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Gr 12 Bio Exam > Molecular Genetics > Flashcards

Molecular Genetics Flashcards

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1
Q

Who is Gregor Mendel?

A

-“father of genetics”
- Dominant and recessive traits

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2
Q

What did Fredrick Meischer do?

A
  • Discovered the nucleic acids
  • Discovered the nucleus contains acidic and alkaline portions. (DNA and RNA)
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3
Q

What was Fredick Griffith known for

A
  • mouse and s.pneumonia experiement
  • discovered the “transforming principle”
  • Obtained evidence of how DNA plays a role in heredity
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4
Q

What is Chargaff’s rule?

A
  • That the nucleotides which make up nucleic acids are always found in equal compositions of Adenine and Thymine, Guanine and Cytosine

A=T

G=C

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5
Q

Describe the components of a nucleotide

A

A 5-carbon sugar attached to an inorganic phosphate and a nitrogenous base

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6
Q

What are the different nitrogenous bases found in nucleotides?

A

In DNA:
- Adenine + Thymine
- Guanine + Cytosine

In RNA
- Adenine + Uracil
- Guanine + Cytosine

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7
Q

Describe the experiment lead by Fredrick Meischer

A

The s.pneumonia, mice experiment was one in which mice were injected with two different forms of pneumonia, one which is pathogenic and the other which isn’t. A set of mice were injected with both forms of pneumonia both live and heat-killed. With this experiment, Meischer concluded the transforming principle in which a dead cell’s pathogenic properties may be passed on to living bacterial cells.

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8
Q

Describe the double helix structure of a DNA molecule

A
  • 5 carbon sugars attached to phosphate group make up the sugar phosphate backbone of nucelotides
  • Nucleotides are conjoined at the center by hydrogen bonds
  • Each strand of a DNA molecule are oriented in opposite directions
  • Genes on the strands are read in the 