DNA, RNA & Protein Synthesis Chapters 12 & 13

The Structure of DNA

A little History Year Scientist(s) Discovery 1928 Frederick Griffith Bacteria transfer genetic material from cell to cell. 1944 Oswald Avery, Colin Macleod & Maclyn McCarty Griffith had discovered DNA! 1950 Erwin Chargaff Of the four possible nucloetides: As = Ts & Gs = Cs. 1952 Alfred Hershey & Martha Chase Genetic material in viruses is also DNA. Rosalind Franklin Demonstrated that DNA is a helix. 1953 James Watson & Francis Crick DNA is a double helix. 2000 Craig Venter & Francis Collins Sequenced human DNA.

DNA In prokaryotes (no nucleus), DNA is circular. In eukaryotes, DNA is on the chromosomes in the nucleus.

Structure of DNA Double-stranded helix Linked nucleotides

Nucleotide Parts Sugar - deoxyribose Phosphate group (has element phosphorous) Nitrogenous base Sugar and phosphate make the sides. Bases make the rungs.

Nucleotide Types Adenine (A) Thymine (T) Cytosine ( C ) Guanine (G) A bonds with T G bonds with C Called complementary base pairing

DNA Replication

DNA Replication When does it happen? Before cell division (mitosis or meiosis) Where does it happen? In the nucleus

DNA Replication: Step 1 Enzyme (DNA Polymerase) unwinds DNA

DNA Replication: Step 2 Enzyme attaches free nucleotides to the original strands until both strands are copied.

DNA Replication: Step 3 Replication occurs in many spots along the DNA until all parts are copied. Two identical strands are made. Now cell division can occur! http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/dna-rna2.swf

Replication in Different Cells In prokaryotes: Starts at a single point and proceeds in two directions until the entire chromosome is copied. In eukaryotes: Begins at many places and proceeds in two directions until the entire chromosome is copied.

RNA

Genes Section of DNA with the instructions to make 1 protein. Found in the nucleus.

Proteins Many amino acids linked together. Click here for animation -> XX Many amino acids linked together. Proteins are made in the cytoplasm.

Proteins are made in the cytoplasm by ribosomes, but the instructions for doing this (the DNA) can’t leave the nucleus.

A single-stranded copy of DNA. How can this work??? RNA A single-stranded copy of DNA.

DNA vs. RNA RNA DNA Chain of nucleotides. Sugar is ribose. Single-stranded. Bases are A,U,G,C. (U = uracil.) DNA Chain of nucleotides. Sugar is deoxyribose. Double-stranded. Bases are A,T,G,C.

Types of RNA Transfer RNA (tRNA) Messenger RNA (mRNA) Brings amino acid to the ribosome for protein assembly. Ribosomal RNA (rRNA) Inside ribosome. Helps with translation. Messenger RNA (mRNA) Copies DNA in the nucleus.

To go from DNA to a Protein, there are two steps: Transcription- mRNA makes copy of DNA Translation- protein is made from mRNA

Transcription: mRNA copies DNA Step 1: enzyme (RNA Polymerase) unwinds DNA promoter: regions of DNA where the enzyme binds Step 2: mRNA bases make a copy of DNA

Transcription (Part 2) Step 3: introns (bad bases) are removed, exons (good bases) are spliced together mRNA = AUACGUAC now = AUCUAC Step 4: cap and tail are added Step 5: mRNA leaves the nucleus for the cytoplasm. Link <- Click Here for Animation

Ribosomes & Protein Synthesis

Codons A section of three mRNA bases in a row that codes for one amino acid.

Anticodons The corresponding tRNA that carries the amino acid.

Translation: the mRNA is translated into a protein Animation<- Click Here for Animation -> XX 1.) Ribosome finds the start codon, AUG, on mRNA. 2.) The corresponding anticodon on the tRNA binds into place. 3.) The ribosome reads the next codon & its corresponding anticodon binds. 4.) The ribosome bonds the two amino acids on the tRNA together. The tRNA lets go. 5.) This continues until a stop codon is reached. Then the last tRNA & ribosome fall off. 6.) The amino acid chain folds into its proper structure.

The central dogma of molecular biology= DNA-> RNA-> protein gene expression: process by which a gene produces its product, which carries out its function

Gene Regulation & Expression

How do cells regulate gene expression? Proteins bind to sections of DNA that control transcription. More complex in eukaryotes because cells are specialized.

Differentiation When new cells become specialized in structure & function during embryonic development. In humans cells, this occurs 4 days after fertilization.

Mutations

What are mutations? Changes in the DNA sequence that changes the protein it codes for. Two Types: 1.) Chromosomal Mutations 2.) Gene Mutations

Chromosomal Mutations Result from changes in a whole chromosome. 1.) gene deletions 2.) gene duplications 3.) gene inversions 4.) translocations

Gene Deletion Parts of a chromosome break and rejoin, with a gene missing. Ex: Cris-du-chat Syndrome

Gene Duplication Most duplications have no phenotypic consequences.

Inversion Part of a chromosome becomes oriented in the reverse of its usual direction. Usually no phenotypic consequences.

Translocation Part of a chromosome breaks off and attaches to a nonhomologous chromosome. Can lead to nonviable zygotes.

Point Mutations Occur at a single point in the DNA. Usually one nucleotide is substituted for another, changing an amino acid. Ex: Sickle Cell Anemia

Frameshift Mutations Type of point mutation where an extra nucleotide is inserted or deleted, shifting the reading of codons, resulting in changes to ALL of the amino acids. Ex: Huntingdon’s Disease What is Mutation? The Outcome of Mutations-> Link

Mutagen An agent that causes a change in DNA. Ex: smoke, high energy radiation (X rays, UV light, nuclear radiation), chemicals (dioxins, asbestos, benzene, cyanide, formaldehyde), and high temperatures. Note: In some cases, a gene mutation may have positive effects leading to evolution.