1.5 Nucleic Acids + 1.6 ATP Flashcards
What makes up a nucleotide
Phosphate group
Organic base
Pentose sugar
Name Pentose sugars in DNA and RNA
Deoxyribose (DNA) and Ribose (RNA)
State role of DNA in living cells
Base sequence of genes that code for functional RNA and amino acid sequence of polypeptides
Genetic info determines inherited characteristics= influences structure and function of organisms
State role of RNA in living cells
mRNA: complementary sequence to 1 gene from DNA with introns spliced out. Codons can be translated into a polypeptide by ribosomes
rRNA: component of ribosomes, along with proteins
tRNA: supplies complementary amino acids to mRNA codons during translation
How do polynucleotides form
Condensation reaction between nucleotides form strong phosphodiester bonds, sugar phosphate backbone
Describe structure of DNA
Double helix of 2 polynucleotide strands (deoxyribose)
H-bonds between complementary purine and pyrimidine base pairs on opposite strands:
A+T, G+C
Which bases are purine and/ or pyrimidine
A&G = 2 ring purine base
T&C&U = 1 ring pyrimidine base
Name complementary base pairs in DNA
2 H-bonds between adenine and thymine
3 H-bonds between guanine and cytosine
Name complementary base pairs in RNA
Same as DNA except instead of thymine it’s 2 H-bonds between adenine and uracil
Relate structure of DNA to its functions
• sugar phosphate backbone and many H-bonds provide stability
• long molecule stores lots of info
• helix is compact for storage and functions
• base sequence of triplets codes for amino acids
• double stranded for semi conservative replication
•complementary base pairing for accurate replication
• weak H-bonds break so strands separate for replication
Describe structure of messenger RNA (mRNA)
•long Ribose polynucleotide (but shorter than DNA)
•contains uracil instead of thymine
•single stranded and linear (no complementary base pairing)
•codon sequence is complementary to exons of 1 gene from 1 DNA strand
Relate structure of mRNA to its functions
• breaks down quickly so no excess polypeptide forms
• ribosome can move along strand and tRNA can bind to exposed bases
• can be translated into a specific polypeptide by ribosomes
Describe structure of transfer RNA (tRNA)
•single strand of about 80 nucleotides
•folded into clover shape (some paired bases)
• anticodon on one end, amino acid binding site on other:
a) anticodon bonds to complementary mRNA codons
b) amino acids corresponds to anticodon
Order DNA, mRNA, and tRNA according to increasing length
tRNA, mRNA, DNA
Why did scientists initially doubt that DNA carried genetic code
chemically simple molecule with few compliments
Why’s DNA replication described as semiconservative
• strands from original DNA molecule act as a template
• new DNA molecule contains 1 old strand and 1 new strand
Outline process of semiconservative DNA replication
- DNA helicase breaks H-bonds between base pairs
- Each strand acts as a template
- Free nucleotides from nuclear sap attach to exposed bases by complementary base pairing
- DNA polymerase catalyses condensation reactions that join adjacent nucleotides on new strand
- H- bonds reform
describe Meselson and Stahl experiment
- Bacteria were grown in medium containing heavy isotope N¹⁵ for many generations
- Some bacteria were moved to a medium containing light isotope N¹⁴. Samples were extracted after 1 and 2 cycles of DNA replication
- Centrifugation formed a pellet. Heavier DNA (bases made from N¹⁵) settled closer to bottom of tube
Explain how Meselson and Stahl experiment validated semiconservative replication
Grown in N¹⁵
1 division: all molecules have 1 strand of N¹⁵ and 1 strand of N¹⁴
2 division 50% has 2 strands N¹⁴, 50% has 1 strand N¹⁵ and 1 strand N¹⁴
Describe structure of Adenosine Triphosphate (ATP)
Nucleotide derivative of adenine and 3 phosphate
Explain role of ATP in cells
ATP hydrolyse catalyses into ADP and Pi
•energy released is coupled to metabolic reactions
•phosphate group phosphorylates compounds to make them more reactive
How’s ATP resynthesised in cells
ATP synthase catalyses condensation reactions between ADP and Pi
During photosynthesis and respiration
Explain why ATP is suitable as energy currency in cells
High energy bonds between phosphate groups
Small bursts of energy released at a time= less energy wasted as heat
Single step hydrolysis = energy available quickly
Readily resynthesised
