Unit 5: Protein Synthesis Flashcards
Define
Transcription
Using DNA as a template to make mRNA
Define
Translation
Production of polypeptides using the DNA code (copied into molecule of mRNA)
Explain why DNA has a template and coding strand
DNA has two strands; each gene is encoded on only one, while the other helps stabilize the molecule and make mRNA
Compare the template and coding strands
- *Coding**: Carries the information for making the gene product
- *Template**: Complementary to the coding strand; is used to make the mRNA
The mRNA sequence most resembles…
The coding strand
Outline the process of
Transcription: Initiation (Euks)
- Specific transcription factors bind to the promoter
- RNA Polymerase binds to the promoter
Define
Promoter
A segment of DNA before a gene which is the “docking area” for RNA polymerase to bind
Define
Transcription factors
Proteins that bind to the promoter and can either increase or decrease the RNA polymerases’ ability to bind
Outline the process of
Transcription: Elongation
RNA polymerase separates the DNA and adds complementary base pairs to the template strand
Define
RNA polymerase
The enzyme used during transcription to make mRNA
In which direction is mRNA made?
5’ to 3’
Importance of
5’ cap
A chemical modification to the 5’ end of mRNA that is being formed, which prevents nuclear enzymes from breaking down the mRNA as it is being made
Outline the process of
Transcription: Termination
RNA polymerase reaches terminator sequence on DNA, causing the DNA, polymerase, and mRNA to dissociate
Importance of
Poly-A tail
Sequence of many adenines that is added after eukaryotic transcription is complete, which allows the mRNA to exit the nucleus
List
Eukaryotic modifications to mRNA
- 5’ cap
- Poly-A tail
- Splicing
Define
Exon
Segments of a gene that are expressed
Define
Intron
Segments of a gene that are not expressed; must be spliced out to make functional gene product
Define
Splicing
Removal of introns and re-joining of eons to make a mature mRNA
What is alternative splicing?
Some genes contain multiple exons, which can be rearranged in different ways to produce multiple unique proteins from the same gene (WHAT?! SO COOL!)
Compare
Transcription in Proks vs. Euks
- Prokaryotes have one promoter that controls multiple related genes, which may be regulated by an operon
- Related functional genes may be on different chromosomes in eukaryotes but may be regulated by transcription factors so their production is coordinated
Define
Operon
In prokaryotes ONLY
A segment of the genome that has one promoter, an operator, and several functionally related genes
Define
Operator
Part of the prokaryotic operon that can bind to a repressor or inducer, like a “switch” to control transcription
Define
Stem cell
In multicellular eukaryotes, cells that are undifferentiated
Can divide to produce cell types that are different by changing gene expression
Define
Differentiation
When stem cells divide, the daughter cells may turn off specific genes (based on cell signaling) and express only tissue-specific genes
Largely controlled by which transcription factors are present or made
Define
Epigenetics
Modifications to gene expression without modifying the DNA sequence
Examples of
Epigenetic control
DNA methylation (prevents RNA polymerase from binding) Histone modification (histones may tighten and become less accessible or loosen and become more accessible)
Why is transcription regulated?
Once mRNA is produced, translation isn’t as highly regulated. Regulating transcription ensures only the genes that the cell needs are expressed and prevents wasting material on unnecessary genes.
Define
The lac operon
In prokaryotes, several genes control for the ability to use lactose for ATP production. They are all controlled by a single operator.
What happens to the lac operon when lactose is absent?
The lac operator has a repressor bound, which prevents production of the associated genes
What happens to the lac operon when lactose is present?
Allolactose (isomer of lactose) binds to the lac repressor and prevents it from binding to the operator. RNA Polymerase can then move past the operator to express the lac genes
Describe
tRNA
A single strand of RNA which loops back onto itself. At one end there is a region that binds an amino acid. At the other end of the folded RNA there is an area that contains a unique sequence of nucleotides, called the anticodon
How many tRNAs are there? Why?
64, each with a unique anticodon (anticodon = 3 nucleotides, each of which can be either A, U, C, or G) making 43 possible anticodons
How many amino acids are there?
About 20
Define
The genetic code
The specific amino acid coded for by each possible codon
The genetic code is considered…
- Nearly universal and 2. Redundant
What determines the genetic code?
The enzyme that joins the amino acid and tRNA (called aminoacyl tRNA synthetase, which you don’t have to know but is still impressive). Changes to this enzyme will change which amino acid the tRNA brings to the ribosome
Describe
Ribosomal structure
Two subunits, each made of proteins and RNA (called ribosomal RNA).
The small subunit is smaller.
The large subunit is larger.
Eukaryotic large and small ribosomal subunits are larger than the ribosomal subunits found in prokaryotes (and in mitochondria and chloroplasts)
Describe
Translation: Initiation
- Small ribosomal subunit binds to the 5’ end of mRNA
- Subunit reads mRNA sequences until it finds an A-U-G
- tRNA with the anticodon U-A-C joins; This particular tRNA carries the amino acid methionine
- A large ribosomal subunit binds to the small ribosomal subunit/tRNA/mRNA combination
Define
Codon
Three nucleotide bases on mRNA
Describe
Translation: Elongation
- tRNA brings amino acid to ribosome (determined by the mRNA codon being complementary to the tRNA anticodon)
- Peptide bond forms between the new amino acid and the growing polypeptide
- tRNA (without amino acid) leaves ribosome
Describe
Translation: Termination
- Ribosome continues along mRNA until a stop codon is reached
- Release factors bind
- mRNA, tRNAs, polypeptide, and ribosomal subunits all dissociate
List
Three types of substitution mutation
Nonsense
Missense
Silent
Describe
Nonsense mutation
A change to DNA that results in an mRNA coding for a stop codon instead of an amino acid
Describe
Missense mutation
A change to DNA that results in an mRNA coding for a different amino acid
Describe
Silent mutation
A change to DNA that results in an mRNA coding for the same amino acid as the original DNA
What causes
Frameshift mutations
Insertion or deletion of nucleotides (not in multiples of 3)
Describe
Frameshift mutations
A change in DNA that results in an mRNA whose reading frame differs from the original. All downstream amino acids are affected.
Ex:
Normal: “THE FAT CAT RAN”
Mutated (delete E): “THF ATC ATR AN”
In which direction are polypeptides made?
N terminus to C terminus
Backbone: NH2-C-C-…..-N-C-COOH
Define
Mutagen
Any agent that causes changes to DNA
List
Mutagens
Certain chemicals (carcinogens), radiation, certain viruses
Define
Biotechnology
The intentional use of biological processes for other purposes
Purpose of
PCR
Polymerase chain reaction; makes multiple copies of a segment of DNA
Outline the process of
PCR
- DNA is heated to separate strands
- Primers are added, which bind to each side of the DNA segment of interest
- DNA polymerases are added, which replicates DNA strand
- Repeated cycles of heating and cooling each double the amount of DNA present
Purpose of
Gel electrophoresis
Separate DNA segments by length
Uses of
Gel electrophoresis
DNA profiling, paternity testing
Outline
Genetic modification
- A gene from one organism (donor) is inserted into the embryo of another organism (recipient).
- The gene of interest from the donor is combined with a functional promoter from the recipient.
- This is then inserted into the genome. If expressed, the recipient is transgenic.
Define
GMO
Genetically modified organism; an organism whose genes were modified for human benefit.
Examples of
GMOs
- Genetically modified plants: Insect-resistant crops; pesticide resistant crops; Nutrient fortified crops.
- GM animals: Glofish; pharmaceutical-milking animals;
- GM bacteria for the production of pharmaceuticals, vaccines, antibodies, etc
