Chapter 12 Molecular Genetics

12.1 Vocabulary DNA – molecule that contains genetic information that is used in the development and functioning of all living organisms. Found in the nucleus and is the “code of life”. Nucleotide Double Helix Chromosome Nucleosome

Section 1 DNA: The Genetic Material Standards: 2.3, , 4.7 Objectives: Summarize the experiments leading to the discovery of DNA as the genetic material. Diagram and label the basic structure of DNA. Describe the basic structure of the Eukaryotic chromosome.

Discovery of DNA Fredrick Griffith (1928) – studied bacteria that causes pneumonia. – Strains can be transformed (or changed) into other forms. Oswald Avery (1944) – identified the specific molecule that transformed the R strain  S strain.

Discovery of DNA Alfred Hershey & Martha Chase (1952) – studied a bacteriophage (virus that attacks bacteria) by using radioactive labeling. – DNA & not protein is the transforming factor.

DNA Deoxyribonucleic Acid Genetic material found in the nucleus. – Also in the mitochondria & chloroplasts Contains instructions written in a chemical code – Determines all cellular functions – Influences how you look, develop, etc.

Structure of DNA Nucleotides are the building blocks of DNA. – 1 Nucleotide contains: 1 nitrogen base (A, T, G, C) 5 carbon sugar  deoxyribose 1 phosphate group

Structure of DNA James Watson & Francis Crick (1953) – discovered that DNA is a double helix. – Double helix – formed by two strands of nucleotides twisted around each other; twisted ladder shape or spiral staircase.

Structure of DNA The outer part of DNA is made of alternating molecules of phosphates and sugars  “Railings” The inner part of DNA is made of the nitrogen base pairs  “Steps” 4 Base Pairs – Adenine (A) – Guanine (G) – Thymine (T) – Cytosine (C)

DNA Structure Base Pairs (Cont’d) – Bases pair up in the middle of the DNA molecule following the BASE-PAIR RULE: Adenine always pairs with Thymine by 2 hydrogen bonds. Guanine always pairs with Cytosine by 3 hydrogen bonds. Purines ALWAYS bind to Pyrimidines “Complementary base pairing”

Base-Pairing Practice A = _____ T = _____ C = _____ G = _____ T = _____ C = _____

DNA Structure The two sides of DNA are oriented in opposite directions  Antiparallel – Like a two-lane road

Chromosome Structure DNA coils around histones (proteins) to form chromatin  creating a Nucleosome (repeating subunit of chromatin fibers, consisting of DNA coiled around histones) Chromatic supercoil to form chromosomes  X shaped

12.2 Vocabulary Semiconservative Replication DNA Polymerase Okazaki Fragment

Section 2 Replication of DNA Standards: 2.3, 4.3 Objectives: Summarize the role of the enzymes involved in the replication of DNA. Explain how leading and lagging strands are synthesized differently.

DNA Replication Semiconservative Replication – parental strands of DNA separate, serve as templates, and produce DNA molecules that have one strand of parental DNA and one strand of new DNA. – Process of copying DNA – Occurs in 3 Steps

Semiconservative Replication Step 1: Unwinding the Double Helix – DNA Helicase (an enzyme) unwinds and unzips DNA into two separate strands  H bonds break  leaving single strands of DNA. – Single-stranded binding proteins keeps strands separate during replication. – Primase (an enzyme) adds primer (short segments) on each DNA strand.

Step 1: Unwinding the Double Helix

Semiconservative Replication Step 2: Add New Base Pairs – DNA Polymerase (an enzyme) – catalyzes the addition of appropriate nucleotides to the new DNA strand. Adds new nucleotides to the old DNA molecule. Follows the base-pair rule: (A-T, G-C)

Semiconservative Replication Step 2: Add New Base Pairs (cont’d) Two new strands produced in different ways: – Leading Strand  new nucleotides added in a smooth, continuous motion. – Lagging Strand  new nucleotides added in small chunks called Okazaki Fragments and in a discontinuous motion. DNA Ligase (an enzyme) adds more bases to fill in the gaps between the Okazaki Fragments to make a continuous new DNA strand.

Step 2: Add New Base Pairs

Semiconservative Replication Step 3: Joining Base Pairs – DNA polymerase removes primer and fills in the place with nucleotides. – DNA ligase joins the sections to make each strand continuous. – At the end of replication  2 new strands of daughter DNA are produced. Each is made of ½ old DNA and ½ new DNA

DNA Replication Prokaryotes/Eukaryotes Prokaryotes Circular DNA strand is opened and replicated in only one section at a time. Replication occurs in two directions. DNA is shorter. Eukaryotes Opened and replicated in several sections at a time. Replication occurs in two directions. DNA is longer.

12.3 Vocabulary RNA Messenger RNA Ribosomal RNA Transfer RNA Transcription RNA Polymerase Codon Translation

Section 3 DNA, RNA, and Protein Standards: 2.2, 4.1, Objectives: Explain how messenger RNA, ribosomal RNA, and transfer RNA are involved in the transcription and translation of genes. Summarize the role of RNA polymerase in the synthesis of messenger RNA. Describe how the code of DNA is translated into messenger RNA and is utilized to synthesize a particular protein.

Why Proteins are Important DNA  “code of life” or “genetic code” because it contains the code for each protein that organisms need. Proteins (or protein messages) determine how an organism looks & functions.

