DNA and RNA Chapter 12

What is genetic material made of? Is it protein, carbohydrates, DNA… – Frederick Griffith determined that something transformed harmless (rough) strep bacteria into disease-causing (smooth) bacteria – Frederick Griffith determined that something transformed harmless (rough) strep bacteria into disease-causing (smooth) bacteria.

What transformed the bacteria? 1944 – Avery, MacLeod, and McCarty recreated Griffith’s experiment and tested the transformed bacteria – Avery, MacLeod, and McCarty recreated Griffith’s experiment and tested the transformed bacteria. Subjected to enzymes that broke down proteins, lipids, and carbohydrates….the bacteria still were transformed. Subjected to enzymes that broke down proteins, lipids, and carbohydrates….the bacteria still were transformed. When DNA-destroying enzymes were added, transformation failed to occur. When DNA-destroying enzymes were added, transformation failed to occur. DNA is found to be the genetic material. DNA is found to be the genetic material.

Avery, McLeod, and McCarty’s experiment

Confirmation by Hershey-Chase 1952 – Alfred Hershey and Martha Chase use bacteriophages (viruses) to confirm DNA is the hereditary material – Alfred Hershey and Martha Chase use bacteriophages (viruses) to confirm DNA is the hereditary material. They labeled phages with radioactive phosphorus and sulfur. (P is part of DNA) They labeled phages with radioactive phosphorus and sulfur. (P is part of DNA) The phages infected bacteria, they were dislodged using a blender and the material was analyzed… The phages infected bacteria, they were dislodged using a blender and the material was analyzed… Radioactive phosphorus was found inside the bacteria. Radioactive phosphorus was found inside the bacteria.

Hershey-Chase Experiment

What is DNA made of? Experiments determined that DNA is made of nucleotides: a deoxyribose (a sugar), a phosphate group, and one of four nitrogenous bases: Experiments determined that DNA is made of nucleotides: a deoxyribose (a sugar), a phosphate group, and one of four nitrogenous bases: Adenine (Purine) Adenine (Purine) Thymine (Pyrimidine) Thymine (Pyrimidine) Cytosine (Pyrimidine) Cytosine (Pyrimidine) Guanine (Purine) Guanine (Purine) But what is the structure?

Chargaff’s Rules Edwin Chargaff analyzed DNA in living things and found matching pairs. Edwin Chargaff analyzed DNA in living things and found matching pairs.

A and T, C and G, but what is the structure? 1950’s – Rosalind Franklin studied DNA using X-ray crystallography. 1950’s – Rosalind Franklin studied DNA using X-ray crystallography. Her photographs suggested DNA was twisted into a helix. Her photographs suggested DNA was twisted into a helix.

Watson and Crick’s DNA Model 1953 – James Watson and Francis Crick were working on a model of DNA, but couldn’t make it work – James Watson and Francis Crick were working on a model of DNA, but couldn’t make it work. Using Rosalind Franklin’s X-ray of DNA (without her knowledge or consent) they finally determined that DNA was a double helix, with bases connecting in the middle, and a phosphorus backbone. Using Rosalind Franklin’s X-ray of DNA (without her knowledge or consent) they finally determined that DNA was a double helix, with bases connecting in the middle, and a phosphorus backbone. They won the Nobel Prize. Rosalind Franklin died of cancer. They won the Nobel Prize. Rosalind Franklin died of cancer.

Watson and Crick’s Model

DNA – Deoxyribonucleic Acid

Where is DNA found in Cells? In Prokaryotes (bacteria), DNA is found in a closed loop in the cytoplasm. Stretched out it would be about 1.6 millimeters long! In Prokaryotes (bacteria), DNA is found in a closed loop in the cytoplasm. Stretched out it would be about 1.6 millimeters long! In Eukaryotes, DNA is found wrapped up tightly with chromatin around proteins called histones. Then condensed even more to form chromosomes. Chromosomes are only formed during cell division. If your DNA from one cell were stretched out, it would be over 1 meter long! In Eukaryotes, DNA is found wrapped up tightly with chromatin around proteins called histones. Then condensed even more to form chromosomes. Chromosomes are only formed during cell division. If your DNA from one cell were stretched out, it would be over 1 meter long!

