Download GENETIC CONTROL MECHANISMS AND …

GENETIC CONTROL MECHANISMS AND MUTATIONS
Control Mechanisms




Over ______________ genes exist that code for proteins in humans
Not all proteins are needed all the time in cells i.e. Insulin is only required when glucose
levels are ____________ in the blood
Genes that are constantly expressed are called ______________________________
Gene regulation is vital to an organism’s survival
Gene Regulation





Genes are controlled at 4 levels in cells:
________________________– regulates which genes are transcribed
_________________________– mRNA undergoes changes in the nucleus
______________________– controls how often and how rapidly mRNA transcripts will be
translated into proteins
__________________________– control the rate at which a protein becomes active
Regulation using Operons




An operon is a ____________________________ consisting of :
____________________, a_________________ , separated by a short sequence of bases
known as an ___________________
Only _________________ use operons to regulate genes and their respective products
Two examples of operons are the ______ operon and the ______ operon
The lac operon


E. coli bacteria breaks down lactose using ___________________ enzyme ( 3 structural
genes – lac Z, lac Y, and lac A)
Aka: lactase
Lac operon : off

When lactose is absent a ________________ protein (Lac1 protein) binds to the ______________ site which blocks the RNA polymerase from binding to the
________________ thus, no galactosidase is produced
Lac operon: on


The presence of lactose acts as an ___________ which binds to the Lac1 protein (repressor)
so it can no longer bind to the operator of the lac operon DNA
_____________________ can now bind to the _____________ region and transcribe the
galactosidase enzyme
The trp operon: off



This regulates genes for ______________ (an amino acid) production in prokaryotes
The Trp-operon is repressed when _________ levels of tryptophan are present
Tryptophan is a __________________ because it binds with the trp repressor protein and
________________ it
The trp operon: on


When levels of tryptophan drop, the repressor loses its shape and _____________ the
operator
RNA polymerase is free to bind to the ______________and _____________the trp operon
genes
Comparing lac & trp operons






Lac operon is an example of enzyme _______________
Trp operon is an example of enzyme _______________
Lac operon regulates breakdown lactose by regulating the production of ____________
Trp operon regulates production of _______________
High levels of lactose _____________ the lac operon
High levels of tryptophan _____________the trp operon
Mutations



Mutations are errors made in the ________ sequence that are _____________
Each of us have many _______________ mutations (most masked by an extra copy of each
gene)
If humans were _______________ , much of the world’s population would die due to these
mutations
Types of Mutations



There are 2 categories of mutations:
___________________ – mutations specific to one base pair
__________________________ – mutations involving large segments of chromosomes
Point Mutations








Silent mutations: result in no change in the ________________________ and therefore do
not cause any phenotypic change (recall the redundancy in the genetic code eg. UUU & UUC
code for phe)
__________________ : arises when a change in the base sequence of DNA alters a codon,
leading to a ______________ amino acid being placed in the protein sequence.
Nonsense mutation: converts a codon specifying an amino acid to a _______ codon.
Nonsense mutations are often lethal to the cell as proteins produced are ____________
________________ : replacement of one base pair with another (missense and nonsense
mutations)
Deletion: elimination of a _____________
______________ : addition of a base pair
Frameshift mutation: deletion and insertion of one or two bases can cause a change in the
___________________ of a gene
A change in three bases will only affect _______ amino acid in the protein (less serious)
Chromosomal Mutations


___________________________________ are affected
These generally occur during ________________________





___________________ : relocation of groups of base pairs from one part of the genome to
another (some types of leukemia are associated with translocations)
Other mutations include______________ , ________________, _____________, and
_________________
Cells may contain extra or missing chromosomes due to __________________
A _________________ means one less chromosome (ie. Turner’s syndrome)
A ______________ means an extra chromsome (ie. Down’s syndrome)
Causes of Mutations



__________________________: caused by error in DNA replication
_______________________: caused by a mutagenic agent like UV radiation, cosmic rays, X
rays and certain chemicals (ie pesticides like DDT)
_____________ and ____________________are all the result of genetic mutations
Review
1. What are “housekeeping genes”?
2. Give three components of operons
3. How does the presence of lactose affect the lac operon of E. coli?
4. What affect does tryptophan have on the trp operon?
5. Why is a frameshift mutation more harmful than a missense mutation?
6. What kind of mutations involves large segments of DNA being altered?
7. Give some mutagenic agents