Biological Molecules- DNA ( Year 12 content ) Flashcards
Draw the structure of a nucleotide
1) phosphate group
2) pentose sugar
3) nitrogenous base
name the pentose sugars in DNA and RNA
1) DNA: deoxyribose
2) RNA: ribose
what is the role of DNA in living cells
1)base sequence of gene codes for functional RNA and amino acid sequences of polypeptides.
2) genetic information determines inherited characteristics which influence function and structure of organisms.
State the role of RNA in living cells
mRNA: complementary sequence to 1 gene from DNA with introns( non-coding regions) spliced out
tRNA: Supplies complementary amino acids to mRNA codons during translation
How do polynucleotides form?
Condemnation reaction between nucleotides form strong phosphodiester bonds (sugar-phosphate backbone)
Describe the structure of DNA
Double helix of 2 polynucleotide strands(deoxyribose)
H-bonds between complementary purine and pyrimidine base pairs on opposite strands:
Adenine(A) + Thymine(T)
Guanine(G) + Cytosine(C)
What bases are purine and which bases are pyrimidine?
Adenine and Guanine=2-ring purine bases
Thymine, Cytosine and Uracil= 1-ring pyrimidine bases
Name the complementary base pairs in DNA
2 Hydrogen bonds between
Adenine(A) + Thymine(T)
3 Hydrogen bonds between
Guanine(G) + Cytosine(C)
Name the complementary base pairs in RNA
2 Hydrogen bonds between
Adenine(A) + Uracil(U)
3 hydrogen bonds between
Guanine(G) + Cytosine(C)
Relate the structure of DNA to its function
● sugar-phosphate backbone and many hydrogen bonds provide stability
●double-stranded for semi-conservative replication
●weak hydrogen breaks so strands seperate for replication
Describe the structure of messenger RNA(mRNA)
●long ribose polynucleotide(but shorter than DNA)
●contains the base Uracil instead of thymine
●single-stranded and linear
Relate the structure of messenger RNA(mRNA) to its functions
●breaks down quickly so no excess polypeptide forms
●Ribosome can move along the strand and tRNA can bind to exposed bases
Describe the structure of transfer RNA(tRNA)
●single strand of about 80 nucleotides
●folded into a clover shape(some paired bases)
●anticodon on one end, amino acid binding site on the other:
a) anticodon binds to complementary mRNA codon
b) amino acids correspond to anticodon
Order DNA, mRNA and tRNA according to increasing length
tRNA
mRNA
DNA
Why did scientists initially doubt that DNA carried the genetic code?
Chemically simple molecule with few components
Why is DNA replication described as ‘semi-conservative’?
●strands from original DNA molecule act as a template
●New DNA molecule contains 1 old strand and 1 new strand
Outline the process of semi-conservative DNA replication.
1) DNA helicase breaks the weak hydrogen bonds between bases which unzips the DNA forming 2 template strands
2) free nucleotides from the cytoplasm attach to exposed bases by complementary base pairing
3) DNA polymerase catalyses condensation reacts that join adjacent nucleotides on new strand
4) hydrogen bond reform
Describe the meselson-stahl experiment
1) bacteria were grown in a medium containing heavy isotope N15 for many generations
2) some bacteria were moved to a medium containing light isotope N14. Samples were extracted after 1&2 cycles of DNA replication
3)centrifugation formed a pellet. Heavier DNA( bases made from N15) settled closer to bottom of tube
4)
Explain how the meselson-stahl experiment validated semi-conservative replication
the DNA from the second round of centrifugation the band formed in the middle of the tube showing thar each DNA molecule contained a mixture of the heavier and lighter isotope of nitrogen
Describe the structure of Adenosine triphosphate(ATP)
Nucleotides derivative of adenine with 3 phosphate groups
Explain the role of of ATP in cells
ATP hydrolase catalyses ATP—> ADP+Pi
●energy released is coupled to metabolic reactions.
●phosphate group phosphorylates compounds to make them more reactive
How is ATP resynthesised in cells?
●ATP synthase catalyses condensation reaction between ADP and Pi
●during photosynthesis and respiration
Explain why ATP is suitable as the ‘energy currency’ of cells
●high energy bonds between phosphate groups
●small amounts of energy released at a time=less energy wasted as heat
●single-step hydrolysis=energy available
●readily resynthesised
