Chapters 16 and 17. Before the end of the semester we will be covering… Historical DNA experiments...
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DNA, RNA, and Protein Synthesis Chapters 16 and 17
Chapters 16 and 17. Before the end of the semester we will be covering… Historical DNA experiments Structure of DNA/RNA DNA Replication Protein Synthesis
Before the end of the semester we will be covering Historical
DNA experiments Structure of DNA/RNA DNA Replication Protein
Synthesis (Transcription and Translation) Mutations Gene Expression
(if time) No more labs this semester! Your final will be
comprehensive Both multiple choice and short answermore info to
come!
Slide 3
Important Historical Experiments In the 1940s little was
understood about inheritance and how it worked. It was believed the
genetic material was either DNA or protein. It was understood that
chromosomes are made of both DNA and protein Initial experiments
suggested it was proteinlittle was understood about DNAs structure
or function (proteins were identified as being more complex)
Slide 4
Avery, McLeod, McCarty 1944 goal was to identify if inherited
substance was either DNA, RNA, or protein used chemicals and
bacteria that only allowed one of the above to be active at a time
Results determined that the transforming agent was DNA Scientific
community still skeptical
Slide 5
Hershey and Chase 1952 used bacteriophages to confirm DNA is
the genetic material bacteriophages were tagged with radioactive
isotopes (DNA--P; protein--S) it was shown that the DNA was able to
infect the bacteriophages, not the protein by tracking the
radioactivity
Slide 6
Watson and Crick 1953 discovered the shape of DNA molecule was
a double helix using pictures of the molecule, they built a model
sugar/phosphate backbone nitrogen bases in the interior strands are
antiparallel helix uniform in diameter (base-pairing rules)
Slide 7
Wilkins and Franklin 1953 Franklin used x-ray diffraction to
photograph DNA (her pictures were used by Watson and Crick) Wilkins
was working closely with Franklin in her lab and allegedly showed
Watson and Crick the photograph that helped them build their model
Watson, Wilkins, and Crick were awarded the Nobel Prize for science
in 1962. Rosalind Franklin died in 1958 of cancer and was never
given a Nobel Prize.
Slide 8
Using the original papers published in Nature in 1953, identify
the characteristics of a DNA molecule. What important
characteristics did they (Watson, Wilkins, Crick, and Franklin)
discover? List/highlight as many as you can.
Slide 9
Deoxyribonucleic Acid (DNA) Classified as a nucleic acid
(biological molecule) Genetic material organisms inherit from their
parents Copied prior to cell division (mitosis/meiosis) Shape of a
double helix Made up of nucleotides (building blocks) 5-carbon
sugar (deoxyribose), phosphate, nitrogen base
Slide 10
Base-Pairing Rules: A T C G Directionality Complementary
strands Antiparallel: each strand runs in an opposite direction
Designated 5 and 3 ends (carbon on sugar) Two types of bases
Purines: two carbon rings Guanine, Adenine Pyrimidines: one carbon
ring Cytosine, Thymine, Uracil
Slide 11
Ribonucleic Acid (RNA) mRNA (messenger RNA)instructions (from
DNA) for making protein tRNA (transfer RNA) carries amino acids
rRNA(ribosomal RNA)makes up ribosomes 5-carbon sugar (ribose)
Single stranded (one gene) Uracil instead of thymine A U
Slide 12
Both RNA and DNA Have adenine, cytosine, and guanine Made of
nucleotides Sugar and phosphate backbone Nitrogen bases
perpendicular to backbone Held together by hydrogen bonds
Slide 13
Biochemical Gymnastics: DNA Replication Occurs during S-phase
of Interphase in the cell cycle Semi-conservative process. Each new
strand of DNA produced is made of one parental and one new strand
(described by Watson and Crick) Each strand serves as a template
for the new strand In prokaryotes DNA is circular In eukaryotes DNA
is linear
Slide 14
DNA Replication (Overview) Begins at the origin of replication
(specific sequences of DNA nucleotides) Proteins recognize this
sequence and attach to the DNA and separate the two strands
creating a bubble At either end of this bubble is the replication
fork Replication then proceeds in both directions from the origin
until both strands are copied. In prokaryotes replication starts in
one spot, in eukaryotes multiple spots
Slide 15
The Players. Helicase: enzyme that unwinds and unzips the helix
at the replication forks. Single-strand Binding Protein (SSBPs):
binds to unpaired DNA strand to keep them from re-pairing
Topoisomerase: enzyme that relieves tension ahead of the
replication fork (from untwisting of strand) Primase: enzyme that
synthesizes the RNA primer for replication DNA Polymerase: several
enzymes that catalyze the synthesis of new DNA (in eukaryotes there
are 11 total); also checks for errors Ligase: links new fragmented
DNA segments together
Slide 16
Replication only occurs in the 5 to 3 direction Nucleotides
added only to 3 end of molecule This is problematic for one side of
the DNA molecule Leading strand: continuous strand Single RNA
primer Lagging strand: discontinuous in fragments (Okazaki
fragments) multiple RNA primers
Slide 17
The steps 1. Origin of replication is located 2. Bubble forms
in DNA helix by Helicase 3. Primase synthesizes primer to begin
replication Need RNA primer to have something to add nucleotides
to. 4. DNA Nucleotides are added by DNA polymerase to primer to
begin new strand 5. Replication proceeds in the 5 to 3 direction on
both sides of the molecule Leading and lagging strands 6.
