Unit 3 Part 2 Flashcards
D2.2 Gene Expression
Gene expression
Mechanism by which genetic info in a gene is expressed as a functional protein
- Functional protein like an enzyme will effect the organism’s phenotype
What does gene expressions involve?
- Transcription of a gene to produce mRNA
- Translation of mRNA by ribosomes to produce a functional protein
Phenotype
Observable traits that are a result of an organism’s genotype and environmental factors
Genotype
The combination of alleles inherited by an organism
How is translation regulated?
By promoter regions, enhancers, and transcription factors
Where are promoter regions located?
Near the beginning of a gene
RNA polymerase
Enzymes that transcribe genes to mRNA and attaches to promoter regions along w/ transcription factors
Enhancers
Regulatory sequences of DNA
Where are enhancers located?
Away from the gene
What do transcription factors do?
Bind to enhancer region which interacts and activates the promoter region
What are transcription factors?
Regulatory binding proteins
What can different transcription factors do?
Activate or repress transcription by interacting w/ each other, other proteins, and RNA polymerase
What do promoters, enhancers, and regulatory proteins do?
Allow a cell to respond to internal and external factors and control the genes that are transcribed
How can translation be further regulated?
By degradation of mRna by nuclease enzymes
How does regulation of transcription effect regulation of translation?
Regulation of transcription regulates the quantity of mRNA that’s produced which regulates rate of translation in a cell
What do nucleases do?
Break down mRNA to RNA nucleotides which can be recycled by cell to produce new mRNA molecules
Where are enhancers regions found?
Found upstream of the gene
- Before genetic sequences that are being transcribed
What do transcription factors do?
Bind to promoter regions and help regulate transcription of DNA
How long can mRNA be present in a human cells?
From minutes up to days before its broken down by nucleotides
What does the cell have to do in order to stop producing the protein in question?
It will need to stop making new mRNA and destroy the ones already circulating inside the cell
Epigenisis
Process by which a multicellular organism develops from zygote through a sequence of steps in which cells differentiate and organs form
What is epigensis a result of?
interactions between genes and their environments during their developments
Structure of mRNA
5’ is called the protective cap
3’ is called poly A tail
Epigenetics
The study of changes in an organism caused by modification of gene expression by epigenetic tags rather than changes in genetic code
- Changes phenotype but not genotype
Three layers of cell in a human embryo
- Ectoderm - Forms tissue like skin and brain
- Mesoderm - Forms tissues like skeleton and circulatory system
- Endoderm - Forms tissues like lungs and liver
Epigenetic tags
Chemical markers that attach to DNA or histone proteins and influence transcription of genes
- Usually stay in place during mitosis or meiosis
Genome
Includes all genetic info of an organism, all chromosomes, and mitochondrial and chloroplast DNA found in a cell
What are the exception of genomes and why?
Red blood cells - b/c no nuclues
Gamets - b/c only contain half the genetic material
What do patters of gene expression determine?
How a cell differentiates
Transcriptome
Refers to all RNA molecules transcribed at a specific time w/in a cellular organism
What do transcriptomes represent
Active genes and their expression w/in a cell or organism
Proteome
Complete set of proteins present in a cell or organism at a given time
What is different about proteomes of different cell types in same organisms?
They will be different b/c gene expression depends on the cell type
Methyl groups
Can act as epigenetic tags by attaching to promoter regions or histones
- Can attach to amino acids or histone proteins
What do methyl groups that are attached to cysteine nucleotides in prometer regions do?
Repress activity of prometer preventing gene from being transmitted
Methylation of histone proteins
Can cause transcription to be repressed, by DNA binding tighter to nucleotides, or activated by unwinding DNA from nucleotides
Epigenetic inheritance
beneficial as cell grows and results in daughter cells having same epigenetic tags as parent
What is similar about parent and daughter cells?
Daughter cells will express some as parent cell + carry out some functions
- Inherit phonotypic changes, epigenetic tags of parent cell
Epigenome
Has all epigenetic tags on DNA and histone proteins
Ex. of environment effecting epigenome
- Diet
- A person’s diet or their mothers while pregnant alters epigenome - Cigarette
- Epignetic changes due to exposure to cigarette smoke can lead to lung cancer - Air pollution
- like diesel fumes, are able to add/ remove methyl epigenetic tags from an individual’s epigenome
- Addition/ removal of epigenetic tags changes which genes are expressed
Removal of epigenetic tags
Most are removed during fertilization of egg and sperm in a process called reprogramming
- A small number are not removed
What allows gemets to be specialised cells?
The epigenome of the sperm and egg
Reprogramming
The reprogramming of epigenome of a zygote produces stem cells
Genomic imprinting
A process by which only one of the two inherited genes for a trait is expressed
- One copy of the gene is silenced by epigenetic tags during egg and sperm formaion
Monozygotic twins
Identical, a result of fertilization of one gene
- Clones and have same genome + v similar epigenomes
Epigenomes of monozygotic twins
Born with almost identical epigenomes, drastically change throughout life resulting in dif gene expression
Factors outside the cell that impact the pattern of gene expression
Presence of biochemical molecules which a cell metabolizes
- Gene expression in E.coli bacteria is impacted by presence/ absence of sugar lactose
Many Hormones form hormone receptors complexes w/in the cytoplasm of cell
- Hormone - receptors complex moves into nucleus where it binds to genes regulating transcription of DNA
What does the Lac operon do
regulates the transcription of the enzymes that are required for metabolism of lactose
What does the Lac operon consist of?
a promoter, an operator and a sequence of three genes
What happens when a lactose is present?
It binds to the repressor protein. The repressor protein changes shape, and is released from the operator
What happens when a lactose is absent?
a repressor protein binds to the operator and blocks RNA polymerase from transcribing the genes
