Transcript Ch 12- DNA and RNA

Ch 12- DNA and RNA
• Frederick Griffith carried out experiments to find out
how bacteria produce pneumonia
– Used mice and injected them with samples of bacteriaheat killed bacteria and harmless bacteria-no mice died
– Mixed the samples of bacteria and mice died from
pneumonia
• Transformation- process in which one strain of bacteria
is changed by a gene or genes from another strain of
bacteria
• Griffith hypothesized some factor was transferred from
the heat killed cells into the live cells- transforming
factor might be a gene
• Oswald Avery decided to repeat Griffith’s work in
1944
– Wanted to find which molecule in heat killed bacteria
was most important for transformation
– Made extract from heat killed bacteria, treated it with
enzymes that destroyed proteins, lipids,
carbohydrates and RNA- transformation still occurred
– Repeated experiment, used enzymes that would break
down DNA-transformation did not occur
• Avery and other scientists discovered that the
nucleic acid DNA stores and transmits the genetic
information from one generation of an organism
to the next
• Alfred Hershey and Martha Chase perform
experiment in 1952 using bacteriophages
– Bacteriophages- virus that infects bacteria,
composed of DNA or RNA core and a protein coat
– Used different radioactive markers to label the
DNA and proteins of bacteriophages
– The bacteriophages injected only DNA into the
bacteria, not proteins
• Hershey and Chase concluded that the genetic
material of the bacteriophage was DNA, not
protein
Components and Structure of DNA
• What is the overall structure of DNA molecule?
– DNA has a double helix, in which two strands are wound
around each other
– DNA is made up of nucleotides- made up of 3 parts;
deoxyribose molecule, phosphate group, and nitrogenous
base
• 4 kinds of nitrogenous bases in DNA
– Adenine, cytosine, guanine, thymine
• Base Pairing
– A=T and G=C--------always unless there is a mutation or
error
– Discovered by Watson and Crick
Sec 2- Chromosomes and DNA
Replication
• Where is prokaryote’s DNA found?
• Eukaryotes have as much as 1000 times more DNA than
prokaryotes
• Where is eukaryote’s DNA found?
• DNA molecules are very long and folded into tiny chromosomes
• Chromosomes contain both DNA and protein
• Chromatin- consists of DNA that is tightly coiled around proteins
called histones
• Nucleosome- beadlike structure made up of DNA and histone
molecules
– Fold enormous lengths of DNA into tiny space in nucleus
• Strands of nucleosomes are tightly coiled and supercoiled to form
chromosomes
DNA Replication
• DNA replication
– DNA molecules separates into two strands by helicases
– Then produces two new complementary strands following
the rules of base pairing
– Each strand of the double helix of the DNA serves as a
template, or model, for the new strand
• DNA replication is carried out by series of enzymes
– Enzymes unzip a molecule of DNA
– DNA polymerase- principal enzyme that is involved in
replication, proofreads each new DNA strand, polymerizes
individual nucleotides to produce DNA
• Video Clips for Biology!
• Animation Quiz 2 - DNA Replication Fork
Sec 3- RNA Protein Synthesis
• Genes- coded DNA instructions that control the
production of proteins within the cell
• DNA must be copied into RNA- they contain
coded information for making proteins
• Structure of RNA
– Consist of long chain of nucleotides made up of 5carbon sugar, phosphate group, and nitrogenous base
• Differences between DNA and RNA
– Sugar in RNA is ribose instead of deoxyribose
– Single stranded
– Contains uracil in place of thymine
Types of RNA
• What is the function of RNA?
– Protein synthesis
– Controls the assembly of amino acids into proteins
• 3 main types of RNA: messenger RNA, ribosomal
RNA, and transfer RNA
– Messenger RNA (mRNA)-carry copies of instructions
from DNA to rest of cell
– Ribosomal RNA (rRNA)- type of RNA that combines
with protein to make ribosomes
– Transfer RNA (tRNA)- transfers each amino acid to the
ribosome as it is instructed to by mRNA
Transcription
• Process in which RNA molecules are produced by copying part of
nucleotide sequence of DNA into a complementary sequence in
RNA
• How does this happen?
