Central Dogma of Molecular Biology Quiz

Central Dogma: Chromosome Organization, DNA Replication, and mRNA Processing

• Bacterial chromosomal DNA is circular and compacted about 10,000-fold through loop domains and DNA supercoiling.

• Eukaryotic chromosomes are linear and compacted through interactions between DNA and histone proteins, forming nucleosomes.

• Nucleosomes consist of double-stranded DNA wrapped around an octamer of histone proteins, shortening DNA length about seven-fold.

• Histone proteins are basic and contain many positively-charged amino acids that bind with the phosphates along the DNA backbone.

• Euchromatin is less condensed and transcriptionally active, while heterochromatin is tightly compacted and transcriptionally inactive.

• DNA replication involves three modes: semiconservative, conservative, and dispersive, and enzymes including DNA polymerase, DNA gyrase/topoisomerase, DNA ligase, helicase, and primase.

• DNA polymerase catalyzes the synthesis of DNA from 5' to 3' direction and has 5'→3' polymerase activity, 5'→3' exonuclease activity, and 3'→5' exonuclease activity.

• DNA gyrase/topoisomerase opens coiled turns in DNA to allow unwinding, while DNA ligase joins two pieces of DNA by forming a phosphodiester bond.

• Helicase unwinds DNA and forms single-stranded DNA at the replication fork, while primase synthesizes a sequence-specific RNA molecule to serve as the primer for DNA synthesis.

• DNA replication in the lagging strand occurs in pieces called Okazaki fragments and requires multiple primosome formations.

• During transcription, RNA polymerase binds to the gene's promoter, moves along the gene encoding sequence, and adds new RNA nucleotides in the 5'→3' direction.

• Processing of pre-mRNA includes adding a 5' cap and poly-A tail, and splicing out introns to form mature mRNA.The Central Dogma of Molecular Biology and Protein Synthesis

• Transcriptional modifications remove introns from pre-mRNA molecules before leaving only exons for translation.

• Splicing of pre-mRNA molecules occurs in spliceosomes, which contain ribozymes and small nuclear RNAs (snRNA).

• mRNA carries a series of codons, which are blocks of three consecutive nucleotide bases that specify a particular amino acid.

• Start codons specify the start of RNA translation, while stop codons specify the end of RNA translation.

• Transfer RNA (tRNA) binds to an anticodon on one side and an amino acid on the other, with each anticodon complementary to an mRNA codon.

• Ribosomes facilitate the specific coupling of tRNA anticodons with mRNA codons and have a large and a small subunit composed of proteins and ribosomal RNA (rRNA).

• The genetic code is encoded as a sequence of base triplets (codons) that are read in the 5’->3’ direction along the mRNA during translation.

• Different arrangements of DNA triplets encode each of the 20 amino acids that make proteins.

• Translation can be divided into three stages: initiation, elongation, and termination.

• Initiation involves a start codon (AUG) complementing with the Methionine (Met) tRNA in the P site of the ribosome, while the A site is open and ready to receive new tRNAs.

• Elongation consists of a series of three-step cycles as each amino acid is added to the preceding one.

• Termination occurs when one of the three stop codons reaches the A site, and all parts are released.