DNA, RNA, Chromosomes, and Inheritance

• DNA and RNA are fundamental to genetics and protein synthesis

Building Blocks of DNA & RNA

• Pyrimidines have a single-ring structure, examples in DNA & RNA are cytosine (C) and thymine (T).
• Purines have a double-ring structure; adenine (A) and guanine (G) are examples found in both DNA and RNA.
• Ribose and deoxyribose sugars differ in the presence or absence of a hydroxyl group at the 2' position.

Chromosomes

• Humans have 46 chromatids organized into 23 pairs within a cell's nucleus.
• Homologous chromosomes are pairs of chromosomes with the same genes.
• Autosomes: 22 pairs of chromosomes that control traits unrelated to gender.
• Sex chromosomes: the 1 pair of chromosomes that determine gender (chromosome 23).

Inheritance

• Passing genes down from one generation to another
• Gene: comprised of two alleles and are different versions of DNA; one is derived from each chromosome pair.

Human Karyotype

• A karyotype is a visual representation of all chromosomes within a cell.

Gene Mapping

• Amylase and Rh blood type are linked to chromosome 1.
• Gene blood type is associated with chromosome 9.
• Hemoglobin is linked to chromosome 11

Central Dogma of Molecular Biology

• Information is transferred from DNA to RNA to protein.
• Information cannot be transferred from protein back to protein or nucleic acids.

Transcription

• Transcription begins with a sequence of nucleotides in a gene which then determine the sequence of amino acids for a specific protein.
• Proteins are synthesized in the cytoplasm, but DNA is confined to the nucleus.
• Transcription involves the synthesis of mRNA in the nucleus, which then carries the genetic "message" to the cytoplasm.

Transcription Steps

• Initiation: RNA polymerase along with transcription factors recognizes and binds to the promoter region on the dna
• Elongation: RNA polymerase moves along the DNA template, synthesizing a complementary RNA strand.
• Termination: Transcription ends when the RNA polymerase reaches a termination sequence, releasing the RNA transcript.

Fine-Tuning Pre-mRNA

• Pre-mRNA has a short poly-A tail sequence at the 3' end.
• Pre-mRNA contains introns (non-coding sequences) and exons (coding sequences).
• Pre-mRNA has to undergo RNA processing before it can be translated.

Alternative Splicing

• Gene regulation in which mRNA can be spliced in multiple ways, creating different protein isoforms.
• There are 20,000-25,000 human genes which can code for up to 90,000 proteins due to alternative splicing.

Translation

• Translation requires mRNA, ATP, enzymes, ribosomes, and transfer RNA (tRNA).

Protein Composition

• Protein molecules are polypeptide chains made of 20 kinds of amino acids.
• The main job of a protein in cell is to fulfill its role as the work force of cell.
• Translation is the conversion from the nucleic acid language to the protein language.
• Nucleotide language uses an "alphabet" of 4 letters: A, U, C, and G.

RNA types

• Messenger RNA (mRNA): Carries genetic code from DNA to ribosomes.
• Transfer RNA (tRNA): Transfers amino acids to the ribosome for protein assembly.
• Ribosomal RNA (rRNA): A component of ribosomes

Ribosomes

• Ribosomes attach to mRNA and 'read' the bases three nucleotides at a time.
• A codon is a triplet of bases that codes for one amino acid.

Translation Process

• Translation is divided into three phases: initiation, elongation, and termination.

Translation: Elongation steps

• Codon recognition: The anticodon of an incoming tRNA pairs with the mRNA codon at the A site of the ribosome.
• Peptide bond formation: A polypeptide leaves the tRNA in the P site and attaches to the amino acid on the tRNA in the A site which catalyzes the bond formation between the two amino acids
• Translocation: The ribosome translocates, moving the tRNA with the growing polypeptide from the A site to the P site.

Termination

• Elongation continues until the ribosome reaches a stop codon
• At termination, the polypeptide is released
• The ribosome splits into its subunits for reuse

Mutations

• Mutations in genes lead to different versions, or alleles.
• Mutations are events, causing differing alleles in other families impacting many genes
• Repeated mutations lead to variations in a population.

Causes of Mutations

• Mutations can arise spontaneously when DNA replicates
• Mutations can be induced by exposure to radiation or certain chemicals (mutagens).

Somatic vs. Germline Mutations

• Somatic mutations occur in body cells and aren't passed on to offspring.
• Germ-line mutations appear in germ cells (egg and sperm) and can be transmitted to offspring.

X-linked Inheritance

• Red-green color blindness and hemophilia is linked to X-linked conditions.
• If a gene on the X chromosome has a dysfunctional allele, offspring will have X-linked conditions.
• Men are more likely than women to suffer from these conditions due to having one X chromosome

Genetic Traits

• Genes rarely act by themselves.
• Environmental factors and other genes influence genetic expression.
• Traits can be described as Mendelian (primarily due to a single gene), polygenic (primarily due to multiple genes), or multifactorial/complex (due to interaction between genes and the environment).