gene expression
DESCRIPTION
Gene Expression. 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. Operons. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Gene Expression](https://reader035.vdocument.in/reader035/viewer/2022062305/568166b2550346895ddab364/html5/thumbnails/1.jpg)
Gene Expression
![Page 2: Gene Expression](https://reader035.vdocument.in/reader035/viewer/2022062305/568166b2550346895ddab364/html5/thumbnails/2.jpg)
Cell DifferentiationCell 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
![Page 3: Gene Expression](https://reader035.vdocument.in/reader035/viewer/2022062305/568166b2550346895ddab364/html5/thumbnails/3.jpg)
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
![Page 4: Gene Expression](https://reader035.vdocument.in/reader035/viewer/2022062305/568166b2550346895ddab364/html5/thumbnails/4.jpg)
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
![Page 5: Gene Expression](https://reader035.vdocument.in/reader035/viewer/2022062305/568166b2550346895ddab364/html5/thumbnails/5.jpg)
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)
![Page 6: Gene Expression](https://reader035.vdocument.in/reader035/viewer/2022062305/568166b2550346895ddab364/html5/thumbnails/6.jpg)
Chromatin Complex of DNA and proteins DNA Packing
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)
![Page 7: Gene Expression](https://reader035.vdocument.in/reader035/viewer/2022062305/568166b2550346895ddab364/html5/thumbnails/7.jpg)
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.
![Page 8: Gene Expression](https://reader035.vdocument.in/reader035/viewer/2022062305/568166b2550346895ddab364/html5/thumbnails/8.jpg)
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.
![Page 9: Gene Expression](https://reader035.vdocument.in/reader035/viewer/2022062305/568166b2550346895ddab364/html5/thumbnails/9.jpg)
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
![Page 10: Gene Expression](https://reader035.vdocument.in/reader035/viewer/2022062305/568166b2550346895ddab364/html5/thumbnails/10.jpg)
RNA and Protein Processing
Alternative RNA splicing Different mRNA molecules
formed from the same primary transcript
mRNA degradation Protein processing Protein degradation
proteasomes
![Page 11: Gene Expression](https://reader035.vdocument.in/reader035/viewer/2022062305/568166b2550346895ddab364/html5/thumbnails/11.jpg)
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
![Page 12: Gene Expression](https://reader035.vdocument.in/reader035/viewer/2022062305/568166b2550346895ddab364/html5/thumbnails/12.jpg)
(b) Induction by nearby cells(a) Cytoplasmic determinants in the egg
Two differentcytoplasmicdeterminants
Unfertilized egg cell
Sperm
Fertilization
Zygote
Mitoticcell division
Two-celledembryo
Signalmolecule(inducer)
Signaltransductionpathway
Early embryo(32 cells)
Nucleus
NUCLEUS
Signalreceptor
![Page 13: Gene Expression](https://reader035.vdocument.in/reader035/viewer/2022062305/568166b2550346895ddab364/html5/thumbnails/13.jpg)
Body Plan Setup
Pattern Formation cytoplasmic
determinants inductive signals determine spatial
organization of tissues
![Page 14: Gene Expression](https://reader035.vdocument.in/reader035/viewer/2022062305/568166b2550346895ddab364/html5/thumbnails/14.jpg)
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)
![Page 15: Gene Expression](https://reader035.vdocument.in/reader035/viewer/2022062305/568166b2550346895ddab364/html5/thumbnails/15.jpg)
ras and p53 ras
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