1. Ch 11- Controlling Gene Expression
Activator
Adult stem cells
Alternative RNA splicing
Carcinogens
Clones
Differentiation
Embryonic stem cells
Enhancers
Gene expression
Histones
Homeoboxes
Homeotic gene
Nuclear transplantation
Nucleosome
Oncogene
Operator
Operon
Promoter
Proto-oncogene
Regeneration
Regulatory gene
Repressor
Reproductive cloning
Signal-transduction pathway
Silencers
Therapeutic cloning
Transcription factors
Tumor-suppressor gene
X chromosome inactivation

2. What is gene expression?
Process by which genetic information flows from genes to proteins (genotype to phenotype)
Interaction of proteins and DNA turn prokaryotic genes “on” and “off”
Genes that are turned “on”- are being transcribed into RNA and translated into proteins (being expressed)
Turning a gene “on” or “off” controls the expression of certain genes (expressed as proteins) in a cell

3. Example:
E. coli – bacteria – regulates gene expression by environmental changes
lac operon- when lactose is present= cell needs to produce protein to break it down and use it
When lactose is absent= doesn’t want to bother making the protein to break down lactose
Promoter- site where RNA pol attaches
Operator- site that determines whether promoter can bind or not to RNA pol
Promoter + operator + genes to be transcribed = operon
Repressor- protein that binds to operator; blocks transcription
Regulatory gene- outside of operon; codes for repressor; always expressed
Repressor will only bind if certain molecules are present (fits into repressor)
Activators- proteins that turn operon “on” by binding to DNA
Makes RNA pol bind more easily

5. Essential aa so needs to make it when not available

6. Cell differentiation produces variety
Differentiation- cells become specialized in structure and function
Results from selective gene expression
Doesn’t cause change in DNA
Ex: muscle contraction protein gene: turned on in muscle cells, off in RBC’s
Differentiated cells maintain genetic potential
Plant cells can dedifferentiate and give rise to a new plant
Regeneration- body part can be re-grown

7. Carrot cloning

8. Clones and cloning Clone- genetically identical organism
Nuclear transplantation- nucleus of an egg is replaced with body cell nucleus
Cloning in the news:
Reproductive
Helps in research, agriculture, medicine
Therapeutic
Embryonic stem cells- can give rise to any specialized body cells; immortal in a culture
Can study the effects of changing genes, clone farm animals with desirable traits, clone animals that produce valuable drugs (Ex sheep that secrete human blood protein in their milk)
Therapeutic- produce human organs in animals

10. Controlling gene expression in eukaryotes
How DNA is packaged
Histones- small proteins; helps coil DNA
Nucleosome- “bead” consisting of 8 histones and DNA wound around it
String of “beads” is then coiled, which is then coiled on itself
Packaging prevents RNA pol from reaching DNA
Histones must loosen grip on certain part of DNA, then RNA pol may bind to DNA

13. Example of how DNA packaging effects gene expression:
X-inactivation
In female mammals, 1 X chromosome is so tightly compacted that it is inactive, even during interphase
Initiated early in embryonic development
A random event
Heterozygous females on X chromosome will express different X-linked alleles
Ex: tortoiseshell cat

15. Complex proteins control eukaryotic transcription
More regulatory proteins and control sequences in eukaryotes
Each gene has its own promoter and control sequence
Activators are more important than repressors usually (default is “off”)
Except for activities that must happen continuously, Ex: glycolysis, their default is “on”

16. Complex proteins control eukaryotic transcription
Transcription factors- regulatory proteins that turn on eukaryotic transcription (in addition to RNA pol)
Activators are one type that bind to enhancer DNA sequences; sequences that regulate far from gene
DNA bends and TF’s bind to create an area where RNA pol can bind to
Silencers- are sequences that repressors bind to; stop transcription initiation
Coordinating gene expression- eukaryotes rarely have operons, so enhancer sequences and transcription factors are important for the transcription of genes

17. Expression is also regulated by alternative RNA splicing
RNA can be spliced differently to yield different polypeptides from the same gene
Ex: sex of fruit flies
Can also affect when mRNA molecules move into cytoplasm

18. Translation and even proteins can also be regulated
mRNA breakdown- Determines how many proteins are made
In prokaryotes- mRNA breaks down quickly
In eukaryotes can last much longer
Initiation of translation- proteins are in place to control the start of translation; sometimes determined by available chemicals
Protein activation- polypeptides are cleaved to yield smaller active protein
Protein breakdown- selective breakdown; response to change in environment

19. Genetic Control of Embryonic Development
Gene expression can determine body plan
Concentration gradients of mRNA and proteins determine body layout
Homeotic gene- master control gene; regulates genes that determine body plan
Many proteins act as signals to notify bordering cells

20. Within homeotic genes there are sequences that are very similar between all eukaryotes
Homeoboxes- nucleotide sequences that code for part of a protein that can bind to the DNA of the gene that it regulates

21. Signal transduction
Series of molecular changes that converts a signal on the cell surface to a response within the cell
Cell to cell signaling
Uses relay of proteins to initiate transcription

22. Genetics behind cancers
Oncogene- gene that causes cancer
Proto-oncogene- normal gene that has the potential to become an oncogene
Many code for growth factors (stimulate cell division)
Can become oncogenes a few ways
Mutation, having multiple copies of gene, movement of gene to new location with new controls

23. Tumor-suppressor genes- produces proteins that prevent uncontrolled cell division
If there is a mutation a cell might start to divide excessively
Figure 11.15B in chapter

24. Oncogene proteins and faulty tumor-suppressor proteins can affect signal transduction pathways
Oncogene protein can be hyper active and stimulate cell division
Tumor-suppressor protein can stop protein that inhibits cell division from being produced

25. Cancer does not usually start from 1 mutation in a somatic cell
Oncogene can be activated then tumor-suppressor genes can be inactivated (usually more than 1 is), this possibly produces a tumor
An accumulation of mutations in a lineage of somatic cells can cause a malignant cell
Avoiding carcinogens can reduce risk
Carcinogen- factors that alter DNA and make cancerous cells
Ex: X-rays, UV light, tobacco (chemicals),
When something can cause a mutation in DNA it runs a risk of affecting the cell division control system