CH 7 - 8 Flashcards
Summarize process of making a protein from DNA (central dogma)
- Transcription
- use DNA sequence to make RNA molecule - RNA processing
- make edits to RNA molecule - Translation
- use RNA sequence to create sequential order of amino acids in protein
!!! Cells get identity from the proteins they make !!!
Compare and Contrast DNA and RNA
DNA
- transcribed into RNA
- all cells have the same DNA
- deoxyribose sugar
- thymine
- double stranded
RNA
- transcribed into protein
- cells differ in which and how much genes are turned into RNA and
- ribose sugar
- uracil
- single stranded
Classify the different types of RNA according to how they are transcribed, processed, and the distinct functions they have in the cell
- Ribosomal RNA (rRNA)
- made by RNA polymerase 1
- forms core of ribosome structure + catalyze protein synthesis - Messenger RNA (mRNA)
- made by RNA polymerase 2
- codes for proteins
3.Transfer RNA (tRNA)
- made by RNA polymerase 3
- adaptors between mRNA and amino acid during protein synthesis
Describe all the different types of processing that a pre-mRNA undergoes to become a mature mRNA
Splicing:
- removes introns and some exons (sequential order of exons are preserved)
- the rest of exons are stitched togeether
Editing: (textbook doesn’t talk about it)
5’ Capping:
- attaches a guanine nucleotide with a methyl group to the 5’ end of the RNA
3’ Polyadenylation:
- 3’ end is trimed by enzyme and then another enzyme addes a series of repeated adenine nucleotides to the “tail”
(capping and polyadenylation used to increase stability, facilitate export from nucleus to cytosol and is a biomarker to indicate mRNA)
Distinguish between introns and exons
Exons:
- codes for proteins
- used in transcription + translation
Introns:
- contains information on when and where a protein is expressed
- removed from mRNA during transcription
Provide a stepwise description of the sequence of events in mRNA translation initiation
- Recruit translation initaiton factors to mRNA to 5’ cap.
- Bring tRNA(that encodes for Methionine) and small ribosomal subunit to mRNA for scanning
- Large subunit joints once tRNA(methionine) base pairs with start codon
- certain tRNA can only base pair to specific codons (multiple codons can be bound to the same anticodon) - Second tRNA enters ribosome and the ribosome catalyzes new peptide bond
- Elongation
- Translation terminates once a release factor binds to the stop codon
Provide a detailed description of the translation elongation cycle
- new tRNA base pair
Charged tRNA carrying next AA enters A site via base-pairing - peptide bond formed
Carboxyl end of the polypeptide chain is uncoupled from tRNA at P site and forms peptide bond with amino acid on tRNA at A site - large hat shifts
large subunit of ribosome shifts to expose A site - small shoes shifts
Small subunit shifts 3 nucleotides and ejects spent tRNA
Compare and Contrast Transcription and translation
Transcription:
- occurs in the nucleus
- DNA to RNA
Translation:
- occurs in the ribosomes
- RNA to proteins
Both:
- both have designated start and end sites (transcriptional start / stop sites & start / end codon)
- both have directionality (5’ to 3’)
Describe how transcriptional control leads to the unique protein composition of each cell type
Each cell has specific composition of mRNAs and proteins that support its unique function!
This specific composition is attained by introns which code for what, when, and where RNAs for specific proteins are transcribed. (This is called transcriptional control)
Define transcription factor and discuss how transcription factors regulate the level of transcription at each gene by recruiting RNA polymerases
Transcription factor:
proteins that assemble on promoters of genes near (or far from) the start site of transcription and load the RNA polymerase in the correct position
Promoter:
DNA sequence that initiates gene transcription; includes sequences recognized by RNA polymerase and accessory proteins (transcription start site)
TATA box:
- DNA recognition sequence for first general transcription factor that binds to promoter
How do they regulate the level of transcription at each gene by recruiting RNA polymerase?
- allow gene expression to be adjusted in response to external signals (ex. nutrients)
- RNA polymerase 2 (DNA-specific enzyme) requires general transcription factors
List all the ways that protein production can be controlled in eukaryotes
- Transcriptional control
- when and how often a gene is transcribed - RNA processing control
- how RNA transcript is spliced / processed - mRNA transport + localization
- which mRNAs are exported from nucleus to cytosol - mRNA degradation control
- how quickly certain mRNA molecules degraded - translation control
- which mRNAs are translated into protein by ribosomes - protein degradation control
- how rapidly specific proteins are destroyed after they have been made - protein activity control
Discuss how transcription factors interact with chromatin-remodeling complexes to promote or inhibit transcription
Transcription regulators initiate transcription by recruiting chromain-modifying proteins:
- histone acetyltransferase adds acetyl to specific histone groups to serve as binding sites for proteins that stimulate transcription initiation
- histone deacetylases (removes acetyl group to histone tail and therefore reduces effiicency of transcription initation)
- chromatin remodeling complexes render DNA more accessible in nucleosome than others.
Describe how transcriptional control allows a cell to make complex biological decisions
- Generating specialized cell types
- all cells must turn genes on or off in response to signals in environment
- transcriptional control is used to form organized arrays of differentiated cell types - Eukaryotic genes are controlled by combinations of transcription regulators:
- Transcription regulators work together in a “committee” of regulator proteins that direct the assembly of the mediator, chromatin-remodeling complex, histone modifiying enzymes, general transcription factors, and ultimately RNA polymerase.
Identify features present in an mRNA that allow post-transcriptional regulation of gene expression
- MicroRNAs
control gene expression by base-pairing with specific mRNAS and inhibit stability and translation (targets complementary mRNA molecule for destruction: more extensive complementarity –> rapid degradation) - extra 5’ start sites:
impacts mRNA translation by making loading difficult: tangled up conformation or ribosomal unit falls off before reaching a functional start codon (inhibits translation)
- cell can inactivate repressor to initiate translation of mRNA (exposes functional start codon) - 3’ untranslated region:
- contains instruction about mRNA stability and is a target for degradation
Discuss how one can exploit transcription factor biology for cell and tissue engineering
Formation of entire organ can be triggered by single transcription regulator
- master regulators function like transcriptional regulators: controls the expression of multiple genes by binding to DNA sequences in regulator regions
- The genes regulated by the master regulator also encode for additional transcription regulators that also control expression of other genes.
- Mutations in master regulators can cause a cascade of events that impact the formation of an organized group of many different types of cells
