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How is it that all cells in an organism have the same DNA, yet they are so different in function?
- Cellular Differentiation: process through which cells become specialized in structure and function
- -regulation of gene expression cause cellular differentiation
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What is ‘housekeeping’ gene expression like?
Housekeeping genes: required for basic cell maintenance so transcribes in all cells (ex. RNA pol)
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What do homeotic genes control?
- Homeotic genes
- are master control genes:
- -regulate
- groups of genes to determine body plan development
- -small
- mutations in homeotic genes have large effects on body plans
- -homeotic
- genes are conserved (similar) in widely different species
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What is an operon?
- -A cluster of
- genes with related functions
- -the control
- sequence that turns genes on or off
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How is the lac operon externally regulated? (know RNA polymerase, the promoter sequence, operator sequence, and the repressor protein, and what they do)
- -RNA
- Polymerase: makes RNA from DNA template by binding to the promoter sequence
- -Promoter
- Sequence: DNA segment upstream from the lac genes where RNA Pol binds to
- initiate transcriptions. Does not code
- for protein
- -Operator
- Sequence: A DNA segment that sits between the promoter sequence and the genes
- for lactose enzymes; can bind with repressor
- -Repressor: a
- molecule which can either bind to lactose or to the operator to physically
- block the attachments of RNA pol to the promoter sequence
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How is gene expression in a prokaryote different from expression in a eukaryote?
Eukaryotes
- -usually have
- two copies of each gene
- -gene
- expression is turned off without help from a regulatory protein
- -have separate
- regulatory sequence for each gene, although many share particular sequences or
- proteins involved in their transcription
-do not typically have operons
Bacteria
- -have no
- nucleus, so translation occurs immediately as mRNA is produced (no splicing)
- -genes are on
- unless a regulatory protein is blocking gene expression
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What is the mechanism of gene expression
in a eukaryote?
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How do microRNAs regulate gene expression?
microRNAs bind with mRNA to block translation and to target the mRNA for destruction
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What is RNAi?
RNA interference -biological process in which RNA molecules inhibit gene expression, typically by causing destruction to specific mRNA molecules
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What is special about stem cells?
Are produced through therapeutic cloning and are not completely differentiated
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Briefly explain the ways (shown below) in which protein presence is controlled in a cell: DNA packing Transcription factors and enhancers (regulation of expression- know about activators and repressors) mRNA processing and degradation microRNA Initiation of translation Protein activation and life span
- -DNA Packing:
- tightly packed DNA physically prevents RNA pol from transcribing the DNA
- -Transcription
- factors: protein involved in regulating DNA transcription in eukaryotes
-2 types
- -activators: proteins which bind to ENHANCER SEQUENCE or the
- promoter to encourage transcription
- -repressors: proteins which bind to SILENCER SEQUENCE or the
- promoter to discourage transcription
- -mRNA processing
- and decay: in many species one gene can make more than one protein
- -alternative splicing: a
- single mRNA transcript can produce more than one protein through different
- splicing
- -RNA decay: mRNA can last from
- hours to months; protein production is possible while mRNA is present
- -microRNA:
- small RNA molecules, bind with mRNA to block translation and target the mRNA
- for destruction ) commonly used in human cells)
- Initiation of
- translation: proteins can bind to mRNA on the 5’ end to block translation
- -Protein
- activation and breakdown: enzymes often must cut a polypeptide chain to make it
- a functional protein
- -proteins may last hours to
- weeks
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How does a signal transduction pathway communicate information about the environment to the nucleus of a cell?
- Occurs through
- a signal transduction pathway
- -a molecule outside the cell
- binds with a receptor protein
- -other molecules carry the
- information inside the cell
- -eventually, a transcription
- factor is activated
- -the transcription factor
- binds to DNA & regulates appropriate genes
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What does a microarray measure?
Measures mRNA expressed in a particular circumstance or condition
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What is a microarray ‘probe’?
each DNA spot contains picomoles of a specific DNA sequence
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What is a microarray ‘target’?
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What are: DNA, mRNA, cDNA?
DNA: Deoxyribonucleic acid is a molecule that encodes the genetic instructions mRNA: messenger RNA- carries information from DNA in the nucleus to cytosol in order to make protein cDNA:
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Why is reproductive cloning difficult in a laboratory?
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What is special about stem cells?
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Place embryonic stem cell, adult stem cells, and adult skin cells in order from least differentiated to most differentiated.
- Embryonic stem
- cells: extracted before differentiation has taken place, so may potentially be
- used to make new body tissues/organs and can divide indefinitely
- Umbilical stem
- cell: retrieved from cord at birth
- Adult stem
- cells: partially differentiated cells that replace a particular group of cells
- in differentiated individuals
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What is the difference between an
oncogene and a proto-oncogene?
- Oncogenes:
- genes that are currently causing cancer
- Proto-oncogenes:
- normal genes with the potential to cause cancer if mutated (through cellular
- mistakes or viral insertion)
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Potential exam question: Contrast the ways that a cell might regulate genes whose proteins perform a life-saving function due to a rapidly appearing threat vs genes whose proteins are helpful but not critical and only occasionally required. Mention the disadvantage and the advantage of regulating each type of gene in this way
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