Unit 10-Molecular Genetics Flashcards
DNA structure
nitrogenous bases
- T,G,C,A
backbone
- sugar phosphate
What type of polymer and monomer is DNA and RNA
Polymer = nucleic acids Monomer = nucleotides
The nucleotides are joined together by what
Covalent bonds between the sugar of one and the phosphate of the other
This creates the sugar phosphate backbone
Along a strand of a double helix is the nucleotide sequence GGCATAGGT. what is the complementary sequence for the other DNA strand
CCGTATCCA
Define semi conservative model
A model of DNA replication that half of the parental molecule is maintained (conserved) in each daughter molecule
The DNA double helix separates and each half acts as a template while free nucleuotides come in and attach in the appropriate sequence to the new daughter strand (synthesis of the complementary stand!)
How does complementary base pairing make possible the replication of DNA
When the two strands of the double helix separate, free nucleotides can base pair along each strand leading to the synthesis of new complementary strands
Replication of a DNA molecule begins at _______
Special sites called origins of replication
What enzyme is used to create replication bubbles (separate the parental strands)
DNA helicase separates the the parental strands to create two forks
DNA replication proceeds in two directions at many sites simultaneously how does this work
The leading strand opens in the 3’ to 5’ direction (top strand)
Lagging strand opens in the 5’ to 3’ direction (bottom strand)
On the leading strand in what direction do you read to form the daughter strand
What direction is it synthesized
3 to 5 direction
5 to 3 direction
What is the overall direction of replication
To the left
From the tip of the fork to the point where it closes
What is DNA polymerase
The enzymes that link DNA nucleotides to a growing daughter strand
Where does DNA polymerase add nucleotides
ONLY at the 3’ end of the strand!!
Never the 5’
Therefore!
A daughter DNA strand can grow only in the 5’ to 3’ direction
Which daughter strand can be synthesized continuously
Which daughter strand cannot and why
The daughter strand that starts at the 5’ and goes to the 3’ TOWRDS the point in which the fork meets
(Continuous)
The daughter strand that starts at the 5’ and goes to the 3’ away from the point the fork meets needs to be synthesized in short pieces
What is DNA Ligase
An enzyme that works to link the pieces together of the second daughter strand that was NOT done continuously
These fragments are called Okazaki fragments
DNA strands are ___
Antiparallel
On the lagging strand in what direction do you read the DNA
In what direction is it synthesized
3’ to 5’
5’ to 3’
What is the function of DNA polymerase in DNA replication
As free nucleotides base pair to a parallel DNA strand the enzyme covalently bonds them to the 3’ end of a growing daughter strand
What is the 3’ prime and 5’ prime
The primed numbers refer to the carbon atoms of the nucleotide sugars
At one end of each DNA strand the sugars 3’ carbon atoms is attached to an -OH group and at the other end the sugars 5’ carbon is attached to a phosphate group
What are the two main stages of DNA replication and synthesis
Transcription
- the synthesis of RNA under the direction of DNA
Translation
- the synthesis of protein under the direction of RNA
What are the functions of transcription and translation
Transcription is the transfer of information from DNA to RNA.
Translation is the use of the information in RNA to make a polypeptide
Are both stands of the DNA transcribed
No! Only one is transcribed
The template strand
The DNA template strand AAACCGGCAAAA is transcribed into what code for RNA
UUUGGCCGUUUU
What is a triplet code
The genetic instructions for the amino acid sequence of a polypeptide chain are written in DNA and RNA as a series of non overlapping three base “words” called codons!
What is the genetic code
The set of rules that relate codons in RNA to amino acids in proteins
What are the three transcripts of RNA synthesis
rRNA
mRNA
tRNA
What codon codes for Met which starts the sequence
AUG
What three codons code for stop
UAA
UAG
UGA
What is a promoter?
