Chapter 12

 To understand genetics, scientists had to learn the chemical makeup of the gene.  Scientists discovered that genes are made of DNA  Scientists also found that DNA stores and transmits the genetic information from one generation of an organism to the next.  Scientists began studying DNA structure to find out how it carries info, decides traits, and replicates itself.

 DNA is a long molecule made up of units called nucleotides.  Each nucleotide contains a 5-carbon sugar, a phosphate group, and a nitrogen-containing base.  There are four kinds of bases in DNA:  Adenine (A)  Guanine (G)  Cytosine (C)  Thymine (T)

Green = 5-C sugar Peach = phosphate

 Watson and Crick made a 3-D model of DNA.  Their model was a double helix, in which two strands are wound around each other.  A double helix is like a twisted ladder  Sugar and phosphates make up the side of the ladder  Hydrogen bonds between the bases hold the strands together (the rungs)

 Aka the “base pairing rule”  Chargaff’s rule states that bonds only form between certain base pairs  A always pairs with T  G always pairs with C You must memorize this!!!!

 Most prokaryotes have one large DNA molecule floating in the cytoplasm.  Eukaryotes have DNA in the nucleus.  Amazing fact:  The nucleus of a human cell contains more than 1 meter of DNA!

 Contain both DNA and protein, which are tightly packed together to form chromatin.  Chromatin consists of DNA that is tightly coiled around proteins called histones.  This forms a beadlike structure called a nucleosome.  Nucleosomes pack with one another to form a thick fiber, which is shortened by a system of loops and coils.  Nucleosomes allow enormous amounts of DNA to fit into such a small region.

 Before a cell divides, it copies its DNA in a process called replication.  During replication:  The DNA molecule separates into 2 strands – each strand of the DNA molecule serves as a model for the new strand.  Following the rules for base pairing, new bases are added to each strand.  The end result is two identical strands.

 Its carried out by a series of enzymes  Some enzymes “unzip” the molecule of DNA – the hydrogen bonds between bases are broken  The two strands unwind and serve as templates to create two new strands  The key enzyme is called DNA polymerase – joins individual nucleotides to produce a DNA molecule  DNA polymerase is also involved in “proofreading” each of the new DNA strands to minimize errors.

Original Strand = T A C G T T New Strand = Original Strand = ATCGGCAATCACGAT New Stand = ATGCAA TAGCCGTTAGTGCTA

 Once upon a time in a land far, far away, there lived a beautiful but greedy queen named Queen Alicia. The Queen was good to the people who lived in her kingdom but she had something, something of great value to her and she would not share it with anyone. She had locked up in the tower of the nucleus a magical cookbook and this cookbook was filled with amazing recipes. The village was a happy one except for one problem. All they had to eat was mutton (mushy, fatty meat). One day a man named mRNA found out that the Queen was hiding the magic cookbook and he wanted to know the recipes. He found a way in through a hole called a nuclear pore. He crawled up to the very highest tower and found the cookbook. He started to transcribe the information when Queen Jen entered the chamber.

He ran out through another nuclear pore and ran through the fields of cytoplasm. He had a problem though. He could not cook, but he knew who could. He had heard of this amazing, very cool restaurant called the Ribosomal Café. The cook was notorious. He could even make mutton taste good. His name is rRNA. mRNA knew that RRNA was the man for the job. mRNA could do the recipes justice, but there was another problem. The cook only spoke French and mRNA only spoke English. So he had to find someone he could trust. He located the man named tRNA. tRNA was a translator, and could speak both English and French. He gave the recipes to tRNA and tRNA took them into the Ribosomal Café and gave them to chef rRNA who turned them into the most amazing food anyone in the village has ever eaten. After that you could always hear the chef singing “le poison, le poison, he he he, hu hu hu” and everyone lived happily ever after eating fish (protein).

 For a gene to work, the genetic instructions in the DNA molecule must be decoded.  The first step is to copy the DNA sequence into RNA.  RNA is a molecule which contains instructions for making proteins.

 RNA is similar to DNA, except for:  RNA contains the sugar ribose  DNA has deoxyribose  RNA is single-stranded  DNA is double stranded  RNA has uracil in place of thymine – A, U, C, G  DNA has A, T, C, G

 There are 3 kinds of RNA –  Messenger RNA (mRNA)  What is this in the story?  Has the instructions for joining amino acids to protein  Ribosomal RNA (rRNA)  What is this in the story?  Assembles the proteins  Transfer RNA (tRNA)  What is this in the story?  Carries each amino acid to the ribosome according to the coded message in mRNA  Contains an anticodon to pair up with mRNA Cookbook Cook Translator

 Process of making (or copying) RNA from DNA  Occurs in the nucleus  During transcription:  DNA strands are separated  RNA strand is built using one DNA strand as a template  DNA is transcribed (written) into RNA following base- pairing rules except that U binds to A  A  U, T  A DNA Strand = TACGCTACGCCTAATACT New mRNA Strand = AUGCGAUGCGGAUUAUGA

 The directions for making proteins are in the order of the four nitrogenous bases  This code is read 3 letters at a time  Each grouping of 3 letters is called a codon  AUG/CGA/UGC/GGA/UUA/UGA  Each codon stands for one amino acid  There is one “start” codon and 3 “stop” codons  Start = AUG  Stop = UGA, UAA, UAG

 Process in which the cell uses info from mRNA to make proteins  Takes place in the ribosome  How does it work?  mRNA moves into the cytoplasm and attaches to ribosome  As each codon of the mRNA moves through the ribosome, the proper amino acid is brought into the ribosome by tRNA.  The ribosome joins together each amino acid and the protein chain grows.  When the ribosome reaches a stop codon, the polypeptide chain is released.

 Use a Codon Chart

1. DNA Strand = TACGCTACGCCTAATACT 2. mRNA Strand = AUGCGAUGCGGAUUAUGA 3. Split into codons = AUG/CGA/UGC/GGA/UUA/UGA 4. Create Protein = Methionine -Arginine -Cysteine - Gylcine -Leucine

 Mutations are mistakes made when cells copy their own DNA.  Mutations are changes in the genetic material of a cell.  There are two types of mutations:  Gene mutations – changes in a single gene  Chromosomal mutations – change in the number or structure of chromosomes and affect multiple genes

 Point mutations (substitution)–  Occur at a single point in the DNA sequence  Causes one base to replace another, which only affects one amino acid  Frameshift mutations (insertion, deletion) –  A base is added or removed  All the codons are affected/changed resulting in a completely different protein

 Change in structure of chromosomes  Four types:  Deletions = ABC-DEF  AC-DEF  Duplications = ABC-DEF  ABBC-DEF  Inversions = ABC-DEF  AED-CBF  Translocations = ABC-DEF  ABC-JKL GH-IJKL GH-IDEF