chapter 12: dna and rna ferguson 2014 honors biology/chemistry

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Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

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Page 1: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

Chapter 12: DNA and RNA

Ferguson 2014Honors Biology/Chemistry

Page 2: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

DNA

• DNA is a long molecule made up of units called nucleotides.

• Each nucleotide is made up of 3 basic components:– 5-carbon sugar (deoxyribose)– Phosphate group– Nitrogenous base

Page 3: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• There are 4 kinds of nitrogenous bases in DNA:– Adenine– Thymine– Cytosine – Guanine

Page 4: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• Two scientists named Watson and Crick concluded that the shape of the DNA molecule was a double helix, in which two strands of DNA were wound around each other.

Page 5: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• The backbones of the double helix are formed by the sugar and phosphate groups of each nucleotide.

• The nitrogenous bases stick out sideways from each strand.

Page 6: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• Years before the double helix was discovered, a scientist named Edwin Chargaff discovered that:– The percentages of guanine (G) and

cytosine (C) are almost equal in any sample of DNA.

– The percentages of adenine (A) and thymine (T) are almost equal in any sample of DNA.

• This became known as Chargaff’s Rules

Page 7: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry
Page 8: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• Using Chargaff’s rule, Watson and Crick determined that hydrogen bonds could form only between certain bases, and provide just enough force to hold the 2 strands of the double helix together.

Page 9: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• The base-pairing rules became:– For every A (adenine) on one strand, there is

a T (thymine) on the other strand.– For every C (cytosine) on one strand, there is

a G (guanine) on the other strand.

The two strands are said to be “complementary”.

Page 10: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

Practice!• Following the base-pairing rules, write

the complementary strand of DNA for the given sequence of nucleotides:

• AAG CCA GAT AGT

Page 11: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

Building a DNA Molecule

• Black pentagons: Deoxyribose sugar• White tubes: Phosphate groups• Colored tubes: Nucleotides

– Orange: Adenine– Green: Thymine– Blue: Guanine– Yellow: Cytosine

Page 12: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• Build a single nucleotide containing the nitrogenous base adenine (orange).

• Now build a second nucleotide, but containing cytosine (yellow).

• Connect it’s phosphate group to the sugar of your first nucleotide. This is forming a sugar-phosphate backbone.

Page 13: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• Continue adding nucleotides until you have completed a strand following the code below:

A C T G G A T C T

• Once that single strand is completed, build a complementary strand.

• Connect the two strands with hydrogen bonds (white solid pegs).

• Twist the two strands to make a double helix.

Page 14: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

DNA Replication

• During DNA replication, the DNA molecule separates into two strands, and then produces two new complementary strands following the rules of base pairing.

• Each strand of the double helix serves as a template, or model for the new strand.

Page 15: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• Step 1: An enzyme called helicase “unzips” the double helix by breaking the hydrogen bonds between bases.

• The region where the two strands are splitting is called the replication fork.

Page 16: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• Step 2: A second enzyme, DNA polymerase, adds complementary nucleotides to each of the original separated strands.

• As DNA polymerase adds new nucleotides, it also “proofreads” to avoid any errors in base-pairing.

Page 17: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• Each strand of DNA has a 5’ end and a 3’ end, referring to the orientation of the 5-carbon sugar.

• The strands run anti-parallel to each other.

• DNA polymerase can only add to the 3’ end of a DNA strand.

Page 18: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• Leading strand: strand that reads 5’-3’• Replicated continuously.

• Lagging strand = strand that reads 3’-5’

• Creates fragments called “Okazaki Fragments” that are later connected by the enzyme ligase

Page 19: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• This process continues until the entire double helix has been replicated.

• The process is considered to be semi-conservative because each of the 2 new double helices contains one original strand and one newly synthesized strand.

Review Animation

Page 20: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

RNA and Protein Synthesis• Genes are coded DNA instructions that

control the production of proteins.• These genetic messages must first be

copied from DNA to RNA.• The RNA is then used to make proteins.

Page 21: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

Structure of RNA

• There are 3 main differences between DNA and RNA:– The sugar in RNA is ribose instead of

deoxyribose.– RNA is generally single-stranded.– RNA contains uracil in place of thymine.

