DNA and Genes Chapter 11

11-1 DNA: The Molecule of Heredity Objectives Analyze the structure of DNA Determine how the structure of DNA enables it to reproduce copies of itself SCS: B-4.1

What is DNA? What influences what an organism looks like? ◦ Environment ◦ Genes  Found in DNA (deoxyribonucleic acid)  Makes protein

Structure of DNA polymer of nucleotides (nucleic acid) composed of a phosphate group, sugar (deoxyribose), and a nitrogenous base

nucleotides come together held together by the phosphate groups at one end and by the bases in the middle

the structure resembles a ladder ◦ the bases make up the rungs and the sugar/phosphate group make up the sides of the ladder

◦ Each side is complimentary to each other

In 1953, Watson and Crick proposed the shape of DNA to be a double helix

Types of Bases Purines: Adenine (A) Guanine (G) Pyrimidines: Cytosine (C) Thymine (T)

The bases bond to each other in the center of the ladder with hydrogen bonds The bases bond together is a certain way – base pairing rule: A - T C - G The amount of A = T The amount of C = G

almost all organisms have the same bases A, T, C, G what makes organisms different is the sequence of these letters in your DNA

each species has a unique sequence of DNA some sequences are very similar – share a common ancestor

DNA Replication How do new organisms get the DNA of their particular species? DNA is copied or replicated during Interphase

Steps in Replication 1. Enzymes break down the hydrogen bonds holding the bases together – unzips molecule

2. Free floating complimentary nucleotides are added to the exposed strand with another enzyme. (base pairing rules apply)

3. Process continues until the entire molecule is unzipped and replicated

4. The end result are two copies of the DNA molecule. Each molecule has one strand from the original DNA and a complimentary copy.

11-2 DNA to Proteins Objectives

DNA codes for proteins Proteins help cells function

Proteins are made of amino acids The nucleotide sequence in DNA specifies the order of amino acids which make proteins DNA>>>>amino acids>>Protein

RNA – Ribonucleic Acid DNA can not leave the nucleus, so a copy has to be made - RNA the process of making a copy of DNA into RNA is called transcription

Detail of RNA (differing from DNA) Single strand of nucleotides Contains the sugar ribose Made of the 4 nucleotides A, C, G, and U (replaces T since thymine is not ever found in RNA)

Pairing Rules for RNA DNARNA A U T A C G G C

Types of RNA 1. mRNA or messenger RNA – copy of DNA that leaves the nucleus. 2. tRNA or transfer RNA – carries amino acids to the ribosome 3. rRNA or ribosomal RNA- part of the ribosome complex

Steps in Transcription 1. DNA is unzipped with enzymes exposing the specific region needed. 2. Free floating bases are added to growing strand of RNA along with ribose and phosphate groups

3. The RNA strand grows until it reaches a special stop signal 4. RNA drops off and leaves the nucleus to the site of protein synthesis – ribosomes 5. DNA zips back up.

Genetic Code mRNA carries the genetic message Message is made up of a language of nucleotides

◦ Uses bases for the alphabet of amino acids  Only 20 different amino acids are found ◦ A 3 letter (base) sequence codes for a particular amino acid ---- called a codon

 There are codons for stopping the reading of the sequence called stop codons (UGA, UAA, UAG)  The sequence always begin at a special start codon – AUG (aa – methonine)

◦ Use a “key” to determine what each codon codes for ◦ All organisms use this same “key” or chart to determine the amino acids

Translation Process of translating the mRNA sequence into amino acids to make proteins Takes place in ribosomes

Steps 1. mRNA attaches to ribosome 2. - tRNA molecule brings first amino acid to mRNA and attaches - tRNA contains the anticodon (compliment to codon on mRNA) -the ribosome slides to the next codon in the sequence

3. The next tRNA attaches to the mRNA along with its amino acid 4. When two tRNAs are in place, enzymes attach the two amino acids with a peptide bond 5. This process continues until a stop codon is reached on the mRNA

- The chain of amino acids now becomes a protein with a specific shape and function and goes where it is needed within the cell/body

Mutations

a change in the DNA a change in reproductive cells can only be passed on to the next generation changes can be bad, good, or have no affect at all

a change in body cells can not be passed on to the next generation can cause cancer or cell death

Types of Mutations 1. Gene level ◦ point mutation - change in a single base pair i.e. The dog bit the cat. Mutation The dog bit the car. changes the meaning of the “sentence” which can result in the wrong protein

◦ frameshift mutation-a single base pair is added. i.e. The dog bit the cat. Mutation The dob itt hec at.

2. Chromosome level change in actual chromosome due to nondisjuntion common in plants

Types Deletion- when part of the chromosome is left out Example: ABCDEFGH>>>>>> ABCEFGH

insertion- when part of a chromatid breaks off and attaches to its sister chromatid ABCDEFGH>>ABCBCDEF GH

inversion – when part of the chromosome breaks off and reinserts itself backwards Example ABCDEFGH>>>ADCBEFGH

translocation- when part of one chromosome breaks off and is added to a different chromosome Example: ABCDEFGH>>>WXABCDEFGH WXYZ>>>>>> YZ

Causes of Mutations mistake during replication Environmental, UV, chemicals, pollutants, radiation, high temperatures etc. are mutagens (agent which can cause change in DNA)

DNA does a remarkable job repairing itself