2.3 Nucleotides Flashcards
What are nucleotides?
Monomers of nucleic acids
Made of 3 subunits with one phosphate,one nitrogenous base and one sugar molecule
- Each subunit connected by a covalent group
What are the three pyramidines and what is the key feature they share?
Thymine,Uracil and Cytosine
Have 1 carbon ring
What are the two purines and what key feature do they share?
Adenine and Guanine
2 carbon based rings
How are nucleotides joined together?
- Via condensation reaction form a phosphodiester bond
What is a nucleic acid?
A chain of nucleotides
How many hydrogen bonds does each base pair in DNA form?
G-C = 3
A-T = 2
When does DNA replication occur?
- During S phase
What are the steps of DNA replication?
- Helicase causes two strands to separate by breaking h bonds between bases
- Free nucleotides pair with complimentary bases forming h bonds
- DNA polymerase joins free nucleotides
What is semi conservative replication?
Each new DNA molecule contains one original and one new strand
What is RNA?
Nucleotides whose sugars are ribose
Uracil replaces thymine
Single stranded
What is mRNA?
Complimentary DNA strand
WHat is rRNA?
RNA in ribosomes
What is tRNA?
Carries amino acids to ribosomes where polypeptides are formed
What is a gene?
Section of DNA which codes for a protein
What is a codon?
3 bases which codes for a specific amino acids
What is a start codon?
- signals the start of a sequence that codes for a protein
-AUG ( Only a start codon if at the start)
What is a stop codon?
Signals the end of a sequence of bases
What is degenerate code?
- Many amino acids can be coded for by more than one codon
What is the process of transcription?
- mRNA strand formed from free RNA nucleotides in nucleus complimentary to sense DNA strand
- mRNA strand peels away form DNA and leaves nucleus via nuclear pore
- Double helix reforms
What is the process of transcription?
- mRNA binds to ribosome at start codon
- Comlimentary tRNA molecules bind to start codon and another binds to first codon bringing amino acids with it
- Peptide bonds form between amino acids
- Ribosome continues to move along mRNA
- Repeated until stop codon is reached
