Unit 10 Flashcards
How do you go from DNA to a protein?
DNA –> RNA –> protein
Transcription
DNA sequence is rewritten as message RNA (mRNA)
Translation
mRNA is used to build a polypeptide (protein) from amino acids at a ribosome
Where is DNA transcribed in a prokaryote?
cytoplasm
Why does a prokaryote transcribe DNA in the cytoplasm
it has no nucleus
Where is DNA transcribed in a eukaryote?
nucleus
How many steps are there for transcription?
3
What are the steps of transcription? (3)
- Initiation
- Elongation
- Termination
Initiation (Transcription)
RNA polymerase recognizes a starting sequence on a gene (promoter) and unzips DNA
RNA polymerase
enzyme that catalyzes the reactions of transcription
promoter sequence (2)
- is a DNA sequence that defines where transcription begins
- defines the direction of transcription and indicated which DNA strand and gene will be transcribed
Elongation (Transcription)
RNA polymerase reads DNA coding region and uses ribonuclease to make a complementary strand of mRNA
What is the direction of elongation?
5’ to 3’
Termination (Transcription)
mRNA and RNA polymerase detach at termination DNA sequence
What is RNA that has been transcribed called?
messenger RNA (mRNA)
Which DNA strand is transcribed?
antisense strand
antisense strand
template for transcription (transcribed)
sense strand
coding DNA/gene (not transcribed)
How is the antisense strand transcribed? (2)
- using complementary base pairing
- base sequence of mRNA is the same as the sense strand (U replaces T)
What must happen in eukaryotes before translation?
mRNA must be processed/modified
RNA processing is… (3)
1) addition fo 5’ end cap
2) Addition of 3’ end poly (A) tail
3) Splicing
Splicing
removed from DNA regions that don’t codes for protein
What happens in the step of splicing?
introns are cut out of mRNA and exons are joined together to form a coding sequence
intron
DNA or RNA that doesn’t code for protein
extron
DNA or RNA base sequence that directly codes for proteins
alternative splicing
producing multiple RNA transcripts by joining different splice/cut sites
What is the result of splicing mRNA? (2)
- it increases the number of different proteins an organism can produce
- in eukaryotes, alternative splicing is more efficient because information can be stored economically
pre-mRNA
exons and introns
mature mRNA
exons only
ribonucleotides
RNA nucleotides with ribose
Why is transcription regulated?
so cells can only make protein they need
What are characteristics of genes in transcription? (2)
- types of proteins determines a cell’s characteristics
- most genes in a cell are turned off at any one time
gene expression (2)
- using a gene to make protein
- requires making specific mRNA and using mRNA to build polypeptides/proteins
What are factors that can impact gene expression? (2)
- temperature
- hormones
How do factors regulate gene expression?
regulating transcription
What does regulation of transcription orchestrate?
cells differentiation and development in multicellular organisms
What are factors that regulate transcription in eukaryotes? (3)
1) Transcription factors and non-coding DNA Sequences
2) DNA methylation
3) histone-protein modification
transcription factors (3)
- proteins that ↑ or ↓ decrease transcription rate by regulating binding of RNA polymerase to promoter
- some factors bind to promoter directly
- transcription can’t be initiated without certain factors
What transcription factors don’t bind the promoter? (2)
- activator proteins
- repressor proteins
activator proteins
bind to enhancer sequences (↑ rate of transcription)
repressor proteins
bind to silence sequences (↓ rate of transcription)
Where are enhancer and silencer sequences not located? (2)
- in a gene
- in non-coding DNA
What happens when a transcription factor binds to a promoter?
transcription at moderate levels
What happens when transcription factors bind to promoter and activators bind to enhancers?
the gene is transcribed at higher rates
What happens when transcription factors bind to promoter and repressors bind to silencer?
gene is transcribed at lower rates
DNA methylation
methyl groups (CH3) are added to DNA
What does methylation do?
- inhibits the binding of transcription factors and activators and decrease transcription/gene expression
nucleosomes
DNA wrapped around histone proteins for packing
Why do nucleosomes regulate transcription?
