1B DNA and RNA Flashcards
What do “DNA” and “RNA” stand for?
“DNA” stands for deoxyribonucleic acid and “RNA” stands for ribonucleic acid.
What are the full names of the nucleotide bases A, C, G, T and U?
The full names of the nucleotide bases (in order) are adenine, cytosine, guanine, thymine and uracil.
Why did some scientists doubt that DNA carried the genetic code when it was first discovered?
Scientists doubted that the genetic code was carried by DNA because its chemical composition is relatively simple. (Some scientists thought the genetic code must be carried by proteins instead because they are more complex.
DNA and RNA both carry information. What are their specific functions in the cell?
DNA is used to store genetic information and RNA transfers genetic information from the DNA
to the ribosomes. RNA also makes up part of the ribosomes themselves.
Describe the basic structure of a DNA nucleotide.
How does it differ from an RNA nucleotide?
A DNA nucleotide is made from a pentose sugar called deoxyribose, attached to a nitrogen-containing organic base (A, G, C or T) and a phosphate group.
An RNA nucleotide differs because contains ribose instead of deoxyribose as its pentose sugar, and uracil (U) replaces thymine (T) as a base.
Outline how nucleotides are joined together
to form a polynucleotide strand.
Nucleotides join together via condensation reactions between the phosphate group of one nucleotide and the sugar of another. This forms a polynucleotide strand, with phosphodiester bonds between the nucleotides.
Explain how DNA forms a double-helix structure.
Two DNA polynucleotide strands join together by hydrogen bonding between the bases. Each base can only join with a specific partner - this is called complementary base pairing.
In complementary base pairing, adenine always pairs with thymine (A - T) via two hydrogen bonds, and cytosine and guanine (C - G) join together via three hydrogen bonds.
The two antiparallel (running in opposite directions) polynucleotide strands then twist to form a double helix.
Draw a diagram to show how DNA forms a double helix structure.
The bar chart shows the percentage of the bases in a DNA sample that are thymine. Work out the percentages of the other DNA bases in the sample.
A = 10%, C = 40% and G = 40 %.
Due to complementary base pairing, there are equal amounts of A and T and C and G in a DNA sample.
There is the same amount of a as there is of T so percentage of A = 10%.
The percentage of G + C is therefore
(100-10-10) = 80%.
And the percentage of G or C = 80÷2=40%.
