Modern Genetics

• DNA and RNA are made out of nucleotides
• the three nucleotides are phosphate, sugar (deoxyribose or ribose), and nitrogenous bases
• the four nitrogenous bases of DNA are adenine, thymine, guanine, and cytosine
• the four nitrogenous bases of RNA are adenine, uracil, guanine, and cytosine
• adenine pairs with thymine/uracil, and guanine pairs with cytosine
• DNA carries genetic information for the development of organisms
• DNA is located in the nucleus of a cell
• DNA has a double helix, while RNA has a single helix
• messenger RNA (mRNA) transports instructions from the nucleus to ribosomes
• transfer RNA (tRNA) brings amino acids to ribosomes
• ribosomal RNA (rRNA) makes up part of the structure of ribosomes
• RNA helps DNA make proteins
• sugar and phosphate make up the backbone of DNA and RNA
• purines are larger double ringed structures (guanine and adenine)
• pyrimidines are single, smaller ringed structures (cytosine, thymine, uracil)
• nitrogenous bases are bonded by hydrogen bonds and are complementary to each other
• the nitrogenous bases are covalently bonded to the backbone of DNA
• adenine is bonded to thymine by two hydrogen bonds
• guanine is bonded to cytosine by three hydrogen bonds
• to form a chromosome, the DNA is wrapped tightly around proteins called histones
• histones bead together and form nucleosomes
• DNA replication occurs during the synthesis phase of mitosis
• Since replication uses existing DNA as a template, it is semiconservative: each DNA molecule consists of an original strand and a new strand
• helicases are enzymes that untwists the DNA, separating it into two parental strands by the hydrogen bonds
• Primase is the enzyme that initiates the attachment of the new nucleotides and then DNA polymerase continues the process
• Ligase links new pieces of DNA onto the strand
• each triplet of nitrogenous bases is called a codon and each codon is a code for a specific protein
• when many amino acids are linked together, it creates a protein molecule
• messenger RNA travels from the nucleus to the cytoplasm (ribosomes) with the instructions for making proteins
• transfer RNA reads the message carried by mRNA and transfers the amino acids needed to a ribosome
• ribosomal RNA is found in the ribosome, used to bind mRNA and tRNA to the ribosome
• transcription is the process of forming a strand of RNA from a strand of DNA
• RNA polymerase is an enzyme that helps DNA to unwind and form mRNA
• promoter: a DNA sequence where RNA polymerase attaches and initiates transcription (5' to 3')
• terminator: signals the end of transcription
• after the mRNA is made it is modified (splicing)
• exons: parts of the RNA that codes for the proteins (involved)
• introns: part of the RNA code that is removed (cut out)
• when mRNA is formed, both the introns and exons are copied from the DNA template
• translation: the cell must translate the mRNA into an amino acid sequence (ribosome)