Replication continues until the entire molecule is copied
http://highered.mheducation.com/sites/0035456775/student_view0/chapter12/dna_replication.html
http://www.dnalc.org/resources/3d/04-mechanism-of-replication-advanced.html
Slide 18
Ending Replication After every round of replication some of the
DNA molecule is lost due to polymerase not being able to replicate
it. To avoid excess loss of DNA, the ends of eukaryotic chromosomes
have telomeres (long repeating sequences) Excess DNA nucleotides
(no genetic info) Acts as a buffer to actual genes (does shorten
over time thought to be evidence of aging)
Slide 19
Chapter 18
Slide 20
Gene Expression: process by which DNA directs the synthesis of
proteins occurs in two parts: Transcription and Translation this
process dictates the presence of specific traits
(genotype/phenotype) occurs in all organisms Watson and Crick
describes this as the central dogma (DNA RNA Protein)
Slide 21
Transcription synthesis of RNA (mRNA) using DNA as a template
(protein instructions) occurs in nucleus (eukaryotes) or cytoplasm
(prokaryotes) Prokaryotes can begin translation before
transcription is finished Eukaryotes have an extra step during
transcription before translation can begin
Slide 22
DNA is a template strand, which is used to produce mRNA
instructions (for protein) mRNA is complementary to DNA uses
different nucleotides (uracil) RNA polymerase unzips DNA and joins
complementary RNA nucleotides to copy instructions reads 5 to 3, no
primer needed promoter: DNA sequence where RNA polymerase attaches
and initiates transcription http://www.dnalc.org/resources/3d/13-
transcription-advanced.html
Slide 23
3 Stages Initiation RNA polymerase joins to the promoter and
begins to unwind helix helped by transcription factors (proteins),
creates a transcription-initiation complex Elongation RNA
polymerase unwinds/untwist 10-20 nucleotides at a time nucleotides
added to 3 end as mRNA is built, the molecule peels away from DNA
and the double helix reforms Termination in prokaryotes there is a
terminator sequence (stop signal) eukaryotes transcribe a specific
sequence to stop transcription (creates pre-mRNA)
Slide 24
RNA Modifications (eukaryotes only) RNA processing: enzymes in
the nucleus modify pre-mRNA To help protect from degradation 5 cap
(modified G sequence) 3 (poly-A tail) RNA splicing: removal of
large portions of the RNA molecule (cut and paste) eukaryotes have
long stretches of non-coding DNA interspersed with coding segments
introns: non-coding segments exons: coding segments eventually
expressed
Slide 25
RNA Splicing introns are removed and exons are joined together
snRNPs: join together to form a spliceosome Once finished,
completed mRNA leaves nucleus to begin translation
Slide 26
Translation synthesis of a polypeptide using mRNA as
instructions occurs on ribosomes (rRNA) in cytoplasm tRNA:
transfers amino acids to growing protein each associated with a
particular amino acid anticodon: complementary RNA sequence to
mRNA
Slide 27
instructions for producing a protein uses three letters on mRNA
(triplet code) codon: mRNA triplet (3 nucleotides) methionine is
start stop codons UAA, UAG, UGA
Slide 28
3 stages Initiation mRNA, tRNA, and ribosome start with amino
acid methionine (initiator tRNA) translation initiation complex
Elongation amino acid added to chain via sites on ribosome (A-P-E)
elongation factors help process; reads 5-3 requires energy
Termination stop codons end synthesis, codes for release factor
release factors bind and protein is released via hydrolysis Protein
is then folded into appropriate shape with help of chaperonin
proteins http://www.dnalc.org/resources/3d/16-
translation-advanced.html
Slide 29
Oops! Mutation: change to genetic information Ultimate source
of new genes May be spontaneous or result from mutagens Point
mutations: change in single nucleotide (substitution) silent:
change doesnt alter amino acid sequence missense: changes one amino
acid into another (minor changes) nonsense: change codon for amino
acid into a stop codon (premature end to translation) Frameshift
mutation: add/lose nucleotides resulting in change to reading frame
of codons (not multiples of 3) Insertion or Deletion
http://www.bozemanscience.com/mutations/