating molecular structure by observing the patterns formed by X-rays shot through a crystal of the substance. The patterns give important information about the structure of the molecule of interest. In Wilkins’ lab, researcher Rosalind Franklin was using X-ray crystallography to understand the structure of DNA. Watson and Crick were able to piece together the puzzle of the DNA molecule using Franklin's data ( [link] ). Watson and Crick also had key pieces of information available from other researchers such as Chargaff’s rules. Chargaff had shown that of the four kinds of monomers (nucleotides) present in a DNA molecule, two types were always present in equal amounts and the remaining two types were also always present in equal amounts. This meant they were always paired in some way. In 1962, James Watson, Francis Crick, and Maurice Wilkins were awarded the Nobel Prize in Medicine for their work in determining the structure of DNA.

Photo in part A shows James Watson, Francis Crick, and Maclyn McCarty. The x-ray diffraction pattern in part b is symmetrical, with dots in an x-shape.
Pioneering scientists (a) James Watson and Francis Crick are pictured here with American geneticist Maclyn McCarty. Scientist Rosalind Franklin discovered (b) the X-ray diffraction pattern of DNA, which helped to elucidate its double helix structure. (credit a: modification of work by Marjorie McCarty; b: modification of work by NIH)

Now let’s consider the structure of the two types of nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). The building blocks of DNA are nucleotides, which are made up of three parts: a deoxyribose    (a 5-carbon sugar with the carbons designated as 1', 2', 3', 4' and 5'), a phosphate group    attached to the 5'carbon, and a nitrogenous base    attached to the 1'carbon( [link] ). There are four types of nitrogenous bases in DNA. Adenine (A) and guanine (G) are double-ringed purines, and cytosine (C) and thymine (T) are smaller, single-ringed pyrimidines. The nucleotide is named according to the nitrogenous base it contains.

Illustration shows structure of a nucleotide, which is made up of a deoxyribose sugar with a nitrogenous base attached at the 1' position and a phosphate group attached at the 5' position. There are two kinds of nitrogenous bases: pyrimidines, which have one six-membered ring, and purines, which have a six-membered ring fused to a five-membered ring. Cytosine and thymine are pyrimidines, and adenine and guanine are purines.
(a) Each DNA nucleotide is made up of a sugar, a phosphate group, and a base. Four of the five carbon atoms in the sugar are not shown to simplify the diagram; each point on the ring is where a carbon (1' to 4') would be would be located; the position of the 5' carbon is above the ring at the point adjacent to an oxygen of the phosphate group. (b) Cytosine and thymine are pyrimidines. Guanine and adenine are purines. Note: As the 2' carbon is attached to an -OH group, the sugar shown is actually ribose, not deoxyribose as intended.

The phosphate group of one nucleotide bonds covalently with the sugar molecule of the next nucleotide, and so on, forming a long polymer of nucleotide monomers. The sugar–phosphate groups line up in a “backbone” for each single strand of DNA, and the nucleotide bases stick out from this backbone. The carbon atoms of the five-carbon sugar are numbered clockwise from the oxygen as 1', 2', 3', 4', and 5' (1' is read as “one prime”). The phosphate group is attached to the 5' carbon of one nucleotide and the 3' carbon of the next nucleotide. In its natural state, each DNA molecule is actually composed of two single strands held together along their length with hydrogen bonds between the bases.

Questions & Answers

atom, molecules, organelle, cell, tissue, organ, organ system
Cheila Reply
sub atom atom molecular molecules and cells.
Advertus
cells structural level.
Advertus
what is microorganisms I am a laboratory student.
Advertus
explain why is it that old peoples as from the age of 60 usually have eye problems?
Kenn Reply
most old people suffere eye problems.because of short sight where individuals with this kind of problems see only near objects clearly but not distance objects, this is cause by elongated eyeball so light from distance is focus infront the retina so the image on the retina is blurred .
Munyah
plasma DNA cytoplasm Ribosome
Pearl Reply
cell, tissue,organ, organ systems,organism
Pearl Reply
cell is the build block of Life
Pearl
also a smallest unit of life
Frankline
sure..
Pearl
consistsof cytoplsm enclosed with in a membrane which contains many biomolecules such as proteins and nucleic acids
Frankline
differences in the effects of infection by HIV and influenza A virus on host genetic variability.
Yo Reply
i dont know
Ubah
hiv is direct contact of blood or body fluid and if not treated can break down the immune system faster and lead to acids with complications of pneumonia skin infections inflammation of the brain etc.while influenza A is a air borne virus which can cause the common cold pain fever and can be cured
Maureen
A.I.D.S
Maureen
suggest bioingormatics research article plz
peermehirali
what makes the heart to pumps blood?
Jamer Reply
sa node
Ubah
i do think its the nerve tranmission to the brain
Frankline
The contracting and relaxing of the atria and vertricles but the electrical system of the heart is what makes this possible.
keynia
yes which is called autorhymicity
Maureen
adrenoline action in brains
Frankline Reply
please describe the human heart brefly
Shah Reply
the size of the heart is like a fist. it has four chambers. the left and right upper atrium which push blood in the lower left and right ventricles which in turns pump blood to the lungs or the rest of the body.
Maureen
how do u prove it
Frankline
Maureen is correct ,
Davis
right
Kenn
right
Ubah
hi
horyaal
mxaa lahayaa
horyaal
What is housing?
Baldwin Reply
is where located you
Ubah
Hi, my name is Syedul Mostafa from Bangladesh Refugees camp. I would like to study under your.
Mostafa Reply
what is Endocytosis
Alice Reply
Endocytosis is the process where by organism lives inside it host and feed on it
Aboagye
cell
Mostafa
Endocytosis is the process where by substances are taken in to the cell of an organism
Abena
the taking in of matter by a living cell by invagination of its membrane to form a vacuole.
Amber
Exocytosis... is the durable, energy-consuming process by which a cell directs the contents of secretory vesicles out of the cell membrane and into the extracellular space. Endocytosis is an energy-using process by which cells absorb molecules (such as proteins) by engulfing them.
Amber
There are three types of endocytosis: phagocytosis, pinocytosis, and receptor-mediated endocytosis. In phagocytosis or “cellular eating,” the cell's plasma membrane surrounds a macromolecule or even an entire cell from the extracellular environment and buds off to form a food vacuole or phagosome.
Amber
what are hormones
Abena
what the meaning of adenosine triphosphate
Alice Reply
what the full meaning of ADP
Alice
ATP as simply called is substance which provide energy during active transport
Aboagye
what is biology
Alice Reply
biology simply means the study of life
Aboagye
pls HV u get it
Aboagye
what is the cardiovascular disease
Kami Reply
heart disease
Ashley
heart disease
Aboagye
kidney failure
John
heart failure
John
what is the largest cell
Aboagye Reply
tanx wae
Aboagye
what is the name of the largest virus
Aboagye
oohh
Rihan
this is in female body which have ovum which is without fertilization if ovum is fertilize then it is called egg
Abdullahjavaid
Hi
Sanjay
Am new
Sanjay
what is cell division
Kami
in female lagest cell in overy cell
Kami

Get the best Human biology course in your pocket!





Source:  OpenStax, Human biology. OpenStax CNX. Dec 01, 2015 Download for free at http://legacy.cnx.org/content/col11903/1.3
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

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

Ask