Molecular Genetics

Question 1

Explain why researchers originally thought protein was the genetic material.

Answer 1

Biochemists knew that genetic material had to be diverse and have a multitude of functions. At the time when genetics was first being researched, very little was known about nucleic acids. They seemed too uniform to be capable of producing the many inherited traits exhibited by every organism. Researchers then looked at protein, which they classified as a macro-molecule (has many atoms), and figured that it had to be the genetic material, due to the fact that it was incredibly diverse and had a multitude of functions, and would be able to produce a wide variety of traits.

Question 2

Frederik Griffith

Experiment and Discovery.

Answer 2

Discovered the concept of transformation, where an organism can be genetically and phenotypically changed by external DNA.
Worked with two strains of bacteria, one pathogenic (produced rough edges) which caused pneumonia and one non-pathogenic (produced smooth edges). He injected a mouse with a mixture of heat-killed bacteria, and non-pathogenic and found that the mouse died. This proved that it was something in the bacteria’s DNA which caused it to be harmful, not a toxin inside the cell.

Question 3

Oswald Avery, McCarthy, MacLeod

Experiment and DIscovery

Answer 3

Found that DNA was the transforming agent, not protein

Exposed S cells to the protein and DNA of R cells and found that DNA caused the change.

Question 4

Hershey and Chase

Experiment and Discovery

Answer 4

Worked with phages, which are viruses that only infect bacteria
Phages have a protein coating on the outside, and DNA on the inside. They grew two cultures of E.coli cells with a phage called T2, and tagged the protein with a radioactive isotope of sulfur, and the DNA with radioactive phosphate. When they stripped the phages from the outside of the bacteria, they found that the interior was tagged with phosphorus, i.e DNA.

Question 5

Chargaff

Answer 5

#Adenine=Thymine
#Cytosine=Guanine
DNA composition varies from one species to another, proving that DNA is molecularity diverse.

Question 6

Viral genomes can consist of…(types of DNA)

Answer 6

Single/double stranded D/RNA

Question 7

Capsid

Answer 7

The protein shell enclosing a viral genome.
Can be rod shaped-polyhedral, or more complex
Made of protein subunits called capsomeres

Question 8

Viral Structure

Answer 8

nucleic acid in a protein coat and occasionally a membranous envelope

Question 9

Why can’t a virus make a protein?

Answer 9

It lacks metabolic enzymes, ribosomes, and other equipment needed for making proteins.

Question 10

How to viruses identify their host cell?

Answer 10

Lock and key fit between proteins on the outside of the virus and specific receptor molecules on the surface of the cells.

Question 11

Capsomeres

Answer 11

Protein shell enclosing a viral genome, made of protein subunits called capsomeres

Question 12

How do viruses reproduce?

Answer 12

Once the host cell is infected, the virus then uses the material inside the host cell to reproduce (i.e DNA polymerase, ribosomes, amino acids, nucleic acids, etc.) The progeny of these infected cells have teh capability to infect other cells.

Question 13

The Lytic Cycle

Answer 13

Page reproductive cycle, which ends in the death of the host cell. It is the last stage of infection, in which the bacterium breaks open (lyses) and releases the phages that were produced within the cell, they can now infect healthy cells.

Question 14

Virulent phage

Answer 14

Virus which only produces by a lytic cycle

Question 15

Restrictions enzymes

Answer 15

Recognize foreign DNA from phages and cut it up before it can cause any damage

Question 16

Lysogenic cycle

Answer 16

Allows phage genome to be repplicated without destroying the host

Question 17

Temperate phages

Answer 17

Phages capable of both the lysogenic and lytic cycle for reproduction.

Question 18

Stages of The Lytic Cycle

Answer 18

Attachment: phage uses its tail fibers to bind to specific receptor cites on the outer surface
Entry: The sheath of the tail contracts, injecting phage DNA into the cell and leaving an empty capsid outside. The cell’s DNA is hydrolyzed
Synthesis of viral genomes and proteins: Phage DNA directs production of phage proteins and copies phage genome by host enzymes
Assembly: Proteins form phage head, tail, and tail fibers
Release: Phage directs production of an enzyme which damages the cell wall allowing fluid to enter, the bacterial cell bursts and the phages are released

Question 19

Prophage

Answer 19

Virus is integrated into the DNA via crossing over
Every time the cell prepares to divide, it replicates the phage DNA along with its own and passes the copies on to the daughter cells.

Question 20

Structure of a Viral Envelope

Answer 20

Viral glycoproteins extend outward, which contains either DNA or RNA.

Question 21

Retrovirus

Answer 21

Have the most complicated reproductive cycles. Have an enzyme called reverse transcriptase which transcribes RNA template into DNA changing the direction of informational flow.

Question 22

Provirus

Answer 22

integrated viral DNA which never leaves the cell

Question 23

Viroids

Answer 23

Circular RNA molecules which are short. They do not encode proteins, but can replicate in host plant cells.

Question 24

Prions

Answer 24

Infectious proteins.
It is a misfolded form of a protein which upon entering the cell containing the normal form, converts the normal protein into the prion version.

