BIOLOGY: Molecular Genetics Test

Question 1

What is DNA composed of, look like, and located?

Answer 1

• Deoxyribose sugar
• Adenine and Thymine, Cytosine and Guanine,
• Double stranded helix
• Located in the nucleus

Question 2

What is RNA composed of, look like, and located?

Answer 2

• Ribose sugar
• Adenine and Uracil, Cytosine and Guanine
• Single stranded
• Located in the nucleus and cytosol

Question 3

What makes up a nucleotide?

Answer 3

Sugar, phosphate group, and nitrogenous base

Question 4

Where are glycosyl bonds located?

Answer 4

The nitrogenous bases and sugar

Question 5

Where are phosphodiester linkages located?

Answer 5

A phosphate group of one nucleotide with the next nucleotide

Question 6

Upstream

Answer 6

A region (base sequences) of DNA located adjacent to the start of a gene

Question 7

Promoter

Answer 7

Upstream sequence of DNA where RNA polymerase binds. Indicates which DNA strand should be transcribed and where transcription begins. Promoter region is usually high in Adenine and Thymine. It is easy for RNA polymerase to begin there because it takes less energy to unwind DNA when there are only 2 hydrogen bonds.

Question 8

Template strand

Answer 8

The strand of DNA that RNA polymerase uses as a guide to make a complementary mRNA

Question 9

Coding strand

Answer 9

The strand of DNA not used for transcription; is identical to mRNA except mRNA contains U and not T

Question 10

RNA polymerase

Answer 10

Enzyme that binds to DNA, unwinds and builds the single stranded RNA molecule.

Question 11

Terminator sequence

Answer 11

Sequence of bases at the end of a gene that signals RNA polymerase to stop transcribing

Question 12

Primary Transcript

Answer 12

Newly made mRNA that has not departed the nucleus and needs to be modified still

Question 13

5’ Cap

Answer 13

Added to start of primary transcript. Consists of 7 methyl guanosine. Protects mRNA from digestion by nucleases and phosphates when it exits nucleus

Question 14

Poly-A tail

Answer 14

String of 200 adenine ribonucleotides added to 3’ end of transcript by enzyme poly-A polymerase. Protects mRNA from degradation and attacks by RNA digesting enzymes in the cytosol.

Question 15

Poly- A polymerase

Answer 15

Enzyme that adds adenine nucleotides to create the Poly-A tail

Question 16

Introns

Answer 16

Non coding regions of a gene that must be removed from transcript

Question 17

Exons

Answer 17

Coding regions; code for part of a specific protein

Question 18

Spliceosomes

Answer 18

Remove introns from mRA and join remaining exon regions

Question 19

mRNA transcript

Answer 19

Varies in length, depending on the gene that has been copied. It acts as the intermediary between DNA and the ribosomes. It is translated into proteins by ribosomes and is the RNA version of the gene encoded by DNA

Question 20

Describe transcription initiation

Answer 20

Transcription begins when RNA polymerase binds to the DNA and unwinds starting at the promoter. More specifically, RNA polymerase binds to the TATA box because it has a high percentage of adenine and thymine, which only have 2 hydrogen bonds that are easy to break. The purpose of this stage is to begin unwinding the DNA, starting at the TATA box in the promoter region, where it is easiest to split apart.

Question 21

Describe transcription elongation

Answer 21

RNA polymerase continues transcribing as it begins to build the single strand RNA molecule without a primer. RNA is made in the 5’ to 3’ direction using the 3’ to 5’ strand called the template strand. The opposite DNA strand is referred to as the coding strand, as it contains the exact same sequence as the RNA molecule. While RNA polymerase is transcribing, another RNA polymerase may start transcription again at the promoter.

Question 22

Describe transcription termination

Answer 22

Transcription of a gene is terminated when the RNA polymerase recognizes a termination sequence. RNA transcript is released and RNA polymerase is free to bind to another promoter region. The termination sequence is a string of adenines, which is transcribed into uracil; nuclear proteins bind to poly uracil sit and stop transcription.

Question 23

Describe the post-transcriptional modifications

Answer 23

The transcribed RNA is a precursor to mRNA and is vulnerable to conditions outside of the cell nucleus. It must be modified by a Poly-A tail, a 5’ Cap and splicing. First, Poly-A polymerase adds a chain of 50-250 adenines to the 3’ end of the pre-mRNA, which allows for it to be translated efficiently and protects it from attacks of enzymes in the cytosol. Secondly, the 5’ Cap, a sequence of 7 guanines, are added to the start of the pre-mRNA which functions as the initial attachment site that the ribosome recognizes and will use. Finally, an enzyme-protein complex called a spliceosome excises introns (a non-coding sequence of DNA/RNA) and splices the exons (sequence of DNA/RNA that codes for a gene) together.

