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The five bases that are found in nucleotides are often represented by their initial letter: adenine, A; guanine, G; cytosine, C; thymine, T; and uracil, U. You are not required to memorize the structures of these bases, but you must know how each one bonds to the sugar unit in a nucleotide.
The Learning Objective of this Module is to identify the different molecules that combine to form nucleotides. The repeating, or monomer, units that are linked together to form nucleic acids are known as nucleotides. Nucleotides can be further broken down to phosphoric acid H 3 PO 4 , a pentose sugar a sugar with five carbon atoms , and a nitrogenous base a base containing nitrogen atoms. If the pentose sugar is ribose, the nucleotide is more specifically referred to as a ribonucleotide , and the resulting nucleic acid is ribonucleic acid RNA.
If the sugar is 2-deoxyribose, the nucleotide is a deoxyribonucleotide , and the nucleic acid is DNA. The nitrogenous bases found in nucleotides are classified as pyrimidines or purines.
Pyrimidines are heterocyclic amines with two nitrogen atoms in a six-member ring and include uracil, thymine, and cytosine. Purines are heterocyclic amines consisting of a pyrimidine ring fused to a five-member ring with two nitrogen atoms.
In the formation of this bond, a molecule of water is removed. Table The numbering convention is that primed numbers designate the atoms of the pentose ring, and unprimed numbers designate the atoms of the purine or pyrimidine ring. Apart from being the monomer units of DNA and RNA, the nucleotides and some of their derivatives have other functions as well.
Nucleotides are joined together through the phosphate group of one nucleotide connecting in an ester linkage to the OH group on the third carbon atom of the sugar unit of a second nucleotide. This unit joins to a third nucleotide, and the process is repeated to produce a long nucleic acid chain Figure The purine and pyrimidine bases branch off this backbone. Each phosphate group has one acidic hydrogen atom that is ionized at physiological pH. This is why these compounds are known as nucleic acids.
Like proteins, nucleic acids have a primary structure that is defined as the sequence of their nucleotides. Unlike proteins, which have 20 different kinds of amino acids, there are only 4 different kinds of nucleotides in nucleic acids. For amino acid sequences in proteins, the convention is to write the amino acids in order starting with the N-terminal amino acid. In writing nucleotide sequences for nucleic acids, the convention is to write the nucleotides usually using the one-letter abbreviations for the bases, shown in Figure For DNA, a lowercase d is often written in front of the sequence to indicate that the monomers are deoxyribonucleotides.
The sequence of nucleotides in the DNA segment shown in Figure For each structure, circle the sugar unit and identify the nucleotide as a ribonucleotide or a deoxyribonucleotide.
Steven Farmer Sonoma State University. Objectives After completing this section, you should be able to outline the relationship between nucleic acids, nucleotides and nucleosides. Key Terms Make certain that you can define, and use in context, the key terms below. Study Notes The five bases that are found in nucleotides are often represented by their initial letter: adenine, A; guanine, G; cytosine, C; thymine, T; and uracil, U.
To fulfill Objective 6, you should be able to reproduce the figure below. Primary Structure of Nucleic Acids Nucleotides are joined together through the phosphate group of one nucleotide connecting in an ester linkage to the OH group on the third carbon atom of the sugar unit of a second nucleotide.
Note Each phosphate group has one acidic hydrogen atom that is ionized at physiological pH. Concept Review Exercises Identify the three molecules needed to form the nucleotides in each nucleic acid.
Classify each compound as a pentose sugar, a purine, or a pyrimidine. Answers nitrogenous base adenine, guanine, cytosine, and thymine , 2-deoxyribose, and H 3 PO 4 nitrogenous base adenine, guanine, cytosine, and uracil , ribose, and H 3 PO 4. Key Takeaways Nucleotides are composed of phosphoric acid, a pentose sugar ribose or deoxyribose , and a nitrogen-containing base adenine, cytosine, guanine, thymine, or uracil.
Ribonucleotides contain ribose, while deoxyribonucleotides contain deoxyribose. Exercises What is the sugar unit in each nucleic acid?
Identify the major nitrogenous bases in each nucleic acid. For each structure, circle the nitrogenous base and identify it as a purine or pyrimidine.
Answers ribose deoxyribose. Contributors and Attributions Dr.
If your institution subscribes to this resource, and you don't have a MyAccess Profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus. Please consult the latest official manual style if you have any questions regarding the format accuracy. Nucleosides and nucleotides are the fourth and final major group of biochemical molecules and are essential for numerous biological functions in humans, including maintaining and transferring genetic information, playing a major role in energy storage, and acting as signaling molecules. These molecules can be divided into two major families—purines, which include adenosine and guanine, and pyrimidines, which include cytosine, thymidine, and uracil. The unique structures and interactions of these molecules serve as the building blocks of RNA and DNA molecules and allow fundamental processes of gene replication and protein synthesis to occur.
Clipping is a handy way to collect important slides you want to go back to later. Nucleotides that compose DNA are called deoxyribonucleotides. Learn new and interesting things. Get ideas for … A level biology new specification for
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The nucleic acid backbone then is asequence of sugar-phosphate groups, whichdiffer only in the sequence of bases.Reply