BIOSC 0160: EXAM 1
68 Cards in this Set
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pleitropy
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1 gene for many Traits
--ex. Down's Syndrome, Sickle Cell
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sickle cell heterozygotes
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--have some traits of the disease but don't suffer the symptoms
--cannot be infected by malaria b/c of half sickle cells half normal cells
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quantitative traits
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traits which vary by degrees
--also known as continuous traits
--influenced by interactions of genes w/other genes and interaction w/environment
EX. skin colors-many diff combos
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Sex-linked genes
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Any gene that is located on the sex chromosome
--Most sex-linked genes are on the x chromosome
Most are recessive and appear more often in males because males only need one x chromosome to be affected
Examples: color blindness and hemophilia (x-linked rec)
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linkage
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physical association among genes on the same chromosome
---more difficult for linked genes to cross over
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The Hershey-Chase Experiment
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labeled protein and DNA with isotopes inside viruses to figure out what (genetic) material is exchanged between bacterium
DNA is exchanged
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DNA structure
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5'-->3'
nucleotides connected by phosphodiester bonds (connect phosphate group to hydroxyl group)
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purines
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A + G
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pyrimadines
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C + T(U)
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C+G how many H bonds?
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3 H Bonds
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A + T how many H bonds?
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2 H bonds
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size of the human genome
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3 x 10^9 base pairs
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time required for S phase of cell cycle
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(DNA synthesis)
takes approx. 10 hrs
--80,000 base pairs/second
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how many times is our genome doubled?
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43 times
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Helicase
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Untwist the double helix at replication fork, seperating parental strands, break H bonds
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primase
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lays down RNA primer. 1 on each strand (on both sides of replication fork)
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DNA Polymerase II
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starts by connecting to primer laid down by primase and continues to extend strand by adding base pairs
--proofreads for errors and corrects them
(COMES BEFORE DNA POLY I)
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leading strand
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continuous from 5' to 3' w/no breaks
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lagging strand
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also called Okazaki fragment
--discontinuous b/c RNA Primase must start it again multiple times
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Ligase
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connects Okazaki fragments
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DNA polymerase I
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removes primers and fills gaps with nucleotides of DNA
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Topoisomerase
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cuts the DNA downstream and release the tension in the DNA as it unwinds.
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Sliding clamp
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holds DNA polymerase in place
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Single-strand DNA binding proteins (ssbp)
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Stabilizes single stranded DNA on lagging strand
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DNA --transcribed-> mRNA
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--build mRNA 5' to 3' using comple. bases
--start transcribing at AUG
--read to end of needed sequence
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mRNA --translated-- Protein
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--Read mRNA from 5' to 3' in triplet codons beginning with AUG
--look up codons in amino acid chart
--end with stop codon
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challenges of transcription
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--accurately extract info from DNA
--work with a small piece of chromosome (determine which strand, where to start/stop)
--know when to express gene (responding to environment, cell specialization, etc)
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how do we find the gene to transcribe?
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Promotor DNA and sigma factor proteins attract the machinery needed to start
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the challenges of translation
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convert info from 1 format to another
--hold everything together in space and time so that recognition and bonding can occur
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aminoacyl tRNA
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a strand of RNA looped together multiple times and sometimes base pairs align and bond via hydrogen bonds (3D structure)
--bottom has an anticodon that matches up with codon on mRNA strand
--tRNA translates a codon into an amino acid
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Information flow of Prokaryotes (translation)
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a.) bacterial ribosomes during translation
b.) in bacteria, transcription and translation are tightly coupled
--ribosome translates mRNA as it is being synthesized by RNA polyribosome
*****Prokaryotes transcribe from 3' to 5' on coding strand but Ribosomes translate from 5' to 3' for p…
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information flow of eukaryotes (translation)
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*transcription and RNA processing in nucleus
**translation in cytosol
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Polyribosome
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- when a number of ribosomes can translate a single mRNA simultaneously
-enable a cell to make copies of a polypeptide very quickly
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initiation of transcription in prokaryotes
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Sigma factors---bind to -10 and -35 boxes on promotors in bacteria
--RNA polymerase II doesn't bind to promoter by itself. it's general purpose and specificity comes from other parts of the complex
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initiation of transcription in eukaryotes
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--basal transcription factors-bind around TATA box at -30
--RNA polymerase II doesn't bind to promoter by itself. it's general purpose and specificity comes from other parts of the complex
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RNA Processing (eukaryotes)
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a.) splicing--introns must be removed from RNA transcripts.