- DNA is inaccessible to transcription factors and RNA polymerase
In what case can binding occur with nucleosomes?
chemically modifying the histones forces nucleosome unwinding and allows binding
Epigenetics (2)
- study of changes to DNA that alter gene expression without changing DNA sequence
- some epigenetic changes can be inherited
What are some examples of epigenetics?
methylation and histone modification
What does translation build?
a primary structure
primary structure
amino aid sequence of a protein
What is an example of a product of translation?
enzymes that are used to speed up the process of transcription and translation
polypeptide
a sequence of amino acids
How does genetic information flow from mRNA to protein? (2)
- triplet code
- codon
Triplet code
groups of 3 bases
codon (2)
- a group of 3 base that does for one amino acid in a protein
- code for the same amino acids
The genetic code is… (2)
- universal
- degenerate
universal
living thing use the same bases, codons and amino acids
degenerate
same amino acid may be coded for by more than one codon, reduces impact of mutation
How do you read mRNA to determine the amino acid sequence? (3)
1) Scan the mRNA to find the START CODON
2) Continue reading codons and adding amino acids
3) Continue adding amino acids until you reach the STOP CODON
What is the start codon?
AUG
How many stop codons are there?
3
transfer RNA (tRNA)
read codons on mRNA and bring amino acid to the ribosome
What is on tRNA? (4)
- attached amino acid
- anticodon
- hydrogen bonds
- tRNA activating enzyme
attached amino acid to tRNA
specified by bound codon
anticodon on tRNA
is nucleotides that bind to mRNA codon using complementary base pairing
hydrogen bonding on tRNA
holds strands together/provide structure
tRNA activating enzyme (2)
- uses ATP to attach new amino acid to tRNA
- there are 20 of these enzymes that correspond to the 20 amino acids
What does a ribosome compose of? (4)
- large subunit
- small subunit
- ribosomal RNA (rRNA)
- proteins
Where is the mRNA binding site?
the small subunit
What holds the tRNA and mRNA together during translation?
the ribosomal subunits
At how many sites does a ribosome bind to mRNA?
3
What are the three binding sites on DNA?
- A-site
- P-site
- E-site
A-site
where incoming tRNA anticodon binds mRNA codon
P-site
where tRNA sits with the growing polypeptide chain
E-site
where tRNA without amino acid
resides before being released
How many types of ribosomes are there?
3
What are the types of ribosomes? (3)
- bound ribosomes
- polysomes
- free ribosomes
Bound ribosomes (2)
- on Rough ER
- make protein for export
Polysomes
many free ribosomes working on the same mRNA to complete translation more efficiently
Free ribosomes
make proteins for the cell
What are the steps of translation? (3)
1) Initiation
2) Elongation
3) Termination
Initiation (Translation) (2)
1) mRNA binds to small subunit and methionine tRNA binds to start codon
2) Large subunit binds with start tRNA in the P site. The A-site is aligned with 2nd mRNA codon.
Elongation (Translation) (5)
1) A site holds tRNA with next amino acid to be added
2) peptide bond is formed between the amino acid of the A site and polypeptide at the P site
3) polypeptide is transferred to the tRNA in the A site
4) Ribosome moves so the tRNA with the polypeptide in the A site moves to the P site
5) The tRNA without an amino acid moves to E site and leaves the ribosome
Termination (Translation) (3)
1) Ribosome reaches stop codon
2) A release factor binds in the A site causing the disassembly of the ribosome subunits
3) Polypeptide is released
What is the direction of translation?
The ribosome moves along the mRNA strand in the 5’ to 3’ direction
gene transfer (2)
- placement of new genes into an organism’s genome
- possible because the genetic code is universal
What is the result of inserting new genes?
making new proteins
How many steps are there of gene transfer?
