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Chapters 13, 14, 15, and 17

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Juliet Morales

on 18 March 2014

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Transcript of Chapters 13, 14, 15, and 17

Gene Expression: From Gene to Protein
Gene Expression is a process by which a gene (DNA) is used to synthesize proteins.
- An example such as albinism is attributed to a faulty gene that codes the wrong information.
-In such cases, the gene could code the wrong protein, or even be absent.
Archibald Garrod proposed the idea that inherited diseases could be from the lack of a specific enzyme.
-Ex: Phenylketonuria
Neurospora experiment: Neurospora cells had a single gene disabled and noticed the mutant Neurospora were unable to grow on minimal medium while the non-mutants were able. Beadle and Tatum concluded that the mutants could not synthesize an important nutrient. This proved that "the function of a gene is to dictate the production of a specific enzyme."
Mutations
Mutations are changes to genes.
-Point mutations change a single nucleotide pair.
-Substitution mutations replaces a nucleotide and its corresponding nucleotide with another pair
-Insertions and deletions are the addition or removal of nucleotide pairs.
These changes to genes can cause a silent mutation, missense mutation, or nonsense mutation.
-A silent mutation has no effect on the outcome trait of the gene.
-A missense mutation will have little effect on the protein since only 1 amino acid changes.
-A nonsense mutation stops translation because when the pair was changed, it was changed into a stop codon
Important Contributors
In Bacteria:
In Eukaryotes:
Regulation of Chromatin
Chapters 13, 14, 15, and 17
Transcription
DNA contains the nucleotides: Adenine, Cytosine, Guanine, and Thymine
RNA is the same except that instead of Thymine, there is Uracil.

Transcription is the synthesis of RNA from an original strand of DNA.
- In DNA replication, a DNA strand is made from the original DNA (template) strand.
- Then, that DNA strand serves as a template strand to make RNA. This is done by the RNA polymerase.
- Assembles in 5' to 3' direction.
- RNA polymerase starts at the promotor and the DNA sequence transcribed into RNA is a transcription unit.
- The pre-mRNA is given a 5' cap and a Poly-A tail and is removed of all introns and left with the exons (RNA splicing). After, it is moved into the nucleus.
Translation
The resulting mRNA strand from transcription is used in the synthesis of a polypeptide in a process called translation.
- The mRNA nucleotide sequence leaves the nucleus and into the ribosomes, the sites of translation (in eukaryotes).
- In the ribosomes, the mRNA undergoes translation to produce the amino acids for the protein.
Codons are mRNA nucleotide triplets.
There are 20 different amino acids which are made from making triplets of nucleotides. There is a combination of 64 different triplets.
60 of these combinations make up the amino acids while 1 makes a start codon, signaling the start of a nucleotide sequence and the other 3 make stop codons that signals when that nucleotide sequence ends for the protein.
Amino acids are read from 5' to 3'.
tRNA is used to transfer amino acids to the polypeptide in the ribosome by pairing up its anticodon to the codon in the mRNA. tRNA is 3' to 5'
It starts at a start codon and ends at a stop codon.
The Molecular Basis of Inheritance
DNA is the genetic material
DNA is the molecule that carries the genome
long thought to be proteins
Made in double helix, with specific base pairs (A-T; G-C)
DNA replication takes many proteins
Helicase separates two parent strands
DNA pol III creates leading strand continously and the lagging strand in Okazaki fragments
Primase adds RNA primers
DNA pol I changes primers to DNA
DNA ligase connects DNA fragments
DNA Polymerase corrects any mismatched nucleotides
A Chromosome is DNA molecule tightly wound around proteins
DNA of bacteria supercoils into a dense nucleoid
DNA in eukaryotes condenses around many histones
Frederick Griffith
Derrick Chen, Francis McMahon, Juliet Morales, and Anthony Velte
Chapter 13
Chapter 14
Chapter 15

