3 In the middle of the 1900’s biologists were wondering how genes work In the middle of the 1900’s biologists were wondering how genes work. What they are made of, and how they determine the characteristics of organismIf the structures that carry genetic information could be identified, it might be possible to understand how genes control the inherited characteristics of living things
4 How does DNA do the following things? Carry info from one generation to the nextPut info to work by determining the inheritable characteristicsCopies itself, every time a cell divides
5 Nucleotides Units that make up DNA molecule Made of three parts 5 carbon sugar (deoxyribose)Phosphate groupNitrogen bases
11 The Double Helix Francis Crick & James Watson Trying to understand the structure of DNA by building modelsUnsuccessful until early 1953, Watson was shown a copy of Franklin’s X-ray pattern“The instant I saw the picture my mouth fell open and my pulse began to race.”James WatsonWithin weeks Watson and Crick had figured out the structure of DNAPublished their results in a historic one page paper in April of 1953
13 Watson and Crick later discovered what held the two strands together Hydrogen bonds could form between certain nitrogen bases and provide enough force to hold the two strands togetherHydrogen bonds could only form between certain base pairs adenine and thymine and guanine and cytosineThis principal is called Base pairingThis explains Chargaff’s Rule
18 To extract DNA for analysis, you need to know where to find it and how its organized DNA is located in the nucleusDNA is organized into chromosomes
19 Prokaryotic CellsProkaryotic cells have a single circular DNA molecule that contains nearly all of its genetic informationLocated in the cytoplasm
20 Eukaryotic Cells Much more complex 1000 times the amount of DNA as prokaryotesDNA is located in the nucleus in the form of chromosomes
21 Chromosome StructureQ: If eukaryotic DNA can contain a meter or more of DNA, how does it get packed in so tight into chromosomes?A: Eukaryotic chromosomes contain both DNA and protein that form a substance called chromatin
22 Histones Proteins that coil up DNA DNA + histone molecules form a bead-like structure called a nucleosomeNucleosomes pack together to form thick fibers that loop and coil together to form chromosomes
23 DNA coils around histones to form nucleosomes, which coil to form chromatin fibers. The chromatin fibers super coil to form chromosomes that are visible in the metaphase stage of mitosis.
25 DNA ReplicationWhen Watson and Crick discovered the double helix structure of DNA they recognized immediately how DNA could copy itselfThe strands are complementaryIf you could separate the two strands, the rules of base pairing would allow you to reconstruct the base sequence of the other strand
26 ReplicationWhen the DNA splits into 2 strands, then produces 2 new strands following the rules of base pairing
27 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.
28 How Replication Occurs UnwindingSynthesizingJoining
29 Getting StartedOrigins of replication- short stretched of DNA having a specific sequence of nucleotides.The place where DNA replication begins.Replication fork- Y-shaped region where the parental strands of DNA are being unwound.
30 1. Unwinding Replication is carried out by enzymes Before DNA replicates, the double helix must unwind and unzip.DNA Helicase-enzyme that is responsible for unwinding and unzipping the double helix.
31 1. UnwindingWhen the double helix unwinds/unzips the H+ bonds between the bases are broken, leaving single strands of DNA.Then, proteins called single-stranded binding proteins associate with the DNA to keep the strands separate during replication.As the helix unwinds, another enzyme, RNA Primase, adds a short segment of RNA, called RNA primer on each DNA strand.
32 1. UnwindingThe untwisting of the double helix causes tighter twisting and strain ahead of the replication fork.Topoisomerase- helps relieve this strain by breaking, swiveling, and rejoining DNA strands.
34 2. Synthesi zingWithin a bubble, the unwound sections of parental DNA strands are available to serve as templates for the synthesis of new complementary DNA strands.As the helix unwinds, another enzyme, RNA Primase, adds a short segment of RNA, called RNA primer on each DNA strand.