Question 24

Ribosomes

Answer 24

Made up of 2 units: small and large subunits. They are made from a combination of rRNA and ribosomal proteins. The small subunit has a binding site where the mRNA attaches. The large subunit has three binding sites: A, P, & E

Question 25

Reading Frame

Answer 25

A particular system for separating a base pair sequence into readable codons

Question 26

Anti-codon

Answer 26

A 3-nucleotide segment that is complementary to a codon on the mRNA

Question 27

Transfer RNA (tRNA)

Answer 27

Small RNA’s approximately 70-90 nucleotides long (mRNA is 100s long). They have regions that base pair with themselves creating double-helical segments. At the end of one segment is an anticodon: a 3-nucleotide segment that is complementary to a codon on the mRNA. The other end of the tRNA is the region that carries the amino acid that corresponds to the anticodon

Question 28

Aminoacyl-tRNA

Answer 28

The complex of the tRNA and the amino acid that binds to it.

Question 29

A (acceptor) site

Answer 29

Where the tRNA carrying its amino acid binds to the mRNA (Aminoacyl cite)

Question 30

P (peptide) site

Answer 30

Where the tRNA adds its amino acid to the polypeptide chain (Peptidyl site)

Question 31

E (exit) site

Answer 31

Where the tRNA exits the ribosome

Question 32

Release Factor

Answer 32

When the A site of the ribosome arrives at the stop codon on the mRNA, a protein release factor (RF) binds to this site instead of tRNA. This causes the polypeptide to be released from the P site and it is detached from the ribosome. The ribosomal subunits separate and detach from the mRNA.

Question 33

Describe translation initiation

Answer 33

Small and large ribosomal subunits associate with an mRNA molecule at the 5’ cap and an initiator tRNA. The first tRNA for initiation has the anticodon UAC that binds to the AUG (Methionine) start codon on mRNA
Step 1: Initiator Met-tRNA forms a complex with the small ribosomal subunit
Step 2: The complex binds to the mRNA 5’ cap. It will move along the mRNA until it reaches the AUG start codon
Step 3: The start codon is recognized by the anticodon of the Met-tRNA and the large ribosomal subunit binds to complete the ribosome at the P-site.
The ribosome will now read the mRNA nucleotide bases 3 at a time (i.e. codons). To ensure the bases are read correctly (to make the correct protein), a reading frame (a particular system for separating a base pair sequence into
readable codons) is established at the tRNA-AUG pairing location on the mRNA.

Question 34

Describe translation elongation

Answer 34

Step 1: Elongation begins when the initiator tRNA is bound to the P site, the A site is empty
Step 2: The second tRNA with the appropriate anticodon and amino acid binds to the mRNA codon in the A site of the ribosome The 1st amino acid (Met) is cleaved from the tRNA in the P site and forms a peptide bond with the amino acid on the tRNA in the A site The new polypeptide chain is attached to the tRNA in the A site and the empty tRNA is in the P site
Step 3: The ribosome moves to the next codon on mRNA. tRNA in the A site moves to the P site, tRNA in the P site moves to the E site. The A site becomes open again to accept the next amino acid attached to its tRNA

Question 35

Describe translation termination

Answer 35

There is no tRNA for the stop codons (UAA, UAG, UGA). When the A site of the ribosome arrives at the stop codon on the mRNA, a protein release factor (RF) binds to this site instead of tRNA.
This causes the polypeptide to be released from the P site and it is detached from the ribosome. The ribosomal subunits separate and detach from the mRNA.
The polypeptide becomes a functional protein once it goes through some processing and forms its 3D shape. Some proteins are composed of two or more polypeptide chains (e.g., hemoglobin). These polypeptides are produced via separate translation events and come together to form a single functioning protein.

Question 36

Operon

Answer 36

Cluster of genes that control a single promoter and coordinate gene expression.

Question 37

Operator

Answer 37

Sequence of bases that regulatory factors will bind to in order to control transcription

Question 38

Repressor proteins

Answer 38

Binds to the operator to repress (stop) transcription

Question 39

Inducer

Answer 39

The lac operon is known as an inducible operon because the inducer (signal molecule e.g., lactose) inactivates the repressor and allows the gene to be transcribed and translated to produce a protein.

Question 40

Corepressor

Answer 40

Tryptophan acts as a signal molecule and activates the repressor protein – in this situation, tryptophan is called a corepressor.

Question 41

Describe the lac operon… what kind of gene expression is it?

Answer 41

• Enzyme Induction
  The lac operon is a cluster of genes that contain the DNA sequences to regulate the protein needed for the metabolism of lactose. When no lactose is present, the production of those proteins is blocked in order to conserve energy. Lac operon consists of:
  Promotor: site where DNA transcription occurs
  Operator: sequence of bases that regulatory factors will bind to in order to control transcription
  Coding regions for the proteins/enzymes that need to be expressed
  Repressor protein: binds to the operator to repress (i.e. stop) transcription
  If lactose is NOT present in the cell:
  lacI protein binds to the operator, covering part of the promoter.
  RNA Polymerase cannot bind to the promoter
  Transcription is blocked. Therefore, no mRNA made, no translation occurs = no enzymes made.
  If lactose IS present:
  Lactose binds to lacI protein, changing its shape (induced-fit)
  lacI can no longer bind to the operator
  Transcription and translation proceed and the lactose metabolism enzymes are made.
  The lac operon is known as an inducible operon because the inducer (signal molecule e.g., lactose) inactivates the repressor and allows the gene to be transcribed and translated to produce a protein.

