DNA and RNA

Introduction to DNA and RNA

• DNA is double stranded, RNA is single stranded
• DNA is located in the nucleus, while RNA is in the cytoplasm
• DNA has deoxyribose sugar, RNA has ribose sugar
• DNA's nitrogenous bases are adenine, thymine, cytosine, and guanine, while RNA has adenine, uracil, cytosine, and guanine
• In DNA, adenine pairs with thymine, and cytosine pairs with guanine
• In RNA, adenine pairs with uracil, and cytosine pairs with guanine
• There are three types of RNA including mRNA, rRNA, and tRNA
• Nucleotides are composed of a phosphate group, a sugar molecule, and one of four nitrogenous bases
• Messenger RNA carries genetic codes from DNA in the nucleus to ribosomes
• Ribosomal RNA accounts for 80% of total RNA and primarily stays in the ribosome
• Transfer RNA transfers amino acids during protein synthesis

DNA Replication

• Replication produces two identical DNA copies
• Helicase unzips the double helix by breaking hydrogen bonds
• Primase synthesizes short RNA primer sequences to start DNA synthesis
• Polymerase replicates DNA to build a new strand
• Ligase connects the two DNA strands together

RNA Transcription

• Transcription converts a region of DNA into mRNA
• DNA cannot exit the nucleus, so mRNA is needed to carry its message
• Ribonucleic acid polymerase binds and opens the DNA molecule for transcription
• RNA polymerase links free RNA nucleotides to the complementary DNA strand
• For example, if a DNA strand has the sequence CCG TTA CAT, the corresponding RNA sequence would be GGC AAU GUA
• After base pairing, the RNA molecule breaks away, and the DNA strands rejoin
• RNA then leaves the nucleus and enters the cytoplasm

RNA Translation

• Translation uses the nucleotide sequence of mRNA to determine the amino acid sequence of a protein
• Each set of three nucleotides in mRNA represents a codon, coding for one amino acid
• The mRNA binds to a ribosome, and tRNA molecules with specific amino acids approach
• A tRNA anticodon pairs with the first mRNA start codon AUG to form an initiation complex
• AUG codes for methionine and signals the start of protein synthesis
• Ribosomes then slide along the mRNA to the next codon
• A new tRNA molecule carrying an amino acid pairs with the second mRNA codon
• An enzyme forms a peptide bond between the first and second amino acids
• The process continues until the ribosome reaches a stop codon (UAA, UAG, UGA)
• During this time, a chain of amino acids is formed
• Finally, the polypeptide chain is released and protein synthesis is complete

Biomolecules

• Biological macromolecules include carbohydrates, lipids, proteins, and nucleic acids
• They have various functions, such as energy storage and protection
• Food is a source of molecules needed for life

Carbohydrates

• Carbohydrates are the main source of energy
• Classified as either simple or complex, they provide protection and form shells/exoskeletons
• Another term for carbohydrate is saccharide
• Monosaccharides include glucose, galactose, and fructose
• Disaccharides include maltose, sucrose, and lactose
• Polysaccharides include starch/amylose, amylopectin, glycogen, and cellulose

Lipids

• Lipids are important nutrients
• Overconsumption of unhealthy fats can cause heart disease, cancer, and obesity
• Lipids are material for cell membranes, provide insulation, aid in digestion, and act as signal molecules
• Lipids are classified as triglycerides, phospholipids, waxes, and steroids
• Fats are solid triglycerides from animal sources
• Oils are liquid triglycerides from plant sources
• Animal fats contain high percentages of saturated fatty acids
• Plant oils contain mostly unsaturated fatty acids

Proteins

• Proteins are formed of carbon, hydrogen, oxygen, and nitrogen
• Sulfur and other metals can also be found in proteins
• Proteins consist of amino acids

Protein Examples & Functions

• Keratin is a structural protein found in hair, skin, and nails
• Fibroin is a silk protein with smooth texture and high resistance to deformation
• Collagen is a fibrous protein in connective tissues
• Enzymes catalyze chemical reactions by speeding them up, lowering needed energy, or binding substances

Enzymes

• Lipase helps in the digestion of fats
• Pepsin helps in breaking down proteins into peptides
• Sucrase, also called invertase, helps in the digestion of sugars and starches
• Myoglobin, a polypeptide in muscles, stores oxygen

Nucleic Acids

• Nucleic acids store, transfer, and express genetic information
• Friedrich Miescher discovered nucleic acids in 1868
• Nucleic acids contain carbon, hydrogen, oxygen, nitrogen, and phosphorus
• DNA (deoxyribonucleic acid) carries genetic code
• DNA is the blueprint of life
• RNA carries information from DNA to synthesize proteins
• Nucleic acids consist of nucleotides, also known as polynucleotides

Nucleotides

• A nitrogenous base
• A five-carbon carbohydrate or sugar
• A phosphate group