4
What are the steps of gene transfer? (5)
1) Plasmids are removed from bacteria
2) Plasmid is cut using restriction endonuclease & the gene for transfer is cut out using the same restriction endonuclease
3) Desired gene is added to opened plasmid
4) DNA ligase covalently bonds DNA fragments
5) Recombinant plasmid is placed into a host cell
plasmid (2)
- small, circular DNA molecule in bacteria that doesn’t include essential genes
- used to carry new genes into cells because they can replicate on their own and produce proteins
restriction endonuclease
break covalent bonds between nucleotides at specific recognition sequences
sticky ends
single-stranded complementary ends
What is the same restriction endonuclease used for?
to cut the target gene out of the organism’s genome
What does using the same restriction endonuclease result in?
complementary sticky ends
What can complementary sticky ends do?
hydrogen bond to make recombinant DNA
recombinant DNA
DNA with a different combination of genes than it had originally
DNA ligase
enzyme that covalently bonds DNA strands together (phosphodiester bond)
What typically is the host cell? (2)
- bacterium
- yeast
What will the host cell do after the gene transfer is completed?
The host cell will transcribe and then translate the gene of interest to make the desired protein
Why is gene transfer possible?
due to universality of genetic code
antibiotic selection
placing antibiotic resistance gene in plasmids to identify which cells have recombinant DNA
making human insulin
gene transfer is used to insert the human gene for insulin into bacteria
What happens when insulin is successfully transferred into a bacteria cell?
Bacteria produce insulin protein and the insulin is extracted from the cells
gene therapy
inserting genes into cells to treat hereditary diseases by replacing defective alleles/genes
How does gene therapy work? (2)
- Cells are removed and a virus introduces a functional copy of the defective gene
- Cells are transplanted back that can make the missing protein and restore normal health
What is an example of gene therapy in humans? (2)
- treatment of adenosine deaminase (ADA) deficiency
- Individuals who have had gene therapy have shown a steady increase in the levels of ADA in their cells
What are some applications of gene transfer within the filed of genetic engineering? (4)
1) industry/medicine: produce large quantities of proteins such as insulin
2) gene therapies: repair faulty genes
3) genetically modified organisms: nutrient rich types
4) transgenic animals for scientific research
genetic modification
DNA of an organism is artificially changed such that some characteristic of the organism is changed
What are the benefits of GM crops for human health? (3)
- can improve nutritional standards, by incorporating genes for proteins or vitamins
- crops could be produced that lack toxins or allergens
- crops could contain edible vaccines to provide natural disease resistance
What are the risks of GM crops for human health? (3)
- Not all GM foods are labelled, making informed decisions difficult for consumers
- antibiotic resistance genes could spread to «pathogenic» bacteria
- transferred genes could cause unexpected problems/allergies
What is an example of a GM crop meant to improve human health?
golden rice: enriched with beta-carotene which is converted into vitamin A to prevent blindness
What are the benefits of GM crops for economics? (3)
- pest-resistant crops cause less spraying of insecticides/pesticides
- include genes to increase variety of growing locations drought
- genes to slow the rate of spoiling
What are the risks of GM crops for economics? (3)
- non-target organisms can be affected
- genes for herbicide resistance could spread to wild
- Patents restrict seed usage and create high prices for use
What are some examples of a GM crop that comes with economic benefits? (2)
- insecticide sweet corn
- salt-resistant tomatoes
What are the benefits of GM crops for the environment? (2)
- pest-resistant crops result in less spraying of insecticides/pesticides
- include genes to increase variety of growing locations / can grow in threatened conditions
What are the risks of GM crops for the environment? (2)
- non-target organisms can be affected
- genes transferred to crop plants to make them herbicide resistant could spread to wild
What is a named example of a GM crop that comes with environmental benefits?
Bt potatoes
Bt corn (3)
- genetically modified by transferring a gene from a bacterium to corn plants (Bt gene)
- produces a protein (Bt toxin) lethal to insects
- Bt corn is lethal to the European corn borer which eats corn crops
What is the concern of Bt corn?
monarch butterflies eating Bt corn pollen could be harmed/die
What was the outcome of the study on Bt corn?
no significant increase in mortality when monarch larva were placed in or near an actual Bt corn field
What are the benefits of Bt corn? (2)
- corn borer/insect pest is killed by Bt toxin increasing crop production
- less pesticides/fertilizers/chemicals needed so better for environment
What are the harmful effects of Bt corn?
non-target insects may be killed as well
transgenic animal (2)
- gene transfer is used to deliberately modify the genome of an animal
- Recombinant DNA must be inserted into all cells including germ cells
germ cells
cells that give rise to gametes
