Molecular Genetics (Lessons) Flashcards
Which two nitrogen bases are purines? Are they single or double ring?
A (Adenine) and G (Guanine), double-ringed
How are the sugar-phosphate backbones bonded to each other?
Through their nitrogen bases: hydrogen bonding.
Name the three differences between DNA and RNA
1 - type of sugar (deoxyribose/ribose)
2 - number of strands (double/single)
3 - nitrogen bases (thymine/uracil)
Which direction is new DNA built in?
5’ to 3’
What enzyme makes new DNA?
DNA polymerase III
When building new DNA, enzymes require a template strand and a starting point, called a _____.
Primer
What enzyme breaks the hydrogen bonds between bases and separates the DNA strands?
Helicase
What is the name of the molecule that prevents DNA from rewinding during replication?
Single-stranded binding proteins.
What are primers? What makes them? Where are they added?
Primers are short strands of RNA. Made with primate. Added to single strand at the 5’ end.
DNA can only be added in the ________ direction, but the newly formed lagging strand runs __________.
5’ to 3’, 3’ to 5’.
What is the name of the fragment type that DNA polymerase III uses to build up new DNA?
Okazaki Fragments
What enzyme joins together Okazaki fragments?
DNA ligase
Short, single stranded ends of DNA are called ______. As these shorten, the cell ages and dies.
Telomers.
What enzyme ‘checks’ for errors in DNA replication, and how?
DNA polymerase I, catches errors in base pairing by recognizing absence of hydrogen bonds
Describe transcription, in simple terms.
DNA is organized into segments called genes. RNA polymerase sees the TATAA box (promoter sequence) and copies DNA into mRNA.
Why can errors occur in transcription?
No proofreading (DNA polymerase I)
How does transcription end?
RNA polymerase reaches the terminator sequence (G’s, C’s, A’s). Pre-mRNA detaches.
pre-mRNA is processed in 3 steps before it leaves the nucleus. Name these steps.
1 - 5’ cap added.
2 - poly-A tail added
3 - spliceosomes remove introns (no coding sequences) and reconnect exons (coding sequences)
What two things are needed for TRANSLATION?
tRNA and ribosomes
What is an anticodon?
3 nucleotides that are complementary to the mRNA codon. Allows tRNA to stick to mRNA codon.
Ribosomes have three binding sites for tRNA. Name them and what they do.
P site: holds tRNA & amino acid chain
A site: ‘arrival’, holds the tRNA bringing next amino acid
E: ‘exit’, releases tRNA as ribosome shifts to read next codon.
Describe the initiation of translation.
mRNA reaches the cytoplasm and sticks to rRNA in the ribosome. Anticodon (complementary to start codon AUG) bonds to mRNA in the P-site
Describe the elongation process of translation in 3 steps.
1 - tRNA binds to mRNA codon in the A-site, chain transferred from P-site to A-site (peptide bond).
2 - Ribosome moves 3 nucleotides over to read next codon, newly exposed codon makes up empty A-site. tRNA from P-site —-> E-site.
3 - Process REPEATED.
Describe the termination process of translation
Elongation continues until stop codon is reached, preventing more amino acids from joining chain. Release factor frees chain, chain leaves ribosome and will take shape by folding.
Name three methods of gene regulation in eukaryotes, and explain each
1 - transcription control (block transcription)
2 - post transcriptional control (mRNA degrades, poly-A tail/5’ cap shorten. mRNA does not leave nucleus)
3 - post translational control (polypeptide degrades OR polypeptide folding is delayed)
How is gene expression regulated in prokaryotes?
Protein production is controlled ONLY by transcriptional regulation (on or off)
What is an operon?
Blocks of proteins that have been encoded together, as they are all needed for the same function or biochemical pathway.
Name the three regions of the operon and what they do.
1 - coding region (contains codons)
2 - promoter site (TATAA box - RNA polymerase binds)
3 - operator (DNA region that determines if transcription happens)
What is Lac Operon?
An operon that codes for LACTASE in bacteria like E. Coli. Breaks lactose into glucose and galactose for usable energy.
What two conditions must be met for lac operon to be activated?
low/absent glucose levels, and lots of lactose.
How does the lac operon function? Give both scenarios.
Lactose absent - lac repressor binds to the operator region. transcription blocked.
Lactose present - induced (allolactose) binds to lac repressor and forces it to leave, allowing transcription.
How do restriction enzymes work?
Cut DNA like molecular scissors at certain sequences (restriction site). Leaves ‘sticky ends’ of the DNA.
Describe how DNA is amplified using bacterial vectors.
Restriction enzymes cut open bacterial DNA (plasmid). Same striction enzyme cuts out DNA sequence of interest. Sequence inserted into plasmid, sticky ends base pair.
What does PCR stand for?
Polymerase Chain Reaction
Describe how PCR amplifies DNA
Target DNA heated to separate DNA strands. Cooled to body temperature, and primers are added to each DNA strand. Heated once again, activates DNA polymerase and attaches bases to primer sequence, making two identical strands. Cycle repeats.
Describe how gel electrophoresis can be used to analyze DNA.
Restriction enzymes cut DNA. DNA loaded into gel ‘wells’ at the negative end of the terminal. Electrical current activated, DNA moves towards positively charged cathode (smaller DNA segments travel farther, gel acts as a molecular strainer).
Name the three types of point mutations. Give examples, using the start code UGC (cysteine).
Nonsense mutation: UGA (stop)
Missense mutation: UGG (tryptophan)
Silent mutation: UGU (cysteine)
What are the two types of missense gene mutations? What does it mean?
Conservative (basic protein) and non-conservative (polar protein)
What are the two types of base substitution mutations?
Transition (one purines for another) and trans version (purines for a pyrimidine)
What is a frameshift mutation? What are the types?
A mutation that changes the reading frame of a nucleotide sequence. DNA can be INSERTED or DELETED (Insertion/deletion mutations)
Name the four types of chromosome mutations.
Deletion, duplication, insertion, translocation.
Why are chromosome mutations more serious than gene mutations?
Chromosomal mutations affect whole sets of genes, altering more genetic information and often having more serious effects.
