Flashcards in Nucleic Acids + Protein Synthesis (Chapter 6) Deck (55)
What are the two types of nucleic acid?
DNA and RNA
What does DNA stand for?
What does RNA stand for?
What are nucleic acids?
Polymers - made up of many nucleotides
What is a polymer?
A molecule made of many similar, smaller molecules joined in a long chain
What are nucleotides?
The smaller molecules from which DNA and RNA are made
Describe the structure of a nucleotide
Made up of 3 smaller components:
1) A nitrogen containing (nitrogenous) base
2) A pentose sugar
3) A phosphate group
What are the 5 different types of bases?
Both: Adenine, Cytosine, Guanine
What is the structure of a purine base?
A double ring structure
What is the structure of a pyrimidine base?
A single ring structure
Which ones are the purine bases?
Adenine and Guanine
Which ones are the pyrimidine bases?
Cytosine, Thymine and Uracil
Which base does Uracil replace in RNA?
What is the pentose sugar in DNA?
What is the pentose sugar in RNA?
What is adenosine?
Adenine with a sugar joined to it
What is ATP?
Adenosine triphosphate - adenosine combined with three phosphate groups (v. similar to adenine nucleotide just with two extra phosphate groups and sugar has an extra OH group)
How are the polynucleotides (DNA and RNA) formed?
Many nucleotides are linked together into a long chain
- they are formed of alternating sugars and phosphates linked together, with the bonds projecting sideways
- the covalent sugar-phosphate bonds (phosphodiester bonds) link the 5-carbon of one sugar molecule and the 3-carbon of the next
- the polynucleotide is said to have 3' and 5' ends
Where and when does the formation of polynucleotides take place?
Inside the nucleus, during interphase
Describe the structure of DNA molecules
- They are made of two polynucleotide strands lying side by side, running in opposite directions (antiparallel)
- The two strands are held together by H-bonds between the bases
Which bases out of purine or pyrimidine are bigger and what does this mean for the DNA molecule?
Purine bases are bigger
- therefore, in a DNA molecule, there is just enough room between the two sugar-phosphate backbones for one purine and one pyrimidine molecule
- therefore, a purine in one strand must always be opposite a pyrimidine in the other
What is complementary base pairing?
Adenine always pairs with thymine, while cytosine always pairs with guanine
What is the 3D shape of the DNA molecule?
A double helix
How can DNA replication and protein synthesis occur?
- The H-bonds linking the bases (and holding the strands together) can be broken relatively easily
- This happens during both of these processes
- The breaking of the H-bonds is a very important feature of the DNA molecule that enables it to perform its role in the cell
Describe the structure of RNA molecules?
They remain as single strand polynucleotides and can form very different 3D structures
Describe semi-conservative replication
Watson and Crick suggested that the two strands of the DNA molecule could split apart
- new nucleotides line up along each strand, opposite their appropriate partners, and join up to from complementary strands along each half of the original molecule
- the new DNA molecules are just like the old ones, because each base only pairs with its complementary one
- each pair of strands then winds up again into a double helix
Why is it called semi-conservative replication?
Because half of the original molecule is kept in each of the new molecules
Explain what happens during semi-conservative replication
1) The DNA double helix unwinds as the H-bonds between the bases break - both strands of DNA act as templates
2) Each of the bases of free activated (phosphorylated) nucleotides in the nucleus pairs up with its complementary base of each of the parent DNA strands - the process continues along the whole of the DNA molecule
3) DNA polymerase catalyses the reaction by linking the sugar and innermost phosphate group of next door nucleotides, forming the sugar-phosphate backbone
How is the DNA molecule copied perfectly many times over?
DNA polymerase will only link an incoming nucleotide to the growing new chain if it is complementary to the base on the old strand (mistake only 1 in every 10^8 base pairs)