Question 42

Describe the trp operon… what kind of gene expression is it?

Answer 42

Enzyme Repression
The trp operon is an example of enzyme repression: the operon is repressed (turned off) when high levels of tryptophan are present. Therefore no tryptophan will be produced. The trp operon consists of:
Promoter Region
Operator Region
Five genes - code for five polypeptides that make three enzymes needed to synthesize the amino acid tryptophan.
If tryptophan is NOT present
Repressor protein is inactive and does not bind to the operator.
RNA polymerase binds to the promoter region and transcription occurs.
Tryptophan is produced.
If tryptophan IS present
Tryptophan acts as a signal molecule and activates the repressor protein – in this situation, tryptophan is called a corepressor.
Tryptophan will bind to the trp repressor, which activates it. The active trp repressor will bind to the operator and stop transcription.
No tryptophan is produced.

Question 43

What are the 4 types of point mutations?

Answer 43

Substitution, inversion, deletion, and insertion

Question 44

Define the substitution mutation and what are the results

Answer 44

The replacement of one base with another; results in either missense, nonsense or silent mutations.

Question 45

Define the insertion mutation and what are the results

Answer 45

The addition of an extra base pair in a DNA sequence; results in a frameshift mutation

Question 46

Define deletion mutations and what are the results

Answer 46

The elimination of a base pair or group of base pairs from DNA sequence; results in a frameshift mutation

Question 47

Define inversion mutations and what are the results

Answer 47

The reversal of two adjoining base pairs in a DNA sequence; results in a missense mutation

Question 48

Missense mutation

Answer 48

One amino acid is exchanged for another.

Question 49

Nonsense mutation

Answer 49

A codon for an amino acid is replaced by a stop codon.

Question 50

Silent mutations

Answer 50

A mutation that does not change the amino acid coded for, and therefore there is no phenotypic change

Question 51

Frameshift mutations

Answer 51

Mutation that causes the reading frame of codons to change. Results in different amino acids being incorporated into polypeptide

Question 52

What are the 2 chromosomal mutations and what is the result?

Answer 52

• Translocation: entire genes or sequences move from one chromosome to another; portions of chromosomes break off and exchange places resulting in an entirely new gene.
• Inversion: the reversal of a large number of base pairs in a DNA sequence; depending where this happens in the coding sequence, the gene may be compromised.
• Result: Entire coding regions may be removed or inverted. A large loss of genetic material may negatively affect the functioning of the cell.

Question 53

What are the causes of mutations?

Answer 53

Spontaneous mutations and induced mutations

Question 54

Explain spontaneous causes of mutations

Answer 54

Mutation is caused by an error during DNA replication. (E.g., DNA polymerase “misses” errors in duplicated DNA = Point Mutation)

Question 55

Explain induced causes of mutations

Answer 55

Mutation is caused by the effect of an environmental agent (mutagen) (E.g., chemical, UVB radiation, X-rays)
- Chemical mutagens: A particular chemical agent enter the nucleus and chemically alters the structure of DNA ∙ E.g., carbon monoxide found in vehicle exhaust and tobacco smoke
- Electromagnetic Radiation: Lower energy radiation (e.g., UVB) can cause bonds to form between adjacent nucleotides creating a kink in the DNA backbone, which complicates replication and transcription ∙ Higher energy radiation (e.g., X-rays) can strip molecules of electrons and break bonds within the DNA molecule, which may result in a deletion or rearrangement of large portions of chromosomes

Question 56

How do mutations affect different age groups?

Answer 56

Mutations would affect younger age groups more crucially and negatively, as the cells and bodies are rapidly growing. Throughout the growth, if a mutation was present, they are more perceptible to development delays and structural abnormalities. However, adults and elderly are less affected by mutations in development genes, since they are not growing much. The mutation in older people may cause diseases such as cancer.

Question 57

What is a telomere?

Answer 57

Telomeres are retreating sequences of DNA that are found on the ends of chromosomes. They prevent the loss of coding regions of DNA during replication.

Question 58

What is telomerase?

Answer 58

An enzyme that adds new telomere sequences to the ends of chromosomes, restoring their length

Question 59

What is the relationship between telomeres and aging?

Answer 59

Telomeres do not control aging but plays a role in how our bodies change as we get older. Because not all cells reproduce at the same rate, cells will not undergo senescence at the same time, and function less than optimally. The loss of telomeres after many replication events causes the loss of function which is the cause of dysfunction in elderly people.

Question 60

What are the benefits of medical therapies that influence telomerase?

Answer 60

Some new medical therapies inhibit the production of telomerase which is important for diseases like cancer. Cancer cells are dangerous because they never stop dividing and produce telomerase in great quantities. If medical therapies represses the production of telomerase, they can reduce the spread of cancerous cells. Aswell, if medical therapies found a way to induce telomerase production on our healthy cells, it would increase the longevity and prevent aging/function loss of the cell.