The central Dogma Review!!

What are the three components of a DNA nucleotide?

Nitrogenous base, deoxyribose sugar, and a phosphate group.

Which bases are purines and which are pyrimidines?

Purines: Adenine (A), Guanine (G). Pyrimidines: Thymine (T), Cytosine (C).

What are the base-pairing rules in DNA?

A pairs with T, C pairs with G (via hydrogen bonds).

What is the purpose of DNA replication?

To create identical copies of a DNA strand.

Which enzyme unwinds the DNA double helix?

Helicase.

What prevents DNA from re-forming a double helix during replication?

Single-stranded binding proteins.

Which enzyme prevents DNA from becoming too tightly wound?

Topoisomerase.

What does primase do?

Synthesizes an RNA primer to provide a 3’ end for DNA polymerase.

Which polymerase synthesizes new DNA?

DNA Polymerase III.

What is the difference between the leading and lagging strands?

continuous synthesis (3’ → 5’ template).
Lagging strand: discontinuous synthesis in Okazaki fragments (5’ → 3’ template).

Which enzymes are involved in finishing replication?

DNA Polymerase I (replaces primers with DNA) and DNA Ligase (joins fragments).

What is the purpose of transcription?

To create an RNA copy of a gene.

Where does RNA polymerase bind to start transcription?

The promoter region.

What strand is used as the template in transcription?

The antisense strand.

What is the purpose of translation?

To convert mRNA into a polypeptide (protein).

What is a codon?

A sequence of three nucleotides in mRNA that specifies an amino acid or stop signal.

How many codons exist, and how many code for amino acids?

64 codons total, 61 for amino acids, 3 are stop codons.

What does tRNA carry?

An anticodon (complementary to mRNA codon) and an amino acid.

What are the two subunits of a ribosome and their roles?

Small subunit (reads mRNA), large subunit (binds amino acids together).

What are the four levels of protein structure?

Primary, Secondary, Tertiary, Quaternary.

Where is DNA located in eukaryotes vs prokaryotes?

Eukaryotes: inside nucleus. Prokaryotes: in cytoplasm.

Why do eukaryotes need telomeres?

To protect chromosome ends from loss of genetic material during replication.

Which enzyme extends telomeres?

elomerase.

How do prokaryotes avoid telomere loss?

Their DNA is circular.

What classification system categorizes viruses based on mRNA production?

The Baltimore classification.

DNA replication in prokaryotes

• Origin of Replication: Single origin (OriC) on circular DNA.

• Direction: Bidirectional replication forming a replication fork.

• Key Enzymes:

  • DNA Helicase: Unwinds the DNA double helix.

  • Primase: Synthesizes RNA primers.

  • DNA Polymerase III: Main enzyme for elongation.

  • DNA Polymerase I: Removes RNA primers and fills gaps.

  • DNA Ligase: Seals nicks between Okazaki fragments.

• Leading vs Lagging Strand:

  • Leading strand: Continuous synthesis.

  • Lagging strand: Discontinuous synthesis as Okazaki fragments.

• Termination: Replication stops when forks meet at the terminus region.

• Other Notes: Circular DNA allows simultaneous replication around the loop.

What is the primary structure of a protein?

The linear sequence of amino acids in a polypeptide, held together by peptide bonds.

What is the secondary structure of a protein, and what are its main forms?

Local folding patterns stabilized by hydrogen bonds. Main forms are α-helix and β-pleated sheet.

What forces stabilize tertiary structure of a protein?

(3-D) Hydrophobic interactions, hydrogen bonds, ionic bonds, and disulfide bridges.

What is the quaternary structure of a protein?

The assembly of multiple polypeptide subunits into a functional protein, stabilized by the same forces as tertiary structure.