Regulation of Gene Expression
Chapter 17
VIRUSES
Discovery?
Experiments:
Adolf Mayer rubbed sap from Tobacco Mosaic Disease infected plants with sap from healthy plants. Believed small bacteria not visible under microscope
Second attempt at experiment by Dimitri Ivanowsky by using filter to catch bacteria. Disease still produced. Still believed bacteria were cause.
Martinus Baijerinck's experiments revealed that pathogen infected within host cell.
Wendall Stanley crystallized Tobacco Mosaic Virus. How? Are they cells?
Structure
Genome-
can be single- or double-stranded, RNA or DNA
Capsid-
protein shell enclosing genome,
may be rod-shaped, polyhedral, or more complex
subunits called capsomers
Envelopes
- membranes derived from previous host
phospholipids, glycoproteins, and proteins
help to infect host
Infecting
other cells!
"Obligate intracellular parasites"
Lacking equipment for protein synthesis!
Need a host cell to replicate
Limit on number of host species, called host range of the virus
Identify host cells with "lock and key" fit
Viral protein encoded reprograms the cell
Retroviruses
Phages
Virulent,
only replicates through lytic cycle
Temperate,
replicates through either cycle depending on conditions
Simplified Viruses
With DNA:
With RNA:
*viruses that use reverse transcriptase*
Fighting Viruses!
Some viruses can mutate regularly, like the flu virus!

Further research is being conducted.

Vaccines-
variant of the virus that causes the
immune system to create antibodies against pathogen

*HIV is a retrovirus!
Works Cited:
Biology in focus. (2014). Boston, MA: Pearson Education.
The lytic and lysogenic cycles of phage lamda, a temperate phage [Image]. (n.d.). Retrieved from http://thegeneticsofvirusesandbacteria.weebly.com/diagrams.html
The lytic cycle of phage T4, a virulent phage [Image]. (n.d.). Retrieved from http://thegeneticsofvirusesandbacteria.weebly.com/diagrams.html
[Phage]. (n.d.). Retrieved from https://dbscience4.wikispaces.com/Jillian
The reproductive cycle of an enveloped RNA virus [Image]. (n.d.). Retrieved from http://thegeneticsofvirusesandbacteria.weebly.com/diagrams.html
A simplified viral reproductive cycle [Image]. (n.d.). Retrieved from http://thegeneticsofvirusesandbacteria.weebly.com/diagrams.html
Viruses [Image]. (n.d.). Retrieved from http://www.bbc.co.uk/bitesize/ks3/science/organisms_behaviour_health/disease/revision/2/
Respond to environmental changes through
operons!
Inducible Operon/
Catabolic Pathways
Reg. protein is typically active, no transcription





An inducer, typically the substance the structural proteins break down, will inactivate it
RNA polymerase is no longer blocked
Repressible Operon/
Anabolic Pathways
Reg. protein is typically inactive, transcription occurs






An corepressor, typically the substance the structural proteins synthesizes, will activate it
RNA polymerase is now blocked
Structure & Function:
Promoter
and
regulatory

gene
"upstream"
promoter for synthesizing regulatory protein for gene
regulatory gene codes for reg. protein that controls operon
Operon
itself consists of:
promoter
for operon (including
operator
) and
structural genes

promoter for binding RNA polymerase for transcription of structural genes
operator will stop transcription if reg. gene is bound to it (site of inhibition)
structural genes code for various proteins/enzymes to perform certain metabolic processes
Two types....
Funny thing about the lac operon...
Positive gene regulation also plays a role.
Because lactose isn't the cells first choice as an energy source (glucose is),
in presence of lactose and glucose, some lac operon is synthesized
in presence of lactose and absence of glucose, lots of lac operon is synthesized
Histone Acetylation - promotes transcription by opening chromatin
DNA methylation - reduces transcription
- epigenetics (licking rat pups!)
Transcription
RNA Processing
miRNA / siRNA
mRNA Degradation:
if bases complimentary, mRNA is degraded
Translation:
if bases not complimentary, translation is blocked
Translation
regulation of transcription factors
Proteins
has life span before degradation
ALSO!
Genetic Recombination in Prokaryotes
Transformation
uptake of foreign DNA from surroundings

Transduction

Conjugation
through 3rd party temporarily joined
Hershey and Chase
Meselson and Stahl
Full transcript