Why Proteins are Important Gene – segment of DNA that contains instructions for making a protein. – Specific location on a chromosome – Controls inherited trait expression that is passed on for generations. Ribosomes make proteins

DNA  RNA Problem: DNA contains instructions for making proteins but DNA can’t leave the nucleus. Solution: RNA will take DNA’s instructions to the ribosomes for protein synthesis. RNA just speaks a different language than DNA.

RNA RNA is a nucleic acid called Ribonucleic Acid Single stranded Composed of nucleotides: – Sugar  Ribose – Phosphate Group – Nitrogen Bases: G bonds with C A bonds with Uracil NO (T)

RNA 3 Types of RNA: 1.mRNA (messenger RNA) – long strands of RNA formed complementary to one strand of DNA 2.rRNA (ribosomal RNA) – associated with proteins to form ribosomes in the cytoplasm 3.tRNA (transfer RNA) – small segments of RNA that transport amino acids to the ribosome

RNA

How Proteins are Made Part 1: Transcription (DNA  mRNA) – occurs in nucleus – gene for a specific protein is turned ON and that gene is copied into mRNA Example: (DNA) T A C G G T A (mRNA) A U G C C A U RNA Polymerase (an enzyme) – regulates RNA synthesis as DNA strand unwinds and unzips. – mRNA detaches and leaves nucleus and enters cytoplasm. TWO DNA strands rejoin.

Transcription

Transcription Practice 1.DNA C G T T A G C A A C T G mRNA 2. DNA A C G T C A A C G T T A mRNA

Genetic Code DNA codes for protein synthesis. DNA varies among organisms  base sequence is different. Proteins made up of amino acids 20 amino acids total Codon – 3 base code (N base) – 1 codon = 1 amino acid

Genetic Code

This section of DNA represents a gene. How many codons do you see in this gene? How many amino acids total make this protein?

Practice Converting mRNA  Amino Acids 1.AUG = 2.CUC = 3.AAG = 4.GGU = 5.UAC = 6.CAC = 7.CAA = 8.UGA = P. 338

How Proteins are Made Part 2: Translation (mRNA  Protein) – Occurs in cytoplasm – Interprets genetic message and builds proteins – mRNA attaches to a ribosome (rRNA) and is read 3 bases at a time (codon)

How Proteins are Made Part 2: Translation (continued) – tRNA is activated by an enzyme and carries amino acids to the ribosome & drops them off. 20 different types of tRNA molecules tRNA structure: – Anticodon site – 3 nucleotide base complementary to the codon of mRNA; end of tRNA molecule – Amino acid attached on other end

How Proteins are Made Part 2: Translation (continued) – Ribosome picks up amino acids and joins them together in a chain by peptide bonds  forming a protein. – Continues until STOP codon is read on the mRNA  last amino acid is added  protein breaks away from ribosome  protein synthesis ends.

The section of DNA you see here is a gene; – Use the mRNA you see here and the chart in your book to figure out which amino acid will go into this protein. Pg 338 DNAmRNAAmino acid TA Methionine (start) AU CG CG glycine CG GC TA isoleucine AU TA CG valine AU TA CG alanine GC AU AU stop TA TA

Translation

12.4 Vocabulary Gene Regulation Mutation Mutagen

Section 4 Gene Regulation and Mutation Standards: 4.8 Objectives: Summarize the various types of mutations.

Gene Regulation Gene Regulation – ability of an organism to control which genes are transcribed. – Transcription factors  controls what and when genes are expressed to make proteins. – 2 Transcription Factors: 1.Guide & stabilize the binding of RNA polymerase 2.Controls rate of transcription

Mutation Mutation – permanent change (or alteration) in DNA. – Changes vary from… One base pair (gene mutations)  large segments of DNA (chromosomal mutations) Beneficial  harmful (maybe lethal) Unnoticeable  disorders or death

Mutation If mutant cell is a body cell (somatic cell) then daughter cells can be affected but mutation will not be passed to offspring  aging and/or cancer. If mutant cell is a gamete (sex cell) then mutation will be transmitted to embryo and passed to offspring.

Types of Mutation Point Mutation – chemical change in one base pair (one nucleotide). – Missense Mutations (substitution) – codes for the wrong amino acid. Normal: AUG CAU UAC (histidine) Mutated: AUG GAU UAC (aspartate) – Nonsense Mutations (substitution) – change amino acid codon to a stop codon; terminates translation early  proteins can’t function normally Normal: AUG CAU UAC Mutated: AUG UGA

Types of Mutation Frameshift Mutations – change the “frame” of the amino acid sequence by adding or deleting nucleotides  changes the multiples of 3 codons. – Deletion Mutation – loss of a nucleotide Normal: AUG CAU UAC GUA Mutated: AUG AUU ACG UAU – Insertion Mutation – additions of a nucleotide Normal: AUG CAU UAC GUA Mutated: AUG CCA UUA CGU A

Types of Mutation Duplication Mutation – entire codon(s) repeat; changes the number of amino acids used. Normal: AUG CAU UAC GUA Mutated: AUG CAU CAU CAU CAU UAC GUA

How Mutations Occur Can occur spontaneously during (meiosis) replication  DNA polymerase may add the wrong nucleotide Mutagens – substances which cause mutations; certain chemicals and radiation. Most mutations repaired  no effect

Effects of Mutation The shape of a protein controls how it works. – Shape is determined by amino acids. Incorrect amino acids  change protein’s shape  protein may not work properly.