Understanding Genes and DNA Structure

The Importance of Genes

• Genes carry information through generations, holding information for traits.
• Genes are made of DNA (Deoxyribonucleic Acid) sequences.
• DNA molecules consist of nucleotides.
• Nucleotides contain a phosphate group, a 5-carbon sugar (deoxyribose), and a nitrogen base.
• Without genes, bodies would lack necessary information and genes are vital for producing proteins and regulating cell growth.

DNA Structure

• DNA exists as a double helix, composed of a coding strand and a complementary strand.
• The coding strand gives instructions, while the complementary strand is its complement.

Nucleotide Structure

• Nucleotides have 3 parts including, a phosphate group, a pentose sugar, and a nitrogenous base.

DNA Structue: Double Helix

• The double helix describes DNA's physical structure, made of two linked nucleotide strands twisted together.

Nitrogenous Bases

• Nitrogenous bases are categorized into purines (adenine and guanine) and pyrimidines (thymine, cytosine, and uracil).
• Uracil is exclusive to RNA.
• Base pairing rules: Adenine (A) pairs with Thymine (T) in DNA, becoming Uracil (U) in RNA; Guanine (G) pairs with Cytosine (C).

DNA Replication Steps

• Helicase unzips the "parent DNA strand," with SSB proteins keeping the strands separated.
• Primase adds an RNA primer to signal DNA polymerase where to begin building the new DNA strand.
• DNA polymerase builds new DNA strands, with Ligase "gluing" Okazaki Fragments.
• Okazaki Fragments are created due to the 5' to 3' direction requirement for DNA polymerase, causing gaps on the lagging strand, which Ligase then fills.

Enzyme Involvement in DNA Replication

• Helicase breaks the weak hydrogen bonds between the double helix, functioning as "The Unzipper."
• Primase creates the primer (made of RNA), guiding DNA polymerase on where to start building new DNA, thus being "The Primer."
• DNA Polymerase replicates DNA molecules to build a new DNA strand, serving as "The Builder."
• Ligase joins the two strands and creates hydrogen bonds between them, acting as "The Gluer."

Mutations

• A mutation involves a change in the base sequence of DNA.
• Chromosomal mutations occur if a chromosome is damaged or does not separate properly.
• Mutations result from DNA replication errors or chemical mutagens' effects.
• Chemical mutagens, react with DNA and alter individual nucleotide structures.

Types of Mutations

• Insertion: A nitrogen base addition to a DNA strand which can lead to a frameshift mutation.
• Deletion: A nitrogen base removal from a DNA strand which can cause a frameshift mutation.
• Substitution: A nitrogen base replacement with a different base which leads to a missense, silent, or nonsense mutation.

How Mutations Affect DNA

• Silent mutations do not impact coded amino acid.
• Nonsense mutations cause a premature start/stop, altering the final amino acid sequence length.
• Missense mutations only change one amino acid after a nitrogen base substitution.
• Frameshift mutations shift the reading frame, altering the amino acid sequence in the mutated DNA.

Factors That Increase Mutation Risk

• Increased mutation risk factors include ionizing radiation (UV-light and gamma rays), chemical mutagens (alcohol or tar), and certain viruses/disorders.
• These factors can integrate into DNA, causing damage or structural changes.

Codons

• Codons are a string of three nucleotides forming a genomic information unit.
• Each codon directs the cell to start a new protein strand's creation.
• Codons, consisting of Guanine, Adenine, Thymine, and Cytosine, create amino acid strands.
• Codons serve as the genetic code for everything with a protein.
• Mistakes in codons can lead to mutations.

Protein Synthesis

• Helicase unzips the original DNA strand.
• mRNA is created complementary to the original DNA coding strand, replacing Thymine with Uracil.
• The mRNA is carried out of the cell.
• tRNA codons are created as a complement to the mRNA strand, bringing in the correct amino acids.
• Each codon corresponds to one amino acid.
• One codon equals 3 mRNA nitrogen bases.

Amino Acids

• Amino acids serve as buildings blocks of proteins.
• Different amino acid combinations create different proteins.
• Amino acids consist of three codons, with each triplet corresponding to an amino acid.

mRNA vs tRNA

• tRNA is a special RNA that brings amino acids to the ribosome.
• tRNA is read from 3' to 5'.
• tRNA binds to another amino acid and can be used in a protein-making process later.
• tRNA cannot enter the cell nucleus.
• tRNA has two regions, one pairing with mRNA and the other combining with a specific amino acid.
• Thymine becomes Uracil in tRNA.
• mRNA goes to the cytoplasm and ribosome.
• mRNA transports instructions for making proteins
• mRNA travels from the cell's nucleus to the cytoplasm.
• mRNA is the complementary strand of the original DNA.
• mRNA is a messenger from the DNA code to the ribosomes.
• mRNA is read in a 5' to 3' direction.

DNA Repair

• DNA repairs itself to maintain genetic information for transfer and prevent cancerous growth.
• DNA repair is crucial for sustaining life, preventing dangerous mutations from UV damage.