What molecule binds to it
A promoter is a specific nucleotide sequence at the start of a gene where sigma factor and RNA polymerase attach and begin transcription
Define promoter
A specific binding site for a protein called sigma factor
What is RNA polymerase
The RNA nucleotides are linked by this enzyme
What are the three phases of transcription
Initiation
Elongation
Termination
Explain initiation
The attachment of RNA polymerase to the promoter and the start of RNA synthesis
Sigma factor binds to specific DNA and RNA polymerase binds to the sigma factor
Explain elongation
The RNA grows longer
The RNA strand peels away from its DNA template allowing the two separated DNA strands come back together
Explain the terminator phase
The RNA polymerase reaches a sequence of bases in the DNA template called the terminator
Signals the end of the gene and the polymerase molecule detaches
The kind of RNA that encodes amino acid sequence is called __
Messenger RNA (mRNA)
It conveys genetic messages from DNA to the translation machinery of the cell
mRNA is transcribed from DNA and then mRNA translates to polypeptides
What does the 5’ cap and poly a tail do for the mRNA
5’ cap
- protects the mRNA before exiting the nucleus
- facilitates ribosome binding
Poly A tail
- protects the mRNA before exiting the nucleus
- signals transport to cytoplasm
Are not translated into proteins !
What else needs to be done to the RNA before leaving the nucleus
Cut the introns out and bind together the exons
Called RNA splicing
Why are most eukaryotic genes longer then the mRNA that leaves the nucleus
These genes have introns
Which are no coding sequence of nucleotides that are spliced out of the initial RNA transcript to produce mRNA
Define transfer RNA (tRNA)
To convert words of nucleic acids (codons) to the amino acid words of proteins a cell employs a molecular interpreter a special type of RNA called tRNA
A quasi double helix
What do tRNA’s do
1) picks up the appropriate amino acids
2) recognize the appropriate codons in the mRNA
What is the anticodon
tRNA codes for an anticodon triplet that is complementary to a codon triplet on mRNA
How many tRNA molecules are there
61
What is an anticodon and what is its function
It is the base triplet of a tRNA molecule that couples the tRNA to a complementary codon in the mRNA
This is a key step in translating mRNA to a polypeptide
What is rRNA
Ribosomal rna
Used to position mRNA and tRNA close together to catalyst the synthesis of polypeptides
What are the two subunits of the ribosome
Small on the bottom
Large on the top
Between subunits mRNA binds
P site to the left
A site to the right
P and A site are tRNA binding sites
How does a ribosome facilitate protein synthesis
A ribosome holds mRNA and tRNA together and connects amino acids from the tRNA to the growing polypeptide chain
What are the three stages of translation
The same as transcription
Initiation
Elongation
Termination
What are the two steps of translation initiation
An mRNA molecule binds to a small subunit. A special initiator tRNA binds to the specific codon called the start codon
The initiator tRNA carries the amino acid Met and the anticodon UAC binds to the codon AUG
Then the large ribosomal unit binds to the Amal one and the initiator tRNA fits into the P site
What does the P site hold
What does the A site hold
The growing polypeptide
Vacant and ready for the next amino acid bearing tRNA
What are the three steps of translation elongation
Codon recognition
Peptide bond formation
Translocation
Explain codon recognition
The anticodon of an incoming tRNA molecule carrying its amino acid pairs with the mRNA codon in the A site of the ribosome
Explain peptide bond formation
The polypeptide speedster from the tRNA in the p site and attaches by a new peptide bond to the amino acid carried by the rRNA in the a site
The ribosome catalyzes formation of the peptide bond adding one more amino acid to the growing polypeptide chain
Explain translocation
The p site tRNA now leaves the ribosome and the ribosome translocates (moves) the remaining tRNA in the a site with the growing polypeptide to the p site
mRNA and tRNA stays bonded and moves as a unit
Then a new tRNA comes into the a site to translate the mRNA
Where does transcription occur
Where does translation occur
Nucleus
Cytoplasm
Define a mutation
Any change in the nucleotide sequence of DNA
Define a silent mutation
A substitution mutation that has no affect at all
The protein is the same
Define a missense mutation
A substitution mutation that does change the amino acid coding
Can have little or no affect if the new protein has similar properties as the original protein
Define nonsense mutations
A nucleotide substitution that leads to a harmful mutation
Change an amino acid codon into a stop codon
How could a single nucleotide substitution result in a different protein
It changes the reading frame
