BM - Nucleic Acids Flashcards
What are the two types of nucleic acids?
- Deoxyribonucleic acid (DNA)
- Ribonucleic acid (RNA)
What is the monomer of nucleic acids?
A Nucleotide
What are the three components of a nucleotide?
- A pentose sugar (deoxyribose in DNA, ribose in RNA).
- A phosphate group.
- A nitrogen-containing organic base (adenine, thymine, cytosine, guanine in DNA; uracil replaces thymine in RNA).
What type of bond joins nucleotides together in a polynucleotide chain?
Phosphodiester bonds.
How is a phosphodiester bond formed?
By a condensation reaction between the phosphate group of one nucleotide and the hydroxyl group of the pentose sugar of another nucleotide.
What is the structure of DNA?
DNA is a double-stranded helix where two polynucleotide chains are held together by hydrogen bonds between complementary base pairs.
What are the complementary base pairs in DNA?
Adenine (A) pairs with Thymine (T) via two hydrogen bonds.
Cytosine (C) pairs with Guanine (G) via three hydrogen bonds.
How does the structure of RNA differ from DNA?
RNA is single-stranded, while DNA is double-stranded.
The sugar in RNA is ribose, whereas in DNA it is deoxyribose.
RNA contains uracil (U) instead of thymine (T).
What are the three types of RNA and their roles?
- mRNA (messenger RNA): Carries the genetic code from DNA to the ribosome for protein synthesis.
- tRNA (transfer RNA): Brings specific amino acids to the ribosome during translation.
- rRNA (ribosomal RNA): Combines with proteins to form ribosomes.
What is the process of DNA replication called?
Semi-conservative replication
Describe the process of semi-conservative DNA replication.
- DNA helicase unwinds the DNA double helix by breaking hydrogen bonds between complementary bases.
- Each strand acts as a template.
- Free DNA nucleotides pair with complementary bases on the template strands.
- DNA polymerase catalyzes the formation of phosphodiester bonds between adjacent nucleotides.
- Two identical DNA molecules are formed, each containing one original strand and one new strand.
What is the role of DNA helicase in DNA replication?
DNA helicase unwinds the DNA double helix and breaks the hydrogen bonds between complementary bases, separating the two strands.
What is the role of DNA polymerase in DNA replication?
DNA polymerase catalyzes the formation of phosphodiester bonds between adjacent nucleotides, synthesizing the new DNA strand in the 5’ to 3’ direction.
What evidence supports the semi-conservative model of DNA replication?
The Meselson and Stahl experiment using isotopes of nitrogen (N-15 and N-14) demonstrated that each new DNA molecule contains one original and one newly synthesized strand.
What is the role of ATP in nucleic acid synthesis?
ATP provides the energy needed for the formation of phosphodiester bonds during nucleic acid synthesis.
Name the type of bond between:
1. complementary base pairs
1. adjacent nucleotides in a DNA strand
- Hydrogen (bonds);
- Phosphodiester (bonds);
Describe the structure of DNA
5 marks
- Polymer of nucleotides;
- Each nucleotide formed from deoxyribose, a phosphate (group) and an organic/nitrogenous base;
- Phosphodiester bonds (between nucleotides);
- Double helix/2 strands held by hydrogen bonds;
- (Hydrogen bonds/pairing) between adenine, thymine and
cytosine, guanine;
Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule.
2 marks
) 1. Condensation (reaction)/loss of water;
2. (Between) phosphate and deoxyribose;
3. (Catalysed by) DNA polymerase;
Name the protein associated with DNA in a chromosome.
Histone;
In the process of semi-conservative DNA replication, the two strands within a DNA molecule are separated. Each then acts as a template for the formation of a new complementary strand.
Describe how the separation of strands occurs.
2 marks
- DNA helicase;
- Breaks hydrogen bonds between base pairs/ AT and GC
Describe the role of DNA polymerase in the semi-conservative replication of DNA
3 marks
- Joins (adjacent DNA) nucleotides;
- (Catalyses) condensation (reactions);
- (Catalyses formation of) phosphodiester bonds (between adjacent nucleotides);
Name the two scientists who proposed models of the chemical structure of
DNA and of DNA replication.
Watson and Crick
A scientist replicated DNA in a test tube. To do this, he mixed an enzyme with
identical single-stranded DNA fragments and a solution containing DNA nucleotides.
(b) Name the enzyme used in this DNA replication.
DNA polymerase;
Use your knowledge of semi-conservative replication of DNA to suggest:
1. the role of the single-stranded DNA fragments
2. the role of the DNA nucleotides.
Role of single-stranded DNA fragments
1. Template;
2. Determines order of nucleotides/bases;
Role of DNA Structure
3. Forms complementary pairs / A – T, G - C
OR
Forms complementary (DNA) strand;
Give features of DNA and explain how each one is important in the
semi-conservative replication of DNA.
- Weak / easily broken hydrogen bonds between bases allow two
strands to separate / unzip; - Two strands, so both can act as templates
- Complementary base pairing allows accurate replication;
Describe the role of two named enzymes in the process of semiconservative replication of DNA.
3 marks
- (DNA) helicase causes breaking of hydrogen between DNA
strands - DNA polymerase joins the (DNA) nucleotides;
- Forming phosphodiester bonds;
Adenosine triphosphate (ATP) is a nucleotide derivative.
Contrast the structures of ATP and a nucleotide found in DNA to give two
differences.
3 marks
- ATP has ribose and DNA nucleotide has deoxyribose;
- ATP has 3 phosphate (groups) and DNA nucleotide has 1 phosphate
- ATP – base always adenine and in DNA nucleotide base can be C, T or G
Other than being smaller, give two ways in which prokaryotic DNA is different
from eukaryotic DNA.
- Prokaryotic DNA is Circular / non-linear (DNA);
- Not (associated) with proteins / histones;
- No introns in prokaryotic cells
DNA is a polymer. What is the evidence is there that DNA is a polymer?
- repeating units
