Gene regulation and mutation

the process of producing a protein encoded by a gene

gene expression (transcription + translation)

• if a protein is being made, the gene for the protein is “expressed”

depending on the needs of the cell + organism..

gene expression can be turned on/ off

regulation of gene expression can also explain how

we have different cell types despite almost all of our cells in our body having the same DNA + genes

difference in gene expression

• all cells in our body have the same genes, but dont all express the same ganes

• different cell types produce different proteins and have different functions

where/ when can gene expression be controlled

transcription, post transcription (mRNA), and post transcription (protein)

transcription factors

proteins that can either recruit or block RNA polymerase from transcribing a gene

• bind directly to special DNA sequences near promoters

activators

transcription factor that recruit RNA polymerase to genes, they “activate” gene expression

repressors

transcription factor that blocks RNA polymerase to genes, they “repress” gene expression

transcription factors are specific for

one gene or small subset of genes

-different cell types have different combinations of these transcription factors to turn genes on or off depending on function of cell

-ex. HFN1a is a transcription factor that turns on the lactase gene in intestinal cells

epigenetics is a way

transcription can be regulated

what does epigenetics include

• any factors that alter chromatin without changing DNA

• histones can be modified by adding chemical groups to their “tails” which are dangling amino acids (depending on their chemical groups histones can move closer together or further apart)

close histones

• genes in compact DNA cannot be expressed because transcription factors and RNA polymerase cant reach

spaced out histones

• genes in non-compacted DNA are accessible for transcription

gene expression can also be controlled by

alternative splicing

what is alternative splicing in terms of exons and introns

• when a gene is expressed, both exons and introns are initially transcribed into RNA during transcription

• ultimately the exons are “spliced” together to produce the true protein coding RNA

in the phenomenon of alternative splicing, some genes can

code for protiens

• different combinations of exons can be included or excluded to produce multiple types of proteins from one gene

how many protein coding genes do humans have and how many proteins

20,000

100,000

example of alternative splicing

protein called troponin is involved in helping muscles contract, each type of muscle cell in humans have a unique form of troponin due to alternative splicing

what are mutations

• changes to DNA/ gene sequences (can cause change in proteins they code for)

• can lead to cancer

2 types of mutations

1. point mutations

2. chromosomal aberrations

what are point mutations and what are the three types

single nucleotide changes

1. substitutions: when one nucleotide changes to another, alters codon sequence

2. insertions

3. deletions

• both add/subtract a nucleotide, causes a change in “frameshift” in which all codons after the mutation will be altered, results in being extremely mutated (non functional)

chromosomal aberrations

entire sections of a chromosome are altered, deleted, relocated, or duplicated

3 ways mutations can happen

1. spontaneous mutations: arrise by accident as DNA duplicates itself when cells are dividing

2. radiation-induced mutations: ionizing radiation has enough energy to disrupt atomic structure by removing tightly bound electrons

3. chemical-induced mutations: some chemicals can also react with the atoms in DNA molecules