1. Gene Expression

2. Cell Differentiation
Cell types are different because genes are expressed differently in them.
Causes:
Changes in chromatin structure
Initiation of transcription
RNA processing
mRNA degradation
Translation
Protein processing and degradation

3. Operons
Unit of genetic function consisting of related clusters of genes with related functions
A “switch” that controls enzyme production
Coded for by one transcription unit

4. Repressible Operons (The trp Operon)
Repressible Operon: always operates unless a repressor turns it off.
promoter: RNA polymerase binding site; begins transcription
operator: controls access of RNA polymerase to genes
transcription stops here when repressor is in place
repressor: protein that binds to operator and prevents attachment of RNA polymerase
Sometimes, a corepressor must be in place for the repressor to be active
Tryptophan (a.a.) synthesis
Transcription is repressed when tryptophan binds to the repressor, which connects to the operator

5. Inducible Operons (The lac operon)
Inducible Operon: Always off unless an inducer is present
Inducer attaches to the repressor and causes it to move so that transcription can occur
Lactose metabolism (lac operon)
lactose not present: repressor active, operon off; no transcription for lactose enzymes
lactose present: repressor inactive, operon on
inducer molecule inactivates protein repressor (allolactose)

6. Chromatin Complex of DNA and proteins DNA Packing Nucleosome
histone protein (+ charged amino acids ~ phosphates of DNA are - charged)
Nucleosome
”beads on a string”
basic unit of DNA packing
Heterochromatin
highly condensed interphase DNA (can not be transcribed)
Euchromatin
“true chromatin”
less compacted interphase DNA (can be transcribed)

7. Histone Modification
Genes within highly packed heterochromatin are usually not expressed
Chemical modifications to histones and DNA of chromatin influence both chromatin structure and gene expression
Acetylation prevents histones from packing tightly, which allows genes to be expressed.
Methylation causes histones to pack tightly so that genes are not expressed.

8. Epigenetic Inheritance
Expression of traits is not necessarily related to the nucleotide sequence
Some individuals may express traits from their genes where others will not based on histone modifications
One twin may express a trait or get a disease that the other does not, despite same genes
Schizophrenia
Some cancers
Etc.

9. Regulation of Transcription
Control Elements- noncoding DNA that regulate binding proteins
Enhancers- segments that influence how a gene is expressed
Often placed far from the actual gene

10. RNA and Protein Processing
Alternative RNA splicing
Different mRNA molecules formed from the same primary transcript
mRNA degradation
Protein processing
Protein degradation
proteasomes

11. Cell Differentiation
How cells become specialized in structure and function.
Determinants exist in the egg cell
Influence the expression of characteristics in different regions of cells
Once cells divide by mitosis, specific regions of the embryo will express genes differently

12. (b) Induction by nearby cells
Unfertilized egg cell
Sperm
Nucleus
Fertilization
Two different
cytoplasmic
determinants
NUCLEUS
Early embryo
(32 cells)
Zygote
Signal
transduction
pathway
Mitotic
cell division
Signal
receptor
Two-celled
embryo
Signal
molecule
(inducer)
(a) Cytoplasmic determinants in the egg
(b) Induction by nearby cells

13. Body Plan Setup Pattern Formation cytoplasmic determinants
inductive signals
determine spatial organization of tissues

14. Biology of Cancer Oncogene- cancer-causing genes
Proto-oncogene- normal cellular genes
How does a proto-oncogene become an oncogene?
movement of DNA; chromosome fragments that have rejoined incorrectly
amplification; increases the number of copies of proto-oncogenes
point mutation; protein product more active or more resistant to degradation
Tumor-suppressor genes
changes in genes that prevent uncontrolled cell growth (cancer growth stimulated by the absence of suppression)

15. ras and p53 ras p53 Produces Ras proteins
Hyperactive Ras protein causes cell cycle to continue (increased cell division)
Mutations involved in 30% of all cancers
p53
Tumor-suppressor gene
Activated by DNA damage
Turns on DNA repair or activates “suicide” genes
Mutations involved in 50% of all cancers