35 2. Base Pairing Also proof reads each new DNA strand DNA Polymerase: Joins individual nucleotides to produce a DNA molecule, which is a polymerThe nucleotides are added to the 3’ end of the new strand.Also proof reads each new DNA strand
36 2. Base PairingDNA polymerase continues adding new DNA nucleotides to the chain by adding to the 3’ end of the DNA strand.A binds with T / C binds with GThis allows for identical copies to be madeLeading Strand: elongated as the DNA unwindsContinuously added to 3’ endLagging Strand: elongates away from forkDone by adding small fragments. (Okazaki fragments)
37 3. JoiningWhen the DNA polymerase comes to an RNA primer on the DNA, it removes the primer and fills in the place with DNA nucleotides.When the RNA primer has been replaced, DNA ligase links the two sections.
40 Do Now Place the following steps of Replication in order. DNA UnzipsDNA unwindsSugar and phosphate groups form the side of each new strandThe bases attach from a supply in the cytoplasm
41 Do Now Place the following steps of Replication in order. DNA replication results in 2 DNA moleculesEach with two new strandsOne with two new strands and the other with two original strandsEach with one new strand and one original strandEach with two original strands1.DNA unwinds2.DNA Unzips3.The bases attach from a supply in the cytoplasm4.Sugar and phosphate groups form the side of each new strand
43 GenesCoded DNA instructions that control the production of proteins
44 DNA never leaves the nucleus, therefore the code must be copied into RNA, or ribonucleic acidThere are 3 main differences between RNA and DNAIt has the sugar ribose, instead of deoxyriboseRNA is single strandedRNA contains uracil in place of thymine
45 RNA is like a disposable copy of a segment of DNA RNA is like a working copy of a single gene
46 Types of RNA Messanger RNA (mRNA) Serve as messangers from DNA to the rest of the cell2. Ribosomal RNA (rRNA)Type of RNA that makes up parts of ribosomes3. Transfer RNA (tRNA)Transfers each amino acid to the ribosome as it is specified by the mRNA
48 TranscriptionRNA molecules are produced by copying part of the DNA sequence into RNATranscription requires an enzyme known as RNA polymeraseDuring transcription, RNA polymerase binds to DNA and separates the DNA strands. RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA.
49 Q: How does RNA polymerase “know” where to start and stop making a RNA copy of DNA? A: promotersSignals in DNA that indicate to the enzyme where to bind to make RNASimilar signals in DNA cause transcription to stop
52 RNA Editing Remember, a lot of DNA doesn’t code for proteins Introns – not involved in coding for proteinsExons – code for proteins
53 The introns get cut out of the RNA molecules before the final mRNA is made
54 The Genetic CodeProteins are made by joining amino acids into long chains called polypeptidesEach polypeptide contains a combination of any or all of the 20 different amino acidsThe properties of proteins are determined by the order in which different amino acids are joined togetherThe language of mRNA instructions is called the genetic code
55 The code is read three letters at a time Each 3 letter “word” is called a codonEach codon corresponds to an amino acid that can be added to the polypeptide
60 Steps of TranslationmRNA is transcribed from DNA in the nucleus and released into the cytoplasmmRNA attaches to a ribosome3. as each codon of the mRNA molecule moves through the ribosome, the proper amino acid is transferred to the growing amino acid chain by tRNAtRNA carries only one kind of amino acid and three unpaired bases called the anticodon
61 4. The amino acid chain continues to grow until the ribosome reaches a stop codon on the mRNA molecule
63 The Roles of RNA and DNAYou can compare the different roles played by DNA and RNA molecules in directing protein synthesis to the two types of plans used by builders. A master plan has all the information needed to construct a building. But builders never bring the valuable master plan to the building site, where it might be damaged or lost. Instead, they prepare inexpensive, disposable copies of the master plan called blueprints. The master plan is safely stored in an office, and the blueprints are taken to the job site. Similarly, the cell uses the vital DNA “master plan” to prepare RNA “blueprints.” The DNA molecule remains in the safety of the nucleus, while RNA molecules go to the protein-building sites in the cytoplasm—the ribosomes
64 Genes and ProteinsQ: If most genes contain nothing more than instructions for assembling proteins, what do proteins have to do with traits?A: Everything, proteins are microscopic tools designed to build or operate a component of a living cell
76 Significance of Mutations Most mutations don’t do anythingMutations that cause drastic changes in proteins produce defective proteins that disrupt normal biological activitiesMutations are also a source of genetic variability which can be beneficial
77 PolyploidyWhen plants produce triploid (3N) or tetraploid (4N) organismsThese plants are often larger and stronger