1. template DNA-->introns removed
2. Primary RNA transcript (splicosome) results in spliced transcript
b.) adding modified guanine to 5' cap and a Poly A tail to 3' end
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ribosomes (structure, so on)
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--small and large subunits
--E (exit), P (polypeptide), A (amino acid attached) sites
--breaking bonds w/ tRNA
--building bonds btwn amino acids
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RNA Processing in Prokaryotes
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does not occur in prokaryotes
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elongation of polypeptide
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1.) incoming aminoacyl tRNA
2.) peptide bond formation
3.) translocation (tRNA moves left, new tRNA moves into place)
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Translation Termination
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1.)Release factor is a PROTEIN, not a tRNA.
2.)then polypeptide is released
3.) ribosome subunits separate
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error checking in DNA synthesis
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a.) DNA polymerase III adds a mismatched base
b.) but it notices and corrects it.
**error rate of 1 in 10^7 bases
**this is an exonuclease (working at the end)b/c DNA backbone is not in place
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Error checking damaged DNA
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Nucleotide Excision Repair
---thymine dimer--cross bonding btwn bases, creates a kink in the DNA
---this is endonuclease-(working in the middle) b/c DNA backbone IS in place
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mutations vs. mistakes
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--mutations are changes in DNA sequence
--mistakes are problems with extraction of information
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silent mutation
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change in nucleotide that doesn't change the amino acid
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missense mutation
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change in nucleotide that doesn't change the amino acid
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nonsense mutation
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change in nucleotide that results in an early stop codon and effectively ends the polypeptide early
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frameshift mutation
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addition or deletion of a nucleotide
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Mutagens and Carcinogens
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*Physical
--ionizing radiation(X-rays), UV rays
*Chemical
--DNA reactive chemicals, base analogs
*Biological
--Viruses, bacteria, transposons
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Cancers mostly occur from...
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changes in regulatory proteins affecting things like cell cycle control
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Mitotic Mutations--Recombination
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--unequal crossing over could cause problems
--Nondisjunctions-chromosomes don't separate properly and result is anaploidy (wrong # of chromosomes n+1 or n-1)
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genes (structural and regulatory)
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structural--code for proteins that act in structure or metabolism
regulatory--code for RNA or proteins that regulate the expression of other genes-act by binding to DNA
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types of gene control
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*positive--stimulates transcription; regulatory protein called an activator
*negative--suppresses transcription; regulatory protein called a repressor
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operons are either
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*inducible-normally off but can be turned on (lac operon)
*repressible-normally on but can be turned off (trp operon)
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negative control of the lac operon
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a.) repressor present, lactose absent
--repressor binds to DNA and blocks transcription of lac z, etc.
b.) repressor present, lactose present
--lactose (inducer) binds to the repressor
--repressor releases from DNA and transcription occurs
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positive control of the lac operon
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*regulatory molecule (CAP) is an activator
*activator does not bind unless it has cAMP (ligand) attached
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relationship of glucose level to lac operon
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the amount of cAMP and the rate of transcription are inversely proportional to the concentration of glucose
*high glucose--no transcription
*low glucose-frequent transcription
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trp operon
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--is usually active
*if no trp is present, it will not be expressed
*normal levels of trp-will be transcribed
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DNA packaging
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double stranded helix
--wrapped around histones (groups of 8)
---condense into chromatin fibre
----condensed chromatin forms chromosome
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net charge and name of a group of 8 histones
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+, called a nucleosome
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what is the function of HDAC?
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strips histones of acetyl groups, which allows chromatin to condense
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what is the function of HAT?
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loosens chromatin and attached acetyl groups to histones
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structure of eukaryotic gene
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*promotor-each gene has its own. where RNA polymerase binds (w/additional proteins)
*introns and exons-not an operon
*proximal element-like CAP binding site---involved in positive control of gene. located before the promotor
*enhancers-far away, up or downstream
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basal transcription complex
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*only in eukaryotes
*regulatory regions of DNA
*produces regulatory proteins
*consists of: RNA Polymerase II, basal transcription proteins, promotor proximal elements
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alternative splicing
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on one gene, 2 proteins can be coded for by alternative splicing of exons
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alternative splicing
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miRNA acts as specificsignal for RISC protein(which breaks downmRNAs)
*hairpin is due to complementary base pairing
*specificity is by complementary base pairing
*a form of post-transcriptional control
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cancer biology
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2 common causes:
*mutations in tumor suppressor genes
*mutations in protooncogenes
Cancer is a suite of diseases w/common features like tumors, invasion of other tissues, etc.
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P53-tumor suppressor gene
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normally functions by repressing the cell cycle
--gene codes for a transcription factor
--mutation can make it ineffective
--carcinogens increase the rate of mutations
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RNA polymerase I
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transcribes genes to produce functional mRNA
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BIOSC 0160: EXAM 2 EVOLUTION AND SPECIFICATION