Download Ch.12 - Jamestown Public Schools

Unit 4 Genetics
Ch. 12 DNA & RNA
Griffith & Transformation
 Griffith injected mice with 4 different
samples of bacteria
 When injected separately, neither heatkilled (disease-causing bacteria), nor
live, (harmless
bacteria) killed the
mice
Griffith & Transformation
 The 2 types injected together, however,
caused fatal pneumonia
 From this experiment, biologists
concluded (inferred) that genetic info.
could be transferred from 1 bacterium
to another
Griffith’s Experiment
Griffith & Transformation
 Transformation - when 1 strain of
bacteria is changed by a gene or genes
from another strain of bacteria
Avery & DNA
 Avery & other scientists performed
experiments to determine if
transformation required just 1 particular
molecule (of a gene)
 Discovered that the nucleic acid, DNA,
stores & transmits genetic info. from 1
generation of an organism to the next
The Hershey-Chase
Experiment
 Studied viruses, nonliving particles
smaller than a cell, that can infect living
organisms
 Bacteriophage - virus that
infects bacteria
The Hershey-Chase
Experiment
 They performed experiments with a
bacteriophage to determine its genetic
material
 They concluded that the genetic
material of the bacteriophage was DNA
& not protein
The Hershey-Chase
Experiment
The Components & Structure
of DNA
 Genes were known to do 3 specific
things:
 Carry info. from 1 generation to the next
 Put that info. to work by determining
heritable characteristics of organisms
 Be easily copied, since all of a cell’s genetic
info. is replicated every time a cell divides
The Components & Structure
of DNA
 DNA is a long molecule made up of
units called nucleotides
 Nucleotides - made up of 3 parts:
 A sugar
 A phosphate group
 A nitrogenous base
The Components & Structure
of DNA
 Watson & Crick developed the model of
DNA, a double helix, where 2 strands
were wound around each other
The Components & Structure
of DNA
 The 2 strands of DNA are held together
by hydrogen bonds
 Those bonds only link adenine (A) &
thymine (T), & guanine (G) & cytosine
(C)
 Base-pairing rule - A - T, G - C
Structure of DNA
DNA & Chromosomes
 Most prokaryotes have a single circular
DNA molecule in their cytoplasm
DNA & Chromosomes
 Eukaryotic DNA is located in the
nucleus, in the form of a # of
chromosomes
 The chromosome # varies from 1
species to another
DNA & Chromosomes
 Eukaryotic chromosomes have both
DNA & protein, packed tightly together
to form chromatin
 Chromatin - DNA that is tightly coiled
around proteins (histones)
DNA & Chromosomes
 From largest to smallest, genetic
information is arranged the following
way:
 Chromosomes
 Genes (found on chromosomes)
 DNA (makes up genes)
DNA Replication
 Each strand of DNA could be used to
make the other strand, they compliment
each other
 Replication - when a cell’s DNA is
copied
DNA Replication
 During DNA replication, the DNA
molecule separates into 2 strands, then
produces 2 new complimentary strands
following base pairing rules
 Each strand of the double helix serves
as a template, or model, for the new
strand
DNA Replication
 DNA polymerase - enzyme that joins
individual nucleotides to produce a DNA
molecule
 It also proofreads each new DNA
strand, to help prevent errors in copying
the DNA
DNA Replication
RNA & Protein Synthesis
 Genes - coded DNA instruc. that control
the production of proteins within the
cell
 The 1st step in decoding the genetic
messages is to copy part of the
nucleotide sequence from DNA into RNA
The Structure of RNA
 There are 3 main differences between
RNA & DNA:
 The sugar is a ribose, instead of
deoxyribose
 RNA is single-stranded
 RNA contains the nitrogenous base uracil
(U) instead of thymine (T)
Types of RNA
 There are 3 main types of RNA:
 Messenger RNA
 Ribosomal RNA
 Transfer RNA
Types of RNA
 Messenger RNA - (mRNA) - RNA
