Replication
Draw and explain semiconservative replication
See slide 33-34 of DNA1
Name 2 differences between DNA and RNA
deoxyribose vs. ribose
double stranded vs. single stranded
A-T vs. A-U
What is a codon?
A sequence of three nucleotides ("triplets") on mRNA that codes for a specific amino acid
True or false: Mutations in somatic cells can be passed on to the next generation.
False
Mutations that occur in germ cells are passed on to the next generation
Where is DNA found in an animal cell? Draw and label a diagram of a cell.
Cell with nucleus and mitochondria labeled
During replication, what structural feature of DNA causes one strand to be built continuously while the other is built in fragments?
The sugar phosphate backbone is anti-parallel (one runs in 5'-3' direction and the other in 3'-5')
During transcription, which base replaces thymine?
Uracil
What is the role of tRNA in translation?
tRNA carries amino acids to the ribosome and matches them to the codons on the mRNA using its anticodon.
Original mRNA codon sequence: 5′–AUG GCU UAC–3′
Mutation: 5′–AUG GCC UAC–3′
Which codon changed?
Identify the mutation type.
Will the protein sequence change?
GCU → GCC
Silent
No, the protein sequence remains: Met – Ala – Tyr
___________ is repeated cycles of heating and cooling used to make copies of a specific DNA sequence.
Polymerase Chain Reaction (PCR)
What are the 7 steps of DNA replication?
1. Helicase unzips parental DNA (binding proteins keep DNA unzipped)
2. Primase adds RNA primers
3. Polymerase III adds based in 5'-3' direction starting at the primer
4. Polymerase I removed RNA primer and replaces with DNA nucleotides
5. Ligase glues new DNA
6. Polymerase III fixes mistakes
7. Hydrogen bonds between nucleotides are formed
What is the difference between the sense and anti-sense strand?
Sense: strand not being coded
Anti-sense: template strand
________ are spliced out by spliceosomes before the mRNA is translated
Introns - sections of non-coding DNA that interrupt the coding sections (exons) of the gene
What are the two types of mutagens? Explain how each causes DNA mutations
Physical: breaks nucleotide sequence, causing random changes
Chemical: enters cell nucleus and causes permanent changes in genetic material by reacting with DNA
What is a vector?
A way of introducing foreign DNA into a genome of a living cell.
e.g. viruses and plasmids are used as vectors
Draw and explain the difference between the leading and lagging strand.
Leading strand: made continuously towards replication fork
Lagging strand: made in Okazaki fragments away from the replication fork
What are the steps of transcription?
1. RNA Polymerase binds to open the double helix at the beginning of the gene
2. It recognizes the starting (promoter) sequence
3. RNA Polymerase unwinds the DNA
4. RNA Polymerase builds mRNA strand in 5'-3' direction using DNA as a template
5. RNA Polymerase reached termination sequence and disconnects
What are the steps of translation?
1. Ribosome binds to mRNA (begins at the START codon, AUG)
2. Reads 3 bases of RNA at a time (a reading frame) in 5'-3' direction
3. tRNA carriers correct amino acid to the ribosome (tRNA has anticodon that allows it to bind to mRNA)
4. Ribosome shifts to next codon
5. Next corresponding tRNA attaches with the amino acid (2 tRNAs can attach at one time)
6. A peptide bonds forms between the amino acids
7. Continues until STOP codon is reached
8. Release factor helps remove ribosome from RNA
Explain why a nonsense mutation often has a more severe effect on a protein than a missense mutation.
A nonsense mutation creates a premature stop codon, producing a shortened, usually nonfunctional protein. A missense mutation changes one amino acid, which may or may not affect function.
Explain the process of how recombinant DNA is made
1. Find the gene using DNA probes
2. DNA cut suing restriction enzymes
3. Sticky ends created
4. The other DNA is cut with the same restriction enzyme (so similar sticky ends) and inserted
5. DNA ligase reattaches new components
6. Now we have recombinant DNA
If a newly synthesized DNA strand contains many mismatched bases, the enzyme ___________ likely failed its function of ____________.
DNA Polymerase III, proofreading
A mutation causes RNA polymerase to bind too tightly to DNA and never detach. Which stage of transcription would this prevent?
Termination
Explain why prokaryotic translation can begin before transcription is complete, but eukaryotic translation cannot.
In prokaryotes, transcription and translation both occur in the cytoplasm, allowing ribosomes to start translating mRNA as it’s being made.
In eukaryotes, transcription occurs in the nucleus and mRNA must be processed and exported to the cytoplasm before translation.
Explain why insertions or deletions that are multiples of three nucleotides are less disruptive than single-nucleotide insertions or deletions.
They add or remove whole codons, preserving the reading frame, so only specific amino acids are changed rather than all downstream amino acids.
You are given a DNA sample containing fragments of the following sizes (in base pairs):
500 bp, 1200 bp, 800 bp, 200 bp
Draw a diagram of an agarose gel showing the relative positions of these DNA fragments after electrophoresis.
Smallest fragment should be farthest from the well.
Top --> Bottom
1200 bp
800 bp
500 bp
200 bp