Nucleic Acids & DNA replication🧬 Flashcards
What is the structure of a nucleotide?
- Pentose sugar
- Nitrogenous base
- Phosphate group
Structure of DNA
•Deoxyribose sugar •Phosphates bonded to pentoses by covalent bonds (condensation) •Nitrogenous base •Double stranded •Sugar phosphate backbones are anti-parallel -form a double helix •Contains pyrimidines: C and T •Contains purines: A and G
Structure of RNA
- Ribose sugar
- Phosphates groups
- Single stranded
- Contains pyrimidines: C and U
- Contains purines: A and G
- Tend to be short lived
What is a pyrimidine?
- A base with a single ring structure
- Cytosine
- Thymine
- Uracil
What is a purine?
- A base with a double ring structure
- Adenine
- Guanine
How are polynucleotides formed?
- One nucleotide can join to another by a condensation reaction
- Takes place between the sugar and phosphate groups
- Many nucleotides joining up this way form a polynucleotide chain
What is a nucleoside?
- Organic base + pentose sugar but no phosphate
- Nucleoside monophosphate (1p)
- Nucleoside diphosphate (2p)
- Nucleoside triphosphate (3p)
- Phosphorylated nucleoside (2/3p)
What is the structure of ATP?
- Adenine nitrogenous base
- Ribose
- 3 phosphate groups
- Forms a phosphorylated nucleotide
What are the similarities and differences between ATP, RNA & DNA?
•All made of a pentose sugar
-containing a phosphate group
•Made of different pentose sugars
•Contain different number of phosphate groups
Hydrolysis of ATP
ATP + water
(Hydrolysis)—>
(Condensation)
What is an exergonic reaction?
A reaction that releases energy
E.g. ATP hydrolysis
What are the advantages of ATP as a supplier of energy?
•Hydrolysis involves a single reaction that releases energy immediately - glucose takes longer
•Only one enzyme is needed to release energy from ATP compared to many in glucose
•ATP releases energy in small amounts, when & where it is needed, so no energy is wasted
-glucose releases large amounts of energy all at once
•ATP is a universal source of energy
•Readily available as the phosphate group is transferred on demand
What is ATP synthase?
- Catalyses condensation reaction to produce ATP
* During respiration or photosynthesis
What are the roles of ATP?
•Metabolic processes -building large, complex molecules •Active transport -change shape of carrier proteins and allow molecules/ions to move against a conc gradient •Movement -for muscle contraction •Nerve transmissions -sodium-potassium pumps •Secretions -packaging into vesicles •Homeostasis -energy lost as heat from ATP hydrolysis •Adding phosphate groups to proteins
What is the complimentary base pairing rule?
- Adenine must always pair with Thymine (or Uracil in RNA)
* Cytosine must always pair with Guanine
What are the two main functions of DNA?
- DNA replication
* Protein synthesis
What is the process of DNA replication?
- Helicase enzyme breaks hydrogen bonds between complementary strands
- Both strands are used as templates
- Free nucleotides pair with complementary bases now exposed
- Hydrogen bonds form between the bases
- DNA polymerase joins adjacent nucleotides by condensation reactions, forming phosphodiester bonds
- 2 identical DNA molecules are produced
What is the semi-conservative idea?
Each new DNA molecule contains one original strand and one newly formed strand
Describe Meselson and Stahl’s experiment
- Grew E.coli in a medium containing amino acids with the isotope 15N (heavy nitrogen)
- Bacterium’s DNA contains 15N
- Centrifuged DNA in caesium chloride solution
- DNA settles depending on mass
- 15N bacteria transferred to a growth medium containing 14N (light)
- Bactria divided
- 1st gen 50% 15N (og), 50% 14N (new)
- 2nd gen 25% 15N, 75% 14N
Explain Meselson and Stahl’s experiment
- At succeeding generation times, the DNA extracts were found to have a lower proportion of 15N
- More 14N was incorporated into the bacterial DNA
- Due to semi-conservative theory
What is a nucleic acid?
A polymer of nucleotides
What is a sugar-phosphate backbone?
The deoxyribose of one nucleotide forms a bond with the phosphate of another nucleotide to form a sugar-phosphate backbone
What bonds hold the two strands of double helix together?
Hydrogen bonds between a pair of nitrogenous bases
What does the complementary base pairing rule ensure?
- DNA replicates correctly
* Same proportion of A/T and C/G