molecules that carry copies of
instructions for assembling amino acids
into proteins
 They serve as “messengers” from DNA to
the rest of the cell
Types of RNA
 Ribosomal RNA - (rRNA) - form of RNA
that combines with proteins to make a
ribosome
Types of RNA
 Transfer RNA - (tRNA) - RNA molecule
that transfers each amino acid to the
ribosome as it is specified by coded
messages in mRNA
Types of RNA
 Transcription - process of producing
RNA molecules by copying part of the
nucleotide sequence of DNA into a
complimentary sequence of RNA
 RNA polymerase - enzyme that works
similarly to DNA polymerase
Types of RNA
 During transcription, RNA polymerase
binds to DNA & separates the DNA
strands
 RNA polymerase then uses 1 strand of
DNA as a template to assemble
nucleotides into a strand of RNA
Transcription
The Genetic Code
 Proteins are made by joining amino
acids into long chains - polypeptides
 Each polypeptide has a combination of
any 20 different amino acids
The Genetic Code
 Codon - 3 consecutive nucleotides that
specify a single amino acid to be added
to the polypeptide
The Genetic Code
 For ex.:
 UCGCACGGU
 Read 3 at a time:
 UCG-CAC-GGU
 Which represents amino acids:
 Serine-Histidine-Glycine
The Genetic Code
Translation
 Translation - (protein synthesis) decoding an mRNA message into a
polypeptide chain (protein)
 It takes place on ribosomes
 Before translation occurs, mRNA is
transcribed (re-written) from DNA in the
nucleus & released in the cytoplasm
Translation
 Translation then begins when an mRNA
molecule in the cytoplasm attaches to a
ribosome
 As each codon of mRNA moves through
the ribosome, the proper amino acid is
brought into the ribosome by tRNA
Translation
 Each tRNA molecule has an anticodon 3 nitrogenous bases that are
complimentary to 1 mRNA codon
 The ribosome attaches 1 amino acid to
another, forming the polypeptide chain,
until it reaches the “stop” codon
Translation
 After the amino acid is attached, the
tRNA molecule that brought it into the
ribosome, is released back into the
cytoplasm
 The result is a protein
Translation
Translation
Summary: Role of RNA & DNA




Start with a single strand of DNA
That DNA is transcribed into RNA
The RNA is separated into codons
The codons code for amino acids, which
form a polypeptide chain
Genes & Proteins
 Many proteins are enzymes that
catalyze & regulate chemical reactions
 Genes for proteins can regulate the rate
& pattern of growth throughout an
organism
 Proteins are microscopic tools that are
designed to build or operate a living cell
Mutations
 Mutations - a mistake in the DNA base
sequence, may occur during copying
the DNA
 Changes in the genetic material
Kinds of Mutations
 Gene mutations are changes in a single
gene
 Chromosomal mutations are changes in
the whole chromosome
Gene Mutations
 Point mutations - change in 1 or a few
nucleotides, they occur at a single point
in the DNA sequence
 Frameshift mutations - adding or
deleting a nucleotide, shifts the
“reading frame” of the
genetic message
Chromosomal Mutations
 There are 4 types of chromosomal
mutations: deletions, duplications,
inversions, & translocations
 Deletions involve the loss of all or part
of a chromosome
 Duplications produce extra copies of
parts of a chromosome
Chromosomal Mutations
 Inversions reverse the
direction of parts of
chromosomes
 Translocations occur when
part of one chromosome
breaks off & attaches to
another
Significance of Mutations
 Mutations cause changes in protein
structure or gene activity
 They are the cause of many genetic
disorders
 Some are associated with many types
of cancer
Eukaryotic Gene Regulation
 Genes that code for liver enzymes are
not expressed in nerve cells
 Cell specialization requires genetic
specialization, but all cells in a
multicellular organism carry the
complete genetic code in their nucleus