3.8 Nucleic Acids Flashcards
Where were nucleic acids discovered?
Cell nuclei
What are the 2 types of nucleic acids?
DNA and RNA
What is the function of nucleic acids?
Storage and transfer of genetic material.
Synthesis of polypeptides (proteins).
What elements do nucleic acids contain?
C, H, O2, N, P
What are nucleic acids? How are they formed?
Large polymers formed from many nucleotides (monomers) linked in a chain
A nucleotide is made up of three components. Name them.
- A pentose monosaccharide, containing 5 carbon atoms
- A phosphate group, (-PO4)2-, an inorganic molecule that’s acidic and negatively charged
- A nitrogenous base - complex organic molecule containing 1 or 2 carbon rings and a nitrogen in its structure
How are nucleotides linked together?
By condensation reactions to form a polymer called a polynucleotide
Describe the structure of polynucleotides.
Phosphate group @ 5th carbon of pentose sugar of one nucleotide forms a covalent bond with hydroxyl group at 3rd carbon of the pentose sugar.
Describe the structure of what’s formed after 2 nucleotides are linked by condensation reactions?
Long, strong sugar-phosophate backbone, with a base attached to each sugar
What are phosphodiester bonds broken by?
Hydrolysis - reverse of condensation reaction, releasing the nucleotides
What does DNA stand for?
Deoxyribonucleic acid
What type of sugar is DNA?
Deoxyribose - sugar w/ one less O atoms than ribose
DNA is composed of 4 bases. What 2 groups are these bases broken into?
Pyrimadines
Purines
What are pyrimadines?
Smaller bases, containing single carbon ring structures.
T and C
What are purines?
Larger bases, containing double carbon ring structures.
A and G
What are the 2 strands of a DNA double helix held by?
H bonds
Describe specifically how 2 strands of DNA double helix are held together.
Each strand has a phosphate group, C5, at one end and a hydroxyl group, C3, at the other
Why are the 2 strands of a DNA helix said to be antiparallel?
The strands are arranged so that they run in opposite directions
How many H bonds hold C and G together?
3
How many H bonds hold A and T together?
2
Define complementary base pairing.
Specific H bonding between nucleic acid bases.
A/U binds to T, C binds to G
What do the complementary base pairing rules mean in terms of how DNA bases bond?
Small pyrimidine bases always binds to larger purine base.
This arrangement maintains a constant distance between DNA backbones, resulting in parallel polynucleotide chains
What else does complementary base pairing ensure?
DNA always has equal amounts of A and T, and C and G
What carries an organism’s genetic code?
Order of sequence of bases along a DNA strand
What does RNA play a role in?
Transfer of genetic information from DNA -> proteins that make up enzymes and tissues
What does DNA store?
All the genetic info needed by an organism
DNA of eukaryotes is long, compromising hundreds of genes. What is the problem with this?
DNA is too big to leave the nucleus to supply info directly to sites of protein synthesis
How do eukaryotes get over the problem of DNA being too large to leave the nucleus?
A short section of DNA containing 1 gene is transcribed into a short mRNA molecule.
Each mRNA is shorter than the chromosome of DNA.
Describe the structure of mRNA
Polymer composed of many nucleotide monomers
What’s the difference between DNA and mRNA?
DNA sugar = deoxyribose
mRNA sugar = ribose
DNA = T + A mRNA = U + A (Uracil replaces thymine)
Is there a difference between Uracil (U) and Adenine (A)?
No - U still forms 2 H bonds with A
Do nucleotides with U instead of T form in the same way?
Yes - by forming phosphodiester bonds through condensation reactions
If the problem is that DNA itself is too big to leave the nucleus, how does turning it into RNA polymers help?
The RNA polymers are small enough to leave the nucleus - they can travel to ribosomes and trigger protein synthesis
What happens to RNA molecules after protein synthesis?
RNA is degraded in the cytoplasm - phosphodiester bonds are hydrolysed and RNA nucleotides are released + reused
