2.6 RNA/DNA Structure Flashcards
What are nucleic acids?
Nucleic acids are the genetic material of the cell
What are nucleic acids composed of?
are composed of recurring monomeric units called nucleotides
What is each nucleotide composed of? (3)
5-carbon pentose sugar (pentagon) Phosphate group (circle) Nitrogenous base (rectangle)
What is the central molecule of a nucleotide and what is attached to it?
Both the phosphate group and nitrogenous base are attached to the central pentose sugar
Where is the nitrogenous base attached to the pentose sugar?
The nitrogenous base is attached to the 1’– carbon atom (right point)
Where is the phosphate base attached to the pentose sugar?
The phosphate base is attached to the 5’– carbon atom (left point)
What two types of nucleic acid are there?
DNA and RNA
What is DNA?
DNA (deoxyribonucleic acid) is a more stable double stranded form that stores the genetic blueprint for cells
What is RNA? (structure and role)
RNA (ribonucleic acid) is a more versatile single-stranded form that transfers the genetic information for decoding
What are both DNA and RNA polymers of?
Both DNA and RNA are polymers of nucleotides
What is the key difference in the structure of DNA and RNA?
DNA does not have a hydroxyl group on C2, just a H
What are 3 key structural differences between DNA and RNA? (categories)
Number of strands present
Composition of nitrogenous bases
Type of pentose sugar
How does DNA and RNA differ in terms of pentose sugar?
DNA - deoxyribose
RNA - ribose
How do DNA and RNA differ in terms of base composition?
DNA - AGCT
RNA - AGCU (uracil)
How do DNA and RNA differ in number of strands?
DNA - double-stranded (double helix)
RNA - single stranded
What are nucleic acids composed of? How are they linked?
Nucleic acids are composed of nucleotide monomers which are linked into a single strand via condensation reactions
What joins in a condensation reaction to from nucleic acids?
The phosphate group of one nucleotide attaches to the sugar of another nucleotide (at the 3’– hydroxyl (-OH) group)
What is the name of the bond formed between nucleotide monomers?
This results in a phosphodiester bond forming between the two nucleotides (and water is produced as a by-product)
What do the successive condensation reactions between nucleotides form?
Successive condensation reactions result in the formation of long polynucleotide strands
What are the polynucleotide chains held together by to form a double helix?
Two polynucleotide chains of DNA are held together via hydrogen bonding between complementary nitrogenous bases
How do the bases pair?
Adenine (A) pairs with Thymine (T) via two hydrogen bonds
Guanine (G) pairs with Cytosine (C) via three hydrogen bonds
In what way do the strands run and why? What is the official word?
In order for the bases to be facing each other and thus able to pair, the strands must be running in opposite directions
The two strands of DNA are described as being antiparallel
How does the atomic arrangement impact the formation of the double helix?
As the antiparallel chains lengthen, the atoms will organise themselves into the most stable energy configuration
This atomic arrangement results in the double-stranded DNA forming a double helix (~10 – 15 bases per twist)
What was Watson and Crick’s contribution to the discovery of DNA?
The structural organisation of the DNA molecule was correctly proposed in 1953 by James Watson and Francis Crick
These British scientists constructed models to quickly visualise and assess the viability of potential structures
What was Linus Pauling’s contribution to the discovery of DNA?
Their (W&C) efforts were guided by an understanding of molecular distances and bond angles developed by Linus Pauling
What was Phoebus Levene’s contribution to the discovery of DNA?
DNA is composed of nucleotides made up of a sugar, phosphate and base – Phoebus Levene, 1919
What was Erwin Chargaff’s contribution to the discovery of DNA?
DNA is composed of an equal number of purines (A + G) and pyrimidines (C + T) – Erwin Chargaff, 1950
What was Rosalind Franklin’s contribution to the discovery of DNA?
DNA is organised into a helical structure – Rosalind Franklin, 1953 (data shared without permission)
What 3 conditions did Watson and Crick’s DNA model fulfil?
DNA strands are antiparallel and form a double helix
DNA strands pair via complementary base pairing
(A = T ; C Ξ G)
Outer edges of bases remain exposed (allows access to replicative and transcriptional proteins)
What were 3 problems with the early models made by Watson and Crick?
The first model generated was a triple helix
Early models had bases on the outside and sugar-phosphate residues in the centre
Nitrogenous bases were not initially configured correctly and hence did not demonstrate complementarity
How did Franklin gather her data?
The final construction of a correct DNA molecule owed heavily to the X-ray crystallography data generated by Franklin
Why was Franklin’s data so crucial?
This data confirmed the arrangement of the DNA strands into a helical structure
