DNA and RNA Structure Quiz

DNA Structure and Replication

• DNA is a double helix, 3.4 nm per full turn, 10 base pairs per turn, base pair ~0.34 nm
• Two strands are anti-parallel
• A=T; G=C, hydrogen bonds, complementary base pairing
• Radius = 1 nm
• Sugar-phosphate backbone linked by phosphodiester bonds
• Nucleotides consist of a pentose sugar (ribose/deoxyribose), a nitrogenous base, and a phosphate group
• DNA molecule binds with histones, forming nucleosomes, which condense further into chromatin fibers, ultimately forming chromosomes
• DNA replication is semi-conservative, resulting in two new DNA strands that are exact replicas of the parent strand

Nucleic Acids

• Monomers are nucleotides
• Functions include storage and transmission of genetic information, structural or catalytic roles
• Two types found in living organisms: Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA)

Structure of RNA

• Similar to DNA, but uracil replaces thymine and ribose replaces deoxyribose
• Single polynucleotide chain
• Three types of RNA:
  • Messenger RNA (mRNA)
  • Transfer RNA (tRNA)
  • Ribosomal RNA (rRNA)

DNA Replication

• Base pairing allows existing DNA strands to serve as templates for new complementary strands.
• When a cell copies DNA, the two strands unwind/untwist, each serving as a template
• Enzymes link nucleotides to form a new strand.
• Creates two DNA strands (exact copies of parent), following the semi-conservative model

Protein Synthesis

• A polypeptide is coded for by a gene, which is a sequence of nucleotides in a DNA molecule.
• DNA's information is used during transcription and translation
• mRNA, tRNA, and ribosomes play crucial roles
• Transcription: synthesis of mRNA under DNA's direction. Non-coding strand of DNA serves as a template for mRNA. Free RNA nucleotides attach to the template (catalyzed by RNA polymerase).
• Translation: actual synthesis of a polypeptide. Occurs under the direction of mRNA. mRNA base sequence is translated into amino acid sequence of a polypeptide. Stages include: mRNA carrying information to ribosomes, amino acid activation, translation, and functional protein production.

The Central Dogma of Molecular Biology

• First expressed by Francis Crick
• Detailed transfer of sequential information
• Genetic information flows from DNA into protein, but not back

Genetic Code

• Triplet code: genetic instructions for a polypeptide chain are written in DNA as 3-nucleotide words
• DNA stores information as sequences of bases
• The genetic code is degenerate (more than one codon can code for the same amino acid)
• Non-overlapping code: each DNA base only contributes to coding for one amino acid
• Universal code: the DNA base triplets code for the same amino acids in all organisms.

Transcription and Translation

• Transcription produces mRNA (RNA synthesis under DNA's direction), unique sequence of RNA nucleotide. mRNA serves as genetic message.
• Translation is the actual synthesis of a polypeptide. Changes language(nucleotide → amino acid). Translation occurs under the direction of mRNA
• Both nucleic acids have the same language.

Stages of Protein Synthesis

• Stage 1: Transcription DNA unwinds, hydrogen bonds break, forming mRNA using DNA's non-coding strand. Free RNA nucleotides attach to the template DNA
• Stage 2: mRNA carries information to ribosomes mRNA exits nucleus and enters cytoplasm
• Stage 3: Amino Acid Activation tRNA molecules carry specific amino acids
• Stage 4: Translation Each mRNA codon attracts a tRNA with the complementary anticodon. Peptide bonds form between amino acids. tRNA detaches and leaves ribosome, mRNA eventually degrades.
• Stage 5: Functional Protein Produced Completed polypeptide processed by cellular machinery to create final functional protein (e.g., enzyme).

Test your knowledge on the structure and replication of DNA and the characteristics of RNA. This quiz covers key concepts such as base pairing, nucleotides, and the roles of nucleic acids in genetic information storage and transmission. Perfect for students studying molecular biology.