Nucleic acids (2) Flashcards
Draw the structure of a nucleotide.
look at diagram in notes
What is the role of DNA in living cells?
- base sequence of gene codes for functional RNA + amino acid sequence of polypeptides
- genetic information determines inherited characteristics which influences structure + function of organisms
What are the 3 types of RNA?
mRNA
rRNA
tRNA
What is the role of mRNA in living cells?
complementary sequence to 1 gene from DNA with introns spliced out so codons can be translated into a polypeptide by ribosomes
What is meant by an intron?
non-coding region
What is the role of rRNA in living cells?
component of ribosomes
What is the role of tRNA in living cells?
supplies complementary amino acids to mRNA codons during translation
How do polynucleotides form?
condensation reactions between nucleotides form strong phosphodiester bonds
What is the structure of DNA?
- double helix of 2 polynucleotide strands (deoxyribose)
- H-bonds between complementary purine and pyrimidine base pairs on opposite strands
What are the 4 bases in DNA?
adenine + thymine
guanine + cytosine
How many bonds are between each of the base pairs in DNA?
A + T have 2 H-bonds between
G + C have 3 H-bonds between
What type of base are A and G?
2-ring purine bases
What type of base are T, C and U?
1-ring pyrimidine bases
Which bases are 2-ring purine?
A and G
Which bases are 1-ring pyrimidine?
T, C and U
What are the 4 bases in RNA?
adenine + uracil
guanine + cytosine
Rank DNA, mRNA and tRNA from shortest to longest.
tRNA - mRNA - DNA
What are 5 structures of DNA?
- sugar-phosphate backbone
- base sequence of triplets
- double-stranded
- complementary base pairing
- many H-bonds
What are 3 structures of mRNA?
3
- contains uracil not thymine
- single-stranded and linear
- codon sequence is complementary to exons of 1 gene from 1 DNA strand
What is the structure of tRNA?
- single strand of about 80 nucleotides
- folded into clover shape
- anticodon on 1 end and amino acid binding site on the other
What does the anticodon on tRNA do?
binds to complementary mRNA codon
What did some scientists initially doubt and why?
Initially doubted DNA carried the genetic code as it’s a chemically simple molecule with few components
What are 2 reasons why DNA replication is called semi-conservative?
- strands from original DNA molecule act as a template
- new DNA molecule contains 1 old strand and 1 new strand
What are the 5 steps of semi-conservative DNA replication?
1) DNA helicase breaks H-bonds between base pairs
2) each strands acts as a template
3) free nucleotides from nuclear sap attach to exposed bases by complementary base pairing
4) DNA polymerase catalyses condensation reactions that join adjacent nucleotides on new strand
5) H-bonds reform
What were the 4 steps of the Meselson-Stahl experiment?
1) bacteria were grown in a medium containing heavy isotope 15N for many generations
2) some bacteria were moved to a medium containing light isotope 14N
3) samples were extracted after 1 and 2 cycles of DNA replication
4) centrifugation formed a pellet - heavier DNA (bases made from 15N) settled closer to bottom of tube
What was the name of the experiment using 14N and 15N?
Meselson-Stahl experiment
How does having a sugar-phosphate backbone and many H-bonds relate to DNA’s function?
provides stability
How does having a base sequence of triplets relate to DNA’s function?
code for amino acids
How does being double-stranded relate to DNA’s function?
for semi-conservative replication
How does having complementary base pairing relate to DNA’s function?
for accurate replication
How does having H-bonds relate to DNA’s function?
they are weak so break so strands separate for replication
How does containing uracil not thymine relate to mRNA’s function?
breaks down quickly so no excess polypeptide forms
How does being single-stranded and linear relate to mRNA’s function?
so ribosome can move along strand and tRNA can bind to exposed bases
How does having a codon sequence complementary to exons of 1 gene from 1 DNA strand relate to mRNA’s function?
so can be translated into specific polypeptide by ribosomes