Page 22: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry
Page 23: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

Types of RNA

• There are three main types of RNA:– messenger RNA (mRNA)– ribosomal RNA (rRNA)– transfer RNA (tRNA)

Page 24: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• Messenger RNA (mRNA) carries copies of instructions for assembling amino acids into proteins.

Page 25: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

Ribosomes are made up of proteins and ribosomal RNA (rRNA).

Page 26: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• During protein construction, transfer RNA (tRNA) transfers each amino acid to the ribosome.

Page 27: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

Protein Synthesis• The process of making proteins has two

steps:– Transcription– Translation

DNA strand(template)

TRANSCRIPTION

TRANSLATION

mRNA

Protein

Page 28: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

Transcription• Helicase separates the DNA double

helix, and an enzyme called RNA polymerase uses one strand of DNA as a template to make a single strand of mRNA.

• Regions called promoters determine which segment of DNA (which gene) the RNA polymerase will copy, or transcribe.

Page 29: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry
Page 30: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• RNA is formed using the same base-pairing rules discussed before, except that uracil has replaced thymine.

• “Transcribe” the following DNA strands into mRNA:

– AACTGACTTC

– GGATCCATCG

Page 31: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

RNA Editing• Some DNA within a gene is not needed

to produce a protein. These areas are called introns.

• The DNA sequences that code for proteins are called exons.

Page 32: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• As the mRNA leaves the nucleus, the introns are cut out of RNA molecules.

• The exons are the spliced together to form mRNA.

Page 33: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

The Genetic Code

• Proteins are made by joining amino acids into long chains.

• There are 20 different amino acids, and it is the unique combination of amino acids in your proteins that determine your genes.

• Amino acids are coded for by mRNA.

Page 34: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• A codon consists of three consecutive nucleotides on mRNA that specify a particular amino acid.

Page 35: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• There are 64 different 3-letter codons that only code for 20 amino acids.

• This means that more than one codon can code for the same amino acid.

• Some codons serve as a “stop” signal, and do not code for actual amino acids.

Page 36: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry
Page 37: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• Transcribe the following DNA strands into mRNA, and then translate the codons into amino acids using the wheel:

• DNA Strand 1: TAC GGC AGT

• DNA Strand 2: GAC TTT CCA

Page 38: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

Translation• Translation is the decoding of an

mRNA message into a polypeptide chain (protein).

• Translation takes place on ribosomes.

• During translation, the cell uses information from messenger RNA to produce proteins

Page 39: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• The ribosome binds new tRNA molecules and amino acids as it moves along the mRNA.

• Each tRNA molecule holds an anticodon that is complementary to a codon.

Page 40: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• As tRNA brings amino acids to the ribosome, the ribosome will form peptide bonds between the amino acids, forming a chain.

Page 41: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• This chain will grow until the ribosome reaches a stop codon, which triggers the release of the polypeptide chain.

Page 42: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• The completed polypeptide chain (protein) will be sent to the golgi body, where it will be packaged and shipped to its final destination.

Page 43: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

mRNA

DNA

Protein

Page 44: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

Transcription• Process by which

genetic information encoded in DNA is copied onto messenger RNA

• Occurs in the nucleus

• DNA mRNA

Translation• Process by which

information encoded in mRNA is used to assemble a protein at a ribosome

• Occurs on a Ribosome

• mRNA protein

Summary of Protein Synthesis

Page 45: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

Types of Mutations

• Mutations are changes in the genetic material.

• Gene mutations: involve changes in one or a few nucleotides, known as point mutations. – Substitutions– Insertions – Deletions

Page 46: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• Substitutions usually affect no more than a single amino acid.

Page 47: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• The effects of insertions or deletions are more dramatic.

• The addition or deletion of a nucleotide causes a shift in the grouping of codons.

• Changes like these are called

frameshift mutations.

Page 48: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

In an insertion, an extra base is inserted into a base sequence.

Page 49: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

In a deletion, the loss of a single base is deleted and the reading frame is shifted.

Page 50: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• Chromosomal mutations involve changes in the number or structure of chromosomes.

• Chromosomal mutations include deletions, duplications, inversions, and translocations.

Page 51: Chapter 12: DNA and RNA Ferguson 2014 Honors Biology/Chemistry

• Deletions involve the loss of all or part of a chromosome.

• Duplications produce extra copies of parts of a chromosome.

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• Inversions reverse the direction of parts of chromosomes.

• Translocations occur when part of one chromosome breaks off and attaches to another.