Question 25

Nucleoid

Answer 25

Super coiled DNA found in bacterial cells, since stretched out DNA would be 500x larger than the cell

Question 26

Conjugation

Answer 26

Bacterial sex. Transfer of DNA from one bacteria to another via a cytoplasmic junction called a mating bridge, inside the sex pilus.

Question 27

F Factor

Answer 27

gene needed for a sex pilus to be created

Question 28

Transposable elements

Answer 28

genetic information that exists sole within the chromosomal or plasmid DNA.

Question 29

Transposition

Answer 29

Movement of transposable elements

leads to genetic diversity by moving genes to places where they have not been seen before.

Question 30

Insertion sequences

Answer 30

Complex transposeable elements which only exist in bacteria.Single gene with codes for transposable, an enzyme which catalyzes movement of insertion sequence from one site to another within the genome.

Question 31

Transposons

Answer 31

Complex transposable elements, more complex than insertion sequences.
Include extra genes
Help bacteria adapt to new enviornments

Question 32

Transcription: definition, and what it does

Answer 32

RNA is synthesized by DNA, DNA template strand is scanned by RNA polymerase and creates mRNA in the 5’ to 3’ direction

Question 33

Operon

Answer 33

A group of tightly linked genes that act together and code for enzymes that control a particular metabolic pathway

Question 34

Parts of an Operon

Answer 34

Repressor
Promoter
Operator
Structural Gene
Regulator Gene

Question 35

Describe the structure and function of telomeres.

Answer 35

Telomeres are located at the ends of DNA molecules ,they are nucleotide sequences which do not contain genes. They consist of multiple repetitions of one short nucleotide sequence. These repetitions can occur anywhere from 100 to 1,000 times. These telomeres protect the genes from being eroded through replication. It also prevents the staggered ends of the daughter molecule from activating the cell’s systems for monitoring DNA damage. They do not prevent the shortening of DNA molecules, the just postpone the erosion of genes near the ends of the DNA molecules. They become shorter after every round of replication. The telomeric DNA is shorter in dividing somatic cells of older individuals.

Question 36

Distinguish between the leading strand and the lagging strand.

Answer 36

The leading strand is one that is created by DNA polymerase as it moves in the mandatory 5’ to 3’ end. It starts at the replication fork, and works its way towards the 3’ end. This strand is complementary to the template strand. The DNA strand synthesized before the replication fork, it is synthesized in a series of segments.

Question 37

Describe the structure of DNA. Explain the base-pairing rule and describe its significance.

Answer 37

DNA consists of a sugar phosphate backbone which gives it its stability, with the nitrogenous bases, adenine, thymine, guanine, and cytosine on the inside and are held together by hydrogen bonds. Watson and Crick’s calculation of the width of DNA allowed them to be able to determine which bases paired together, and through trial and error, discovered that a purine, a double ringed structure, had to pair with a pyrimidine, a single ringed structure, in order for the width to be what it was. They then confirmed that adenine (purine) pairs with thymine (pyrimidine), and guanine (purine) pairs with cytosine (pyrimidine)

Question 38

Explain the general process of transcription, including the three major steps of initiation, elongation, and termination.

Answer 38

Transcription is where the DNA molecule (transcription unit) is copied by RNA. RNA polymerase separates the two strands of DNA and starts attaching the RNA nucleotides to the base pair along the DNA template. This enzyme can only move in the 5’->3’ direction. It is, unlike DNA polymerase, able to start a chain from scratch, there is no primer needed.
In Initiation, RNA polymerase binds to the promoter, the starting point of transcription, indicated by a specific sequences of bases. Once RNA polymerase binds to the promoter, RNA synthesis starts.The enzyme moves down the DNA strand, unwinding it as it goes, and it elongates the RNA transcript in the 5’ to 3’ direction in a process called Elongation. After the DNA is transcribed, it goes back to its double helix model. when the RNA transcript is released, and the polymerase detaches from the DNA, this is called termination.

Question 39

Explain how RNA is modified after transcription in eukaryotic cells.

Answer 39

In eukaryotic cells, DNA doesn’t go straight to mRNA. It has an intermediate called pre-mRNA. This is because of the eukaryotic cell’s nucleus, which separates transcription and translation. Before it can leave the nucleus, eukaryotic RNA transcripts are modified to produce the final functional mRNA. The pre-mRNA then becomes mRNA through RNA processing. During this process, the ends of the RNA transcript are usually altered, and in most cases, so are certain interior sections of the molecule. At the 3’ end of the molecule, an enzyme adds 50 to 250 adenine nucleotides, and forms what is called a poly-A tail. This tail helps to facilitate the export of the mature mRNA from the nucleus, and protect the mRNA from degradation, it also aids in attaching the ribosomes to the 5’ end of mRNA.

Question 40

Define and explain the role of ribozyme.

Answer 40

Ribozymes are RNA molecules which function as an enzyme. They are responsible for joining amino acids together for forming protein chains.

Question 41

Describe the functional and evolutionary significance of introns.

Answer 41

Introns are non-coding segments of a nucleic acids (also called intervening sequences). They contain a signal for RNA splicing at their ends, which signal for small nuclear ribonucleoproteins (snRNPs), which are located in the cell’s nucleus and are made of RNA and protein molecules, to create a spliceosome and release the intron and join two exons together.