DNA: Replication and Central Dogma

DNA: Replication and The Central Dogma

• DNA is a double helix resembling a twisted ladder.
• The sides of DNA are composed of alternating sugar and phosphate molecules.
• The rungs of the ladder are pairs of four types of nitrogenous bases.
• DNA is antiparallel: The two strands run in opposite directions.
• Each strand of DNA is complementary to the other: The sequence of one strand can be determined from the other.
• The Central Dogma explains the flow of genetic information in cells.
• DNA replicates, resulting in copies of the original DNA sequence.
• Genetic information is passed from DNA to DNA, preserving and transmitting information between generations.
• DNA's information is expressed into proteins in two steps: transcription and translation.
• Transcription: DNA transcribed into RNA (transcriptome).
• Translation: RNA translated into Protein (proteome).

DNA Structure

• Deoxyribose sugar in DNA is a single-ring pentose sugar with a hydroxyl (-OH) group on the 2' carbon.
• The nitrogenous bases in DNA are adenine (A), thymine (T), guanine (G), and cytosine (C).
• Adenine pairs with Thymine through two hydrogen bonds.
• Cytosine pairs with Guanine through three hydrogen bonds.
• Phosphodiester Bond: Covalent bond that links the 3’ carbon atom of one sugar molecule to the 5’ carbon atom of another.
• The 3' end of DNA contains a free hydroxyl group, while the 5' end has a phosphate group.

RNA Structure

• Ribose sugar in RNA is a single-ring pentose sugar with a hydroxyl (-OH) group on the 2' carbon.
• The nitrogenous bases in RNA are adenine (A), uracil (U), guanine (G), and cytosine (C).
• Uracil is only found in RNA and replaces thymine.
• RNA is single-stranded and shorter than DNA.

Gene Expression and Transcription

• Transcription: The process of copying a DNA sequence into mRNA.
• The DNA double helix unwinds near the gene being transcribed, forming a transcription bubble.
• Transcription occurs in three stages: initiation, elongation, and termination.
• Transcription uses one of the two DNA strands as a template, creating an RNA sequence that is complementary to it.
• The template strand is also called the non-coding strand.
• RNA polymerase: The enzyme that synthesizes RNA using the template strand.
• RNA polymerase binds to a promoter region on the DNA, signaling the start of transcription.
• Transcription continues until RNA polymerase reaches a terminator sequence, signaling the end of transcription.
• Post-transcriptional modification: The newly transcribed RNA molecule undergoes modifications, such as splicing and capping, before it can be translated into protein.

RNA Interference

• RNA interference (RNAi): A process by which short RNA molecules interfere with gene expression.
• Small interfering RNAs (siRNAs): Short RNA molecules that bind to complementary sequences in mRNA and tag it for degradation.

Human Genome

• The human genome is the complete set of genetic material in a human cell.
• It consists of approximately 3 billion DNA base pairs.
• The human genome is organized into 23 pairs of chromosomes, for a total of 46 chromosomes.
• Autosomal chromosomes: The 22 pairs of chromosomes that are not sex chromosomes.
• Sex chromosomes: The pair of chromosomes that determine sex (XX for female, XY for male).
• Homologous chromosomes: Pairs of chromosomes that contain the same genes, but with potentially different alleles.
• Somatic cells: All body cells except reproductive cells.
• Gametes: Reproductive cells (sperm and egg).
• Diploid (2n): Having two sets of chromosomes (one from each parent).
• Haploid (n): Having one set of chromosomes.
• Genotype: The genetic makeup of an organism.
• Phenotype: The observable characteristics of an organism.

Cell Cycle

• Cell cycle: The series of events that a cell goes through from its formation to its division into two daughter cells.

Mutations

• A mutation is a change in the nucleotide sequence of DNA.
• Mutations can occur due to errors in DNA replication or damage caused by environmental factors.
• Mutations can alter the amino acid sequence of protein, potentially affecting its function.
• Mutations can be beneficial, harmful, or neutral.

Point Mutations

• Point mutation: A change in a single nucleotide in a DNA sequence.
• Silent mutation: A point mutation that does not change the amino acid sequence of the protein.
• Missense mutation: A point mutation that changes the amino acid sequence of the protein.
• Nonsense mutation: A point mutation that introduces a premature stop codon into the mRNA sequence, resulting in a truncated protein.

Explore the intricate structure of DNA and the processes of replication and the Central Dogma. This quiz covers the key concepts of how genetic information flows from DNA to RNA to proteins, as well as the relationship between DNA strands. Test your understanding of transcription and translation as fundamental steps in expressing genetic information.