DNA and RNA Chapter 12 Hereditary Material Genes

DNA and RNA Chapter 12

Hereditary Material • Genes are protein codes. • Our genes are on our chromosomes. • Chromosomes are made up of DNA. • Genes are composed DNA!

Chromosome Structure • Chromatin is tightly coiled around proteins called histones. • DNA and histone molecules form a beadlike structure: nucleosome • Nucleosomes create the supercoils of DNA in a chromosome.

Chromosome Structure of Eukaryotes Chromosome Nucleosome DNA double helix Coils Supercoils Histones

Structure of DNA • In eukaryotes, DNA is found in the NUCLEUS of cells. • DNA is made up of a series of monomers called nucleotides. Nucleotide structure: 1. 5–carbon sugar: Deoxyribose 2. Phosphate group 3. Nitrogenous base • DNA is a twisted-ladder called a DOUBLE HELIX!

DNA Nucleotide Phosphate Group O O=P-O O 5 CH 2 O N C 1 C 4 Sugar (deoxyribose) C 3 C 2 Nitrogenous base (A, G, C, or T)

Nitrogenous Bases • Double ring PURINES Adenine (A) Guanine (G) A or G • Single ring PYRIMIDINES Thymine (T) Cytosine (C) T or C

Chargaff’s (Base Pairing) Rule Why do they pair together this way? • Adenine must pair with Thymine • Guanine must pair with Cytosine • The bases form weak hydrogen bonds T A G C

DNA Double Helix “Rungs of ladder” Nitrogenous Base (A, T, G or C) “Legs of ladder” Phosphate & Sugar Backbone

DNA Structure Nucleotide Hydrogen bonds Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

DNA Replication • Occurs during cell division. • Helicase enzyme “unzips” the molecule of DNA, breaking the hydrogen bonds. • Free-nucleotides in the nucleus will be bonded with its complementary base. • DNA polymerase helps to bond the nucleotides together and check for errors.

DNA Replication Section 12 -2 New strand Original strand DNA polymerase Growth Replication fork Nitrogenous bases Replication fork New strand Original strand

DNA Replication

The Scientists • Griffith – one strain of bacteria was “transformed” into another strain. • Avery – found that DNA was the transforming factor. • Hershey and Chase – DNA is the genetic material. • Watson and Crick – discovered the molecular structure of DNA.

Griffith’s “Transformation” Experiment

Avery’s experiment isolated the element that caused the bacterial to become lethal…DNA

Hershey-Chase Experiment Section 12 -1 Bacteriophage with phosphorus-32 in DNA Phage infects bacterium Radioactivity inside bacterium Bacteriophage with sulfur-35 in protein coat Phage infects bacterium No radioactivity inside bacterium

Chargaff and Franklin • Chargaff Percentages of guanine and cytosine bases are almost equal in any sample of DNA Same is true of adenine and thymine DNA in all instances and from all organisms followed this rule • Rosalind Franklin X-Ray diffraction showed that DNA was twisted into a double helix.

RNA and Protein Synthesis Section 12 -3

RNA • • • Long, single strand of nucleotides. Nitrogen bases: A, U, G, C no Thymine! Sugar: Ribose Found in cytoplasm and nucleus Types: messenger, transfer, ribosomal Function: Involved in the synthesis of protein molecules.

Protein Synthesis occurs in two phases: TRANSCRIPTION TRANSLATION

Transcription • Location where it occurs: Nucleus • RNA polymerase will unwind DNA at the region to be transcribed. • It locates and binds at the promoter.

• m. RNA is then made by base-pairing: A-U, G-C, T-A, C-G If DNA sequence is: GATTACA Then m. RNA sequence is: CUAAUGU • When finished, m. RNA leaves the nucleus and goes to the cytoplasm.

Section 12 -3 Transcription Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) RNA polymerase RNA DNA

Translation Location: Cytoplasm m. RNA finds a ribosome Ribosome reads strand for the start “codon” A codon is a m. RNA triplet. Ex: AUG, UUC, etc Start codon is: AUG Transfer RNA’s bring amino acids to ribosome.

Translation continued… • t. RNA’s anticodon bonds with m. RNA codons AUG UAA CGC t. RNA anticodons UAC AUU GCG • Amino acids connected with peptide bonds. • When a “Stop” codon is reached. Protein is released from ribosome.

Section 12 -3 Translation Animation

How to Interpret m-RNA’s Code: • Each 3 nitrogen base sequence is called a CODON. • Each codon specifies for a particular amino acid. • AUG codon starts the initiation of the protein and codes for the amino acid methionine. • Stop codons do not code for any amino acids ending the protein chain. • A polypeptide is a chain of amino acids joined with peptide bonds – aka a PROTEIN!

Codon Chart #1 Section 12 -3

Codon Chart #2

Let’s Practice! DNA: m. RNA: t. RNA: TACTTGGAT AUGAACCUA UACUUGGAU Amino Acid squence: Methionine, Asparagine, Leucine

Mutations Section 12 -4

Mutations • Changes that occur in the DNA • Two types: 1. Gene mutations 2. Chromosomal mutations • Many mutations are harmless • Pros: increase adaptation or survival • Cons: some can be lethal or debilitating

Gene Mutations • Changes that occur in a single gene. • Point mutations: one nucleotide that affects one amino acid. (substitutions produce point mutations) • Frameshift mutations: involve the reading of the DNA or m-RNA strand; many amino acids are affected. (insertion or deletions produce frameshift mutations)

Gene Mutations Frameshift mutations Point mutation: Substitution Insertion Deletion

Chromosomal Mutations • Whole chromosome is affected. • Four types: 1. Deletion – loss of material 2. Duplication – addition of material 3. Inversion – rearrangement of material 4. Translocation – switching material with another chromosome

Chromosomal Mutations Deletion Duplication Inversion Translocation