Overview
This lecture covers the similarities and differences between DNA and RNA, their structures, and their key roles in protein synthesis.
DNA vs. RNA: Structure and Location
- DNA and RNA are nucleic acids found in all living organisms.
- In eukaryotes, DNA is mainly in the nucleus; RNA is found both in and out of the nucleus.
- Prokaryotes lack a nucleus but have both DNA and RNA.
- DNA is generally double-stranded and forms a double helix; RNA is usually single-stranded.
Nucleotides and Components
- Both DNA and RNA are made of nucleotides, the building blocks of nucleic acids.
- Each nucleotide has three parts: phosphate, sugar, and base.
- DNA’s sugar is deoxyribose; RNA’s sugar is ribose.
- DNA stands for deoxyribonucleic acid; RNA stands for ribonucleic acid.
Nitrogenous Bases and Pairing Rules
- DNA bases: adenine (A), thymine (T), guanine (G), cytosine (C); A pairs with T, C pairs with G.
- RNA bases: adenine (A), uracil (U), guanine (G), cytosine (C); A pairs with U, C pairs with G.
Roles in Protein Synthesis
- DNA stores genetic information and codes for traits but requires RNA to express these genes.
- mRNA (messenger RNA) carries the code from DNA to ribosomes.
- rRNA (ribosomal RNA) is a key component of ribosomes, where proteins are made.
- tRNA (transfer RNA) brings amino acids to ribosomes, matching them to mRNA codons to build polypeptides.
Example Questions and Solutions
- 8 DNA nucleotides have 8 bases; in double-stranded DNA, that's 4 base pairs.
- If DNA strand has A, T, T, G, A, C, its complementary strand is T, A, A, C, T, G.
- For the same DNA sequence, complementary RNA (mRNA) is U, A, A, C, U, G (uracil replaces thymine).
Key Terms & Definitions
- Nucleic Acid — biomolecule that stores genetic information (DNA and RNA).
- Nucleotide — monomer of nucleic acids; consists of phosphate, sugar, base.
- Antiparallel — describes the opposite orientation of DNA strands.
- Codon — three-base sequence on mRNA coding for an amino acid.
- Polypeptide — chain of amino acids; forms proteins.
Action Items / Next Steps
- Watch the protein synthesis video for more detail on mRNA, rRNA, and tRNA.
- Refer to linked readings for further exploration of nucleic acid structures.