– 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
• How does RNA polymerase know where to start and stop making an
RNA copy of DNA?
– Will only bind to promoters- signals in DNA, have specific base
sequences
– Similar signals to stop transcription
• Video Clips for Biology!
• Tutorial 12.1 Transcription
Genetic Code
• Genetic code- known as the language of mRNA
instructions
• Codon- consists of three consecutive nucleotides that
specify a single amino acid that is to be added to the
polypeptide-64 possible
– UCGCACGGU- this sequence is read three bases at a time
• UCG-CAC-GGU- the codons represent the diff amino acids
– Serine-Histidine-Glycine
– Polypeptide- long chains made up of amino acids
• Start codon= AUG
• Stop codon= UGA, UAA, UAG
Translation
• Process in which a mRNA message is decoded into a polypeptide
chain
– Takes place on ribosomes
– Production of proteins
• What happens during translation?
– Messenger RNA is transcribed in the nucleus, and released into
cytoplasm
– Translation begins at AUG (start codon), as each codon of the mRNA
moves through ribosome, amino acid is brought into ribosome by
tRNA, amino acid is transferred to growing polypeptide chain
• tRNA has 3 unpaired bases (anticodon)- complementary to one mRNA codon
– Polypeptides join assembly line, continues until one of the three stop
codons is reached
– Protein synthesis
– Video Clips for Biology!
Sec 4- Mutations
• Mutations- changes in the genetic material,
mistakes during copying of DNA
• Gene mutations- changes in a single gene
– Point mutation- involving changes in one or a few
nucleotides, occur at single point
• Examples- substitutions- one base is changed to another
– Frameshift mutation- mutation that shifts the
“reading frame” of the genetic message by inserting
or deleting a nucleotide
• Examples- insertions and deletions- may change every
amino acid that follows point of mutation
• Chromosomal mutations- changes in the number or
structure of chromsomes
– May change locations of genes on chromosomes
– May change number of copies of some genes
• Examples
– Deletion- involves the loss of all or part of a chromosome
– Duplications- produce extra copies of parts of a
chromosome
– Inversions- reverse the direction of parts of chromosomes
– Translocations- occur when part of one chromosome
breaks off and attaches to another
Significance of Mutations
• Are all mutations harmful?
• Mutations may cause changes in protein
structure or gene activity- harmful
• Mutations are source of genetic variability in a
species- beneficial
• Cause of many genetic disorders
• Polyploidy- organism has extra sets of
chromosomes. What good is this?
– Polyploid plants are stronger and larger
Sec 5- Gene Regulation
• How does the cell determine which genes will
be expressed and which will remain “silent”?
• Gene appears as a confusing jumble of 4
letters- patterns within those letters
– Promoters- binding sites for RNA polymerase
– Start and stop signals for transcription
• Cells filled with DNA binding proteins that
help regulate gene expression
Gene Regulation
• Operon- group of genes that operate together
– In E. coli three genes are turned off and on together
to tell bacterium to use sugar lactose as food- lac
operon
– The lac genes are turned off by repressors and turned
on by the presence of lactose
• Operator- regulatory region on one side of
operon’s three genes
– Lac repressor, DNA binding protein, binds to O region
and prevents RNA polymerase- turns operon “off”
Eukaryotic Gene Regulation
• Principles of gene regulation between
prokaryotes and eukaryotes are pretty similarthere are some important differences
• Most eukaryotic genes are controlled individually
– Have regulatory sequences that are much more
complex than those of lac operon
• Why is gene regulation in eukaryotes more
complex than in prokaryotes?
– Cell specialization
Development and Differentiation
• Do cells in multicellular organisms just grow
and divide during embryonic development?
– Differentiation- cells become specialized in
structure and function
• Hox genes- series of genes that control the
differentiation of cells and tissues in the
embryo
– Careful control of expression in these genes is
essential for normal development