DNA Structure and Replication Quiz

DNA Structure and Replication

• Deoxyribonucleic acid (DNA) is a large complex molecule that carries genetic information, determining human traits.
• DNA is a polymer made of nucleotides (sugar, phosphate, and nitrogenous base).
• DNA bases: adenine (A), thymine (T), cytosine (C), and guanine (G).
• Chargaff's rule: A pairs with T, and C pairs with G.
• DNA is antiparallel, meaning the two strands run in opposite directions (5' to 3' and 3' to 5').
• DNA replication ensures that each new cell receives a complete copy of the genetic information.
• DNA replication is semiconservative; each new DNA molecule is composed of one original strand and one newly synthesized strand.
• Leading strand: synthesized continuously in the 5' to 3' direction.
• Lagging strand: synthesized discontinuously in short fragments (Okazaki fragments) and then joined by DNA ligase.
• Enzymes involved in replication include helicase, single-strand binding proteins, topoisomerases, DNA polymerase, and primase.
• Okazaki fragments are short segments of DNA synthesized discontinuously during replication of the lagging strand.

DNA Replication - More Detail

• Helicase unwinds the DNA double helix at replication origins.
• Single-strand binding proteins stabilize the separated strands.
• Topoisomerases relieve the strain created by unwinding.
• DNA polymerase adds new nucleotides complementary to the template strand.
• DNA polymerase works in one direction 5' to 3'
• RNA primase creates RNA primers to initiate DNA synthesis (leading and lagging strands).
• RNA primers are removed and replaced with DNA nucleotides.
• DNA ligase joins the Okazaki fragments.
• Mismatch repair corrects errors during replication.

RNA and Protein Synthesis

• Ribonucleic acid (RNA) carries genetic information from DNA to the ribosomes, where proteins are constructed
• Types of RNA: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).
• Transcription: synthesis of mRNA from a DNA template.
• Stages of transcription: initiation, elongation, and termination.
• RNA processing involves adding a 5' cap and a 3' poly-A tail to mRNA molecules and splicing out introns, leaving only exons.
• Translation: conversion of mRNA to a polypeptide (protein).
• Initiation: mRNA binds to ribosome; tRNA brings the first amino acid.
• Elongation: codons on mRNA are read, tRNA brings amino acids, peptide chain grows.
• Termination: stop codon signals the end of translation.

Genetic Variation

• Mutations are changes in DNA sequences.
• Mutations can be silent, missense, or nonsense.
• Mutations can be caused by various factors including errors in replication or exposure to mutagens.
• Somatic mutations affect the cells of an organism, while germline mutations affect the sex cells and can be passed to future generations.
• Frameshift mutations alter the reading frame of the genetic code.
• Other mutations mentioned include insertion, deletion, and base substitutions.

Genes and Viruses

• Genes are segments of DNA that contain the code for proteins/traits.
• A retrovirus contains RNA that is reversed transcribed to DNA
• Viruses replicate using the host's cellular machinery and may lead to diseases.
• Viruses can undergo two lifecycles: lytic (destructive) and lysogenic (dormant).
• Bacteriophages are viruses that infect bacteria.
• Transduction is when viruses acquire bits of bacterial DNA resulting in recombination.
• Genetic recombination can occur during the process of sexual reproduction in eukaryotes.

Bacterial Genetics

• Bacteria have circular DNA in the nucleoid region.
• Bacteria replicate DNA in both directions, mostly by binary fission.
• Bacterial transformation: take in pieces of DNA from other places.
• Plasmids: foreign circular pieces of DNA in bacteria.