SEM and Karyotype

DNA Replication In the G Phase of the cell cycle, DNA is not tightly coiled to allow for genes to be easily accessed. In the G Phase of the cell cycle, DNA is not tightly coiled to allow for genes to be easily accessed. In the S phase, DNA is replicated to prepare for cell division. In the S phase, DNA is replicated to prepare for cell division. An exact copy of all of the chromosomes must be made, without mistakes. An exact copy of all of the chromosomes must be made, without mistakes. The enzyme helicase unwinds the helix, and DNA polymerase attaches complementary base pairs and proofreads the new strands. The enzyme helicase unwinds the helix, and DNA polymerase attaches complementary base pairs and proofreads the new strands.

DNA Replication

Protein Synthesis The way you look (phenotype) is an expression of your genes (genotype). The way you look (phenotype) is an expression of your genes (genotype). Genes code for your cells to make specific proteins. Proteins make up your hair, muscle, skin, enzymes, etc. Genes code for your cells to make specific proteins. Proteins make up your hair, muscle, skin, enzymes, etc. When a specific protein is needed, a chemical signal is sent to your DNA to begin the process of making that protein. When a specific protein is needed, a chemical signal is sent to your DNA to begin the process of making that protein. Two steps: Transcription and Two steps: Transcription and Translation Translation

Transcription Transcription – from the words “across” and “write”, making a copy of the gene needed from the DNA template. Transcription – from the words “across” and “write”, making a copy of the gene needed from the DNA template. The promoter is a site on the DNA that tells the RNA polymerase where to begin copying the gene. The promoter is a site on the DNA that tells the RNA polymerase where to begin copying the gene. Messenger RNA (mRNA, ribonucleic acid) is created. Messenger RNA (mRNA, ribonucleic acid) is created. mRNA is complimentary, with thymine being replaced by uracil. mRNA is complimentary, with thymine being replaced by uracil.

Transcription After transcription, the RNA is edited. Introns are pieces that are cut out, and Exons are pieces that are kept. After transcription, the RNA is edited. Introns are pieces that are cut out, and Exons are pieces that are kept. Introns can allow for genetic variability. Introns can allow for genetic variability. Prokaryotes have very few introns. Prokaryotes have very few introns.

Translation After the mRNA is edited, it exits the nucleus through the nuclear pores. After the mRNA is edited, it exits the nucleus through the nuclear pores. Translation is the process by which the mRNA is “translated” into a protein. Translation is the process by which the mRNA is “translated” into a protein. Translation occurs in the cytoplasm on the ribosomes. (Ribosomes also have ribosomal RNA) Translation occurs in the cytoplasm on the ribosomes. (Ribosomes also have ribosomal RNA) mRNA is made up of codons, three base- pair sections. Examples: AUG, GCC. mRNA is made up of codons, three base- pair sections. Examples: AUG, GCC.

Translation At the ribosome, codons are paired with anticodons. At the ribosome, codons are paired with anticodons. Anticodons are complimentary bases which are part of transfer RNA (tRNA). Anticodons are complimentary bases which are part of transfer RNA (tRNA). Transfer RNA have amino acids attached to them. Amino acids are the building blocks of protein. Transfer RNA have amino acids attached to them. Amino acids are the building blocks of protein. At the ribosome, the amino acids are placed in order based on the mRNA code. As the protein chain grows, it is released. At the ribosome, the amino acids are placed in order based on the mRNA code. As the protein chain grows, it is released.

Translation

The Genetic Code

Mistakes in the Genetic Code Mutations – changes in the genetic material due to mistakes in copying, carcinogens, etc. Mutations – changes in the genetic material due to mistakes in copying, carcinogens, etc. Gene mutations – changes in a single gene Gene mutations – changes in a single gene Point mutations are changes in one or a few nucleotides. Examples: Substitutions, insertions, deletions Point mutations are changes in one or a few nucleotides. Examples: Substitutions, insertions, deletions Frameshift mutations are insertions or deletions that can affect the entire message. The entire protein can be ruined. Frameshift mutations are insertions or deletions that can affect the entire message. The entire protein can be ruined.

Mutations

Chromosome mutations When chromosomes are damaged, and large chunks are altered, major problems can occur. When chromosomes are damaged, and large chunks are altered, major problems can occur. Fragile X is an example of a gene mutation which causes a chromosome end to break off. Fragile X is an example of a gene mutation which causes a chromosome end to break off.

Gene Regulation Genes are not always “on” and making proteins. They are regulated. Genes are not always “on” and making proteins. They are regulated. An operon is a group of genes that regulate the protein production. An operon is a group of genes that regulate the protein production. Example: The lac operon is turned off by repressors and turned on by the presence of lactose. Therefore, lactase is produced when lactose needs to be broken down. Example: The lac operon is turned off by repressors and turned on by the presence of lactose. Therefore, lactase is produced when lactose needs to be broken down.