Download Chapter 16 Research Discovery of DNA`s Structure and Function

Chapter 16 Research
Discovery of DNA’s Structure and Function
1868- Johann Friedrich Miescher​ discovered nucleic acids
1928- Fred Griffith​ found that proteins or nucleic acids could be the hereditary material.
1944- Oswald Avery ​found that DNA is a transformative substance (mouse experiment)
1951- Linus Pauling ​discovered the helical structure of proteins
1952​- ​Hershey & Chase​ proved DNA was the hereditary material.
1953- Watson & Crick​ discovered the structure of DNA
DNA Structure
● Made up of deoxyribose, a phosphate group, and one of 4 bases. (A,G,C,T)
● Edwin Chargaff found that the bases differ in amounts from species to species, and that
the amount of A=T, and the amount of G=C
● Rosalind Franklin discovered that DNA is long and thin, that it is helical, and that the
structure is repetitive.
● Bases are bonded together via hydrogen bonds
● Backbone is made of sugar-phosphate linkage chains
● Base pairing is constant for all species
Replication
1. The two strands are unwinded by helicase, beginning at the replication fork
2. Binding proteins bind to the strands to prevent re-winding.
3. RNA primase adds RNA primers to strands
4. DNA Polymerase III adds complementary bases to leading strand in 5’-3’ direction
5. Bases are added to lagging strand discontinuously in Okazaki fragments in the 3’-5’
direction
6. DNA Polymerase I removes RNA primers from lagging strand and adds complementary
bases
7. DNA Ligase joins the gaps between Okazaki fragments
8. DNA Polymerase I & III proofread the strands and repair any mistakes
a. Error rate following the proofreading repair is low, but not zero. These mutations
provide the genetic variation that fuels natural selection
​Repair
● DNA Polymerases can correct incorrect base pairing
● If damaged by exposure to harmful substances/environments, a nuclease cuts out and
replaces parts of DNA
Chromosome Structure
These molecules are made through a complex system of packing, and are different in
eukaryotes and bacteria. Bacterial chromosomes are double stranded and circular with little
protein, while eukaryotic chromosomes are linear with a large amount of protein.
Lab References
● Protein Synthesis Review Activity, Restriction Enzyme Lab, DNA Scissors, DNA Goes to
the Races, Connect the Dots Lab
DNA Replication Poster
In class we made a poster detailing the process of DNA replication, how it works, and what is
needed for it to happen.
Chapter 17 Research
-RNA has ribose sugar and uses the base uracil instead of thymine
Types of RNA
Messenger - Carries the blueprint for protein assembly
Transfer - Carries the correct amino acid to the ribosome and pairs with the mRNA codon for
that amino acids
Ribosomal - Combines with proteins to make ribosomes
Central Dogma: DNA → RNA → Protein
Transcription ≠ Replication
-Only one region of the DNA strand serves as a template
-RNA polymerase is used instead of DNA polymerase
-RNA is single stranded
Transcription : DNA → RNA
1.One of the DNA strands serves as a template strand
2.RNA polymerase bind to a promoter region and moves along the template strand, ordering
complementary nucleotides making the RNA transcript
mRNA Modifications : New mRNA must be modified before it can be used
1.5’ end is capped with a nucleotide that serves as a start signal for translation
2.3’ end has a “Poly-a” tail, made of about 100 molecules of adenylic acid, attached to it
3.Noncoding introns are snipped out and the coding exons are spliced together by
spliceosomes
The mRNA in now a useable molecule
Codons
-Codons: Triplets of mRNA bases
-Read in the 5’ to 3’ direction
-Codons specify for one of 20 amino acids
-Different codons can code for the same amino acid
Translation of mRNA
Initiation​ - A complex forms made of initiator tRNA, a small ribosomal subunit, mRNA, and a
large ribosomal subunit
Elongation​ - A start codon in the mRNA starts translation, tRNAs deliver amino acids based on
the codon-anticodon pairings, and peptide bonds join the amino acids into a polypeptide chain.
Termination - ​A stop codon is read and the polypeptide chain is released
Chapter 18 Research
The genome of an organism contains many genes, but not all of those genes are expressed in
cells.
Prokaryotic Gene Expression
❖ Bacterial cells are able to modify the activity of enzymes. They can also control the
production levels of enzymes and regulate gene expression.
❖ Promoter - specific nucleotide sequence in the DNA of a gene that binds to RNA
polymerase, positioning it to start transcribing RNA at the correct place.
❖ Operator - nucleotide sequence close to the start of an operon where the active
repressor attaches.
❖ Operon
➢ found in bacteria and phages; made of a promoter, operator, and genes whose
products function in a common pathway
➢ Operator - segment of DNA that operates as the switch
➢ Promoter - RNA polymerase can bind with the DNA to begin transcription
➢ Genes - nucleotide sequences that encode subunits of the enzyme
Repressor Protein​ - binds to the operator and blocks the attachment of RNA polymerase to the
promoter, preventing transcription of genes
Regulatory Genes​ - codes for a protein that controls the transcription of another gene or group
of genes
Repressible operons​ are on by default, but can be repressed when a molecule binds to the
regulatory protein. The ​trp operon is an example of a repressible operon.
Inducible operons​ are off by default, but can be induced when a molecule interacts with a
regulatory protein. The ​lac operon is an example of an inducible operon.
Differential Gene Expression​ is the expression of different groups of genes by cells with the
same genome. Gene expression can be controlled by chromatin modifications.
Epigenetic Inheritance​ occurs when the inheritance of an allele from the male or female parent
affects the expression of the allele in the offspring.
Alternative RNA Splicing​ can result in multiple proteins being coded for from the same RNA
transcript. Different segments of the RNA transcript can be treated as introns or exons, allowing
for different proteins to be derived.
Post-transcriptional Control​ includes the regulation of the amount of mRNA in the cytoplasm.
The longer the mRNA, the more proteins that can be formed.
Oncogenes​ are found in cellular or viral genomes. They trigger molecular events that can
promote cancer.
Proto-oncogenes​ are normal genes that have potential to become oncogenes.
Big Idea Connections
❖ The process of evolution drives the diversity and unity of life. M
​ utations in the DNA
during replication or caused by environmental factors can sometimes be beneficial to a
species, increasing diversity.
❖ Biological systems utilize free energy and molecular building blocks to grow, to
reproduce and to maintain dynamic homeostasis. ​Gene expression and DNA
replication require specific regulation and cooperation between systems to maintain
homeostasis.
❖ Living systems store, retrieve, transmit and respond to information essential to
life processes. ​DNA replication allows for hereditary information to be passed down and
continue life.
❖ Biological systems interact, and these systems and their interactions possess
complex properties. ​Transcription and translation are both complex processes that
come together to form the complex process of DNA replication.