2.3 Nucleic acids Flashcards
How does RNA and DNA differ?
-In DNA the pentose sugar is deoxyribose (carbon 2 only contains a H) and RNA has the pentose sugar ribose (Carbon 2 contains OH)
-Thymine base replaced with Uracil
-RNA is small enough to leave the nucleus
-RNA nucleotides are recylced
What are the two groups for the bases and which ones belong to them and their structure?
-Pyrimidines (Thymine and Cytosine) they are smaller bases with single carbon ring structures
-Purines (Guanine and Adenine) bigger bases with double carbon ring structure
How does a Nucleotide form?
-A nucleoside and phosphoric acid join in a condensation reaction so water is released. A phosphoester bond is formed
What is the structure of a nucleotide?
Where does the phosphoester bond form between in polynucleotides?
-Carbon 3 of the sugar and phosphate group of another nucleotide
What is the structure of DNA?
-2 polynucleotide strand which run antiparallel(5’-3’ and 3’-5’) and join together forming a double helix
-Hydrogen bonds form between complementary bases (3 between C and G and 2 between A and T)
What protein allows DNA to be packed tightly?
-Histone proteins
How is ATP suited for the transfer of energy?
-Small and Soluble
-Releases energy in small quantities so energy isn’t wasted
-Unstable phosphate bond so can be easily broken down
-Easily regenerated
What is the chemical equation for the breakdown and formation of ATP?
What happens to the chromosomes just before DNA replication?
-Chromosomes become shorter, thicker and more visible
-Chromosomes duplicate into two chromatids(strands) joined at the centromere
What is the purpose of single-stranded binding proteins?
Protects the single strand from degradation during DNA replication
Where are the new nucletides that are added to the strand in DNA replication come from?
-They are free floating in the cellular fluid
What is the role of DNA polymerase in DNA replication?
-Catalases the joining of nucleotides with phosphodiester bonds
-It adds nucleotides in the 5’ to 3’ direction
What is the name of the strand that is formed continuously and discontinuously in DNA replication and what is the enzyme that fills the gap?
-Continuous=Leading strand
-Discontinuous=Lagging strand
-Ligase enzyme
How often does errors in replication occur and is this always harmful and how does the body prevent it?
-Every 10^8 base pairs
-They can lead to gene mutations but aren’t always harmful (nothing can happen or can be advantageous)
-Enzymes proofread the incorrect nucleotides and edit them out
How does DNA replication happen?
- DNA unwinds catalysed by gyrase enzyme, and hydrogen bonds between bases are brocken catalysed by DNA helicase
- The enzyme DNA polymerase catalyses the addition of new bases in the 5’ to 3’ on both strands, leading strand is done continously whereas lagging strand is discontinous
- Hydrolysis of activated nucleotides supplies energy needed and DNA replication is semi-conservative as one strand is old and one new
What does it mean when the genetic code is universal and the triplet code is degenerate?
–Universal: nearly all organisms the DNA triplet will code for the same amino acid
-Degenerate: amino acid is coded for by more than one triplet (20 amino acids and 64 possible triplets)
How does the ribosome know when to stop or start
-There are start(AUG methionine) and stop triplets( three codons) that signal to the ribosome to start or stop
What is Trna
-Involved in protein synthesis
-Made in the nucleus
-Single stranded RNA polynucleotides that fold into a three looped hairpin structure
-At the top is the amino acid site three nucleotide bases will attach to an amino acid
-At the bottom is an anticodon which is complementary to the specific codon of bases on mRNA
How does DNA transcription happen?
1.Helicase breaks down hydrogen bonds in the specific region where gene needs to be transcribed
2. RNA polymerase binds to promoter region at 5’ end and causes phosphoester bonds to form between the RNA nucleotides (free in cytoplasm) and moves in 3’ direction
3. mRNA strand seperates once formed and once RNA polymerase reaches the terminator region it detaches and mRNA leaves the nucleus
How does translation of the protein occur?
- mRNA attaches to ribosome at start codon (AUG)
2.tRNA’s anti-codon binds to complementary codon while carrying an amino acid - Ribosome moves to next codon on mRNA and a peptide bond forms between amino acids
- Another tRNA molecule enters the ribosome with an amino acid and first tRNA molecule is discharged and process repeats
- Polypeptide is released by ribosome and must undergo further processing
