LECTURE 10: Stem Cells and Control of Gene Expression

Question 1

State the difference between housekeeping genes and genes that are differentially expressed

Answer 1

‘housekeeping genes’- Genes encoding basic cell function
proteins (e.g. ATP synthase, tubulin) are on in all cell types.

Only a fraction of all the genes may be expressed in any one cell type (spatial expression), or at any given point in time (temporal expression)
Different genes are either on or
off. Those that are ‘on’ can be tuned for varying levels of transcriptional output

Question 2

Different cells__________________

Answer 2

express different sets of genes- gives rise to different cells in the body
*not all cells express the same genes even though they have the same genome
EXCEPTIONS- red blood cells

Question 3

spatial expression

Answer 3

different cells expressing different genes

Question 4

temporal expression

Answer 4

same gene expressed in 2 different cells but at 2 different points of time

Question 5

give examples of temporal and spatial expression

Answer 5

2. Some genes are only expressed when stem cells differentiate after division and are then turned off (temporal)
3. Some genes are only expressed in cell types with specialized functions (spatial); producing glc in liver cell will only produce gene for that
4. Some genes are only expressed in response to certain stimuli (e.g. hormone induction, environmental changes)
   - exposed to low levels of O2

Question 6

Explain why the genome from a epithelial cell can be used to create an entire organism, or why an isolated plant cell
can grow into an entire plant

Answer 6

Because of the same genome being in each cell of an organism, each cell type has the potential to become any other cell type.

However, they usually don’t because developmental programming has each cell type mostly ‘fixed’ as one type or subset
Because the genome has the instructions for all cell types, we can isolate individual cells and make those cells grow into functional multicellular organisms. But each cell type only expresses it’s subset of genes!

*CELLS by embryogenesis all start the same and slowly differentiate

Question 7

What is the main difference between different cell types?

Answer 7

the main difference between different cell types is differential gene expression

Question 8

List the five main levels of regulation that dictate whether a protein will be active inside of a cell
a. Describe examples of processes that occur at each level

Answer 8

1. Epigenetic level
   - changes in gene transcription translation thats not dependent on actual gene sequence
   E.g. heterochromatin or euchromatin, nuclear position effects, DNA methylation
2. Transcription level
   e. g. Regulation by transcription factors, interplays with epigenetic level control
3. mRNA Processing level
   different messenger RNAs made from a given gene (alternative splicing)
4. Translational level
   -mRNA but not proteins
   i.e. how much of the mRNA is made into protein
   Control of mRNA lifetime (e.g. polyA tail ‘timer’, elements in 3’ UTR), miRNAs, etc.
5. Post-translation
   Protein lifetime (e.g. ubiquitination), post translational modifications (phosphorylation, etc.)
   - mRNA but 2 proteins or more

Question 9

Describe what a transcription factor is and how they operate (structure/function)

Question 10

promoter.

Answer 10

regulatory DNA sequences that are‘upstream’(or5’)of the protein- coding portion of a gene. Together, these sequences are called