Molecular Genetics (Lessons)

Question 1

Which two nitrogen bases are purines? Are they single or double ring?

Answer 1

A (Adenine) and G (Guanine), double-ringed

Question 2

How are the sugar-phosphate backbones bonded to each other?

Answer 2

Through their nitrogen bases: hydrogen bonding.

Question 3

Name the three differences between DNA and RNA

Answer 3

1 - type of sugar (deoxyribose/ribose)
2 - number of strands (double/single)
3 - nitrogen bases (thymine/uracil)

Question 4

Which direction is new DNA built in?

Answer 4

5’ to 3’

Question 5

What enzyme makes new DNA?

Answer 5

DNA polymerase III

Question 6

When building new DNA, enzymes require a template strand and a starting point, called a _____.

Answer 6

Primer

Question 7

What enzyme breaks the hydrogen bonds between bases and separates the DNA strands?

Answer 7

Helicase

Question 8

What is the name of the molecule that prevents DNA from rewinding during replication?

Answer 8

Single-stranded binding proteins.

Question 9

What are primers? What makes them? Where are they added?

Answer 9

Primers are short strands of RNA. Made with primate. Added to single strand at the 5’ end.

Question 10

DNA can only be added in the ________ direction, but the newly formed lagging strand runs __________.

Answer 10

5’ to 3’, 3’ to 5’.

Question 11

What is the name of the fragment type that DNA polymerase III uses to build up new DNA?

Answer 11

Okazaki Fragments

Question 12

What enzyme joins together Okazaki fragments?

Answer 12

DNA ligase

Question 13

Short, single stranded ends of DNA are called ______. As these shorten, the cell ages and dies.

Answer 13

Telomers.

Question 14

What enzyme ‘checks’ for errors in DNA replication, and how?

Answer 14

DNA polymerase I, catches errors in base pairing by recognizing absence of hydrogen bonds

Question 15

Describe transcription, in simple terms.

Answer 15

DNA is organized into segments called genes. RNA polymerase sees the TATAA box (promoter sequence) and copies DNA into mRNA.

Question 16

Why can errors occur in transcription?

Answer 16

No proofreading (DNA polymerase I)

Question 17

How does transcription end?

Answer 17

RNA polymerase reaches the terminator sequence (G’s, C’s, A’s). Pre-mRNA detaches.

Question 18

pre-mRNA is processed in 3 steps before it leaves the nucleus. Name these steps.

Answer 18

1 - 5’ cap added.
2 - poly-A tail added
3 - spliceosomes remove introns (no coding sequences) and reconnect exons (coding sequences)

Question 19

What two things are needed for TRANSLATION?

Answer 19

tRNA and ribosomes

Question 20

What is an anticodon?

Answer 20

3 nucleotides that are complementary to the mRNA codon. Allows tRNA to stick to mRNA codon.

Question 21

Ribosomes have three binding sites for tRNA. Name them and what they do.

Answer 21

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.

Question 22

Describe the initiation of translation.

Answer 22

mRNA reaches the cytoplasm and sticks to rRNA in the ribosome. Anticodon (complementary to start codon AUG) bonds to mRNA in the P-site

Question 23

Describe the elongation process of translation in 3 steps.

Answer 23

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.

Question 24

Describe the termination process of translation

Answer 24

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.

Question 25

Name three methods of gene regulation in eukaryotes, and explain each

Answer 25

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)

Question 26

How is gene expression regulated in prokaryotes?

Answer 26

Protein production is controlled ONLY by transcriptional regulation (on or off)

Question 27

What is an operon?

Answer 27

Blocks of proteins that have been encoded together, as they are all needed for the same function or biochemical pathway.

Question 28

Name the three regions of the operon and what they do.

Answer 28

1 - coding region (contains codons)
2 - promoter site (TATAA box - RNA polymerase binds)
3 - operator (DNA region that determines if transcription happens)

Question 29

What is Lac Operon?

Answer 29

An operon that codes for LACTASE in bacteria like E. Coli. Breaks lactose into glucose and galactose for usable energy.

Question 30

What two conditions must be met for lac operon to be activated?

Answer 30

low/absent glucose levels, and lots of lactose.

Question 31

How does the lac operon function? Give both scenarios.

Answer 31

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.

Question 32

How do restriction enzymes work?

Answer 32

Cut DNA like molecular scissors at certain sequences (restriction site). Leaves ‘sticky ends’ of the DNA.

Question 33

Describe how DNA is amplified using bacterial vectors.

Answer 33

Restriction enzymes cut open bacterial DNA (plasmid). Same striction enzyme cuts out DNA sequence of interest. Sequence inserted into plasmid, sticky ends base pair.

Question 34

What does PCR stand for?

Answer 34

Polymerase Chain Reaction

Question 35

Describe how PCR amplifies DNA

Answer 35

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.

Question 36

Describe how gel electrophoresis can be used to analyze DNA.

Answer 36

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).

Question 37

Name the three types of point mutations. Give examples, using the start code UGC (cysteine).

Answer 37

Nonsense mutation: UGA (stop)
Missense mutation: UGG (tryptophan)
Silent mutation: UGU (cysteine)

Question 38

What are the two types of missense gene mutations? What does it mean?

Answer 38

Conservative (basic protein) and non-conservative (polar protein)

Question 39

What are the two types of base substitution mutations?

Answer 39

Transition (one purines for another) and trans version (purines for a pyrimidine)

Question 40

What is a frameshift mutation? What are the types?

Answer 40

A mutation that changes the reading frame of a nucleotide sequence. DNA can be INSERTED or DELETED (Insertion/deletion mutations)

Question 41

Name the four types of chromosome mutations.

Answer 41

Deletion, duplication, insertion, translocation.

Question 42

Why are chromosome mutations more serious than gene mutations?

Answer 42

Chromosomal mutations affect whole sets of genes, altering more genetic information and often having more serious effects.