Ch. 16 and 17 Review Flashcards
What are the components of a chromosome?
- DNA
- Protein
In the 20th century, scientists believed what macromolecule encoded for genes?
Protein
When was the conformation of DNA known?
1950s via Watson and Crick
State Chargaff’s rule
A=Tor U
G= C
ratios of these purines and pyrimidines are equal
What did Watson and Crick conclude about DNA?
-DNA forms a HELIX with UNIFORM WIDTH (2nm)
-DNA has TWO polynucleotide chains
-The backbones are on the outside, bases on the inside
-H bonds hold bases together
How many bonds do the purines form?
Adenine forms 2 bonds, Guanine forms 3
DNA strands are _______
Antiparallel, strands run opposite from each other
Are DNA strands identical?
NO, they’re complimentary meaning 4 of nucleotide base pairs are possible
DNA must be copied because it encodes for what?
DNA encodes proteins and traits
How does the cell synthesize DNA
- Two strands separated
- Each strand used as a template to build new strands USING complementary base pairing
What happens to the original DNA?
It’s present in daughter cells but no longer intact. Semiconservative DNA.
Where does the energy for making DNA come from?
From the nucleotides bearing 3 phosphates. recall phosphates are covalently bonded, when broken they release a lot of energy. Nucleotide brings the energy NOT ATP.
DNA replication must be? What is the solution?
- accurate and efficient
occur at manly sites simultaneously
What is a replication bubble? Where are the forks?
Replication bubble on the origin of replication where new DNA is synthesized.
The forks are the ends of the bubble
What is needed to make DNA?
- 2 template strands
- Nucleotides
- Several enzymes and proteins (made during G1)
DNA polymerase adds to which DNA end?
3’ end
DNA is always built from 5’ to 3’
Which way are DNA template strands read?
3’ to 5’
Does DNA polymerase initiate polynucleotide synthesis?
NO, other enzymes do this using an RNA primer
What are the 1-2 steps of DNA replication?
- DNA helicase unzips DNA
- Single Strand Binding Protein stabilizes broken DNA strands (STICKY)
What are the steps for leading strand DNA synthesis?
3a. RNA primase makes RNA primer for DNA leading strand
3b. DNA polymerase moves towards the fork and makes DNA 5’ to 3’
What are the steps for lagging strand DNA synthesis?
4a. RNA Primase makes RNA primer for lagging strand
4b. DNA polymerase makes DNA away from the fork going 5’ to 3’
4c. Repeat steps previous steps (primer –> extend –> unwind)
lagging strand always moves away from the fork in many pieces called Okazaki fragments
How do you join Okazaki fragments?
via hydrolytic enzymes
enzymes remove RNA fragments and extend Okazaki fragment through the primer
Ligase will join the missing section of DNA via a covalent bond
Summarize the steps of DNA synthesis by concept only
- Helicase
- Single Strand Binding Protein
Leading Strand
3a. Primase
3b. Leading strand synthesis
Lagging strand
4a. Primase
4b. Lagging strand synthesis
5. primer placement
6. DNA ligase
What are the rules of DNA code?
- codons must occur in series
- codons cannot overlap
Transcription turns _____ into ______
DNA (a gene), RNA (mRNA)
Translation turns ______ into ______
RNA (mRNA), Protein
What is a codon
A specific 3 nucleotide sequence of DNA or RNA that corresponds to an amino acid
What are the stop codons? What are the start codons? Why is the start codon different?
Stop- UAA, UGA, UAG
Start- AUG which can also encode for amino acid methionine
Who uses genetic code?
Everyone!! Genetic code is universal
Compare replication and transcription in relation to gene copying
Replication- copies entire chromosome
Transcription- copies specific regions of DNA, often a single gene
How is a gene copied?
By complementary base pairing
Define transcription and how RNA polymerase is used
- Separates DNA strands
- ONE strand is chosen by RNA polymerase to be the template strand (the one that runs 3’ to 5’)
RNA polymerase
- adds to 3’ end (built 5’ to 3’)
- can initiate chain synthesis, no primer needed
- unwinds DNA, no helicase
What is a promoter?
Tells RNA polymerase which strand is the template strand and tells it where to start
What is a terminator?
Ends the transcription sequence and tells RNA Polymerase to stop
Is there semi-conservation in transcription?
NO, DNA is 100% conserved RNA polymerase unwinds and rewinds DNA
Where does transcription occur? What about translation?
Transcription- nucleus
Translation- cytosol (ribosomes)
Translation is different because mRNA is read _____ and builds proteins ______
Read- 5’ to 3’
Built- 5’ to 3’
How do tRNA’s recognize codons?
tRNA’s are L shaped
- carry a 3 nucleotide sequence that is the complement of the specific codon (anticodon)
- carry the amino acid encoded by the codon and recognize it
How is tRNA held together?
Intramolecular base pairs hyrdogen bond
If a tRNA had code AAG (anticodon), what would the codon be?
UUC
When an amino acid is attached to a tRNA, what does it become?
Aminoacyl tRNA
How is the correct amino acid joined to tRNA?
A special set of enzymes joins each tRNA with the correct amino acid by a covalent bond
tRNA synthetases
How many tRNA synthetases are there?
20, for every amino acid
Ribosomes contain a _____ for the mRNA to pass through
passage and building sites
What are the 3 things a ribosome does in translation?
- Facilitates base pairing between codon and anticodon
- Catalyzes the dehydration reaction and joins amino acids covalently
- Maintains the frame of reading
What is needed to make a protein?
- mRNA
- a SET of aminoacyl tRNA’s to complement all the different codons
- a ribosome
What are the basics of translation?
- decodes mRNA from 5’ to 3’
- builds polypeptide from N to C
- initiates at start codon AUG
- shifts along one codon at a time
- terminates at the stop codon
Where do tRNA’s and rRNA’s come from?
Transcription
What is a gene?
A region of DNA encoding either a polypeptide or an RNA (tRNA and rRNA)
