Lecture 08 Flashcards
The two business ends of tRNA
1) the anticodon forms hydrogen bonds with the mRNA codon
2) the 3’ end binds the amino acid specified by the mRNA codon
What controls gene expression in bacteria?
Oerson
What controls gene expression in more complex organisms?
transcription factors and links genome to environment
About how many transcription factors in humans
~2,000
What are the steps of transcription?
1) Initiation
2) Elongation
3) Termination
Transcription initiation
a cascade of transcription factors bind to the promoter region of a gene
-these open a pocket allowing the RNA polymerase to bind just in front of the start of the gene sequence
Transcription elongation
RNA polymerase reads the nucleotides on the template strand from 3’ to 5’ and creates an RNA molecule that looks like the coding strand
Transcription termination
occurs when sequences in the DNA prompt the RNA polymerase to fall off ending the transcript
Translation
the process of reading the mRNA base sequence and creating the amino acid sequence of a protein
-occurs on the ribosome
The genetic code
there are 64 codons, including:
- one start signal (AUG)
- three stop signals (UAA, UAG, and UGA)
Genome sequences orientation
From short p-arm to long q-arm and in a 5’ to 3’ direction
Forward and Reverse oriented gene transcript
- FWD oriented - its coding strand is on the plus strand of the genome sequence
- REV oriented - it’s on the minus strand
Protein-encoding gene controls and the two general processes
- Promoter sequence (mutations)
- Extra copies of gene
Processes
1) Chromatin remodeling = “on/off” switch
2) microRNAs = “Dimmer” switch
Chromatin remodeling - Three major types of small molecules that bind to histones (major role in gene expression)
Chromatin remodeling: transcription off –> (groups) transcription on
1) Acetyl group
2) Methyl groups
3) Phosphate groups
microRNAs
- Belong to a class of molecules called noncoding RNAs
- 21-22 bases long
- human genome ~1,000 distinct microRNAs that regulate at least 1/3 of the protein-encoding genes
What happens when a microRNA binds to a “target” mRNA
- It prevents translation
- It can also tag the mRNA for degradation
Maximizing genetic info
The 20,325 genes in the human genome encode ~100,000 mRNAs, which in turn specify more than a million proteins
the “genes in pieces” pattern of exons and introns and alternate splicing help to greatly expand the gene number
proteins > (outnumber) genes
Multifactorial traits
- caused by multiple factors including both genetic influences and environmental influences
- usually polygenic (influenced by many gene) w/ incomplete penetrance
Studying multifactorial traits - quantitative genetics
attempts to determine the relative contribution of genes versus environment (heritability) to the trait variation observed in a population (e.g., nature vs. nurture)
empiric risk
measures the probability that a trait will recur/occur based solely on observations
incidence
the rate at which a certain event occurs (e.g., new cases/year)
prevalence
the proportion or number of individuals who have a particular trait at a specific time (e.g., total cases)
heritability
estimates the proportion of the phenotype variation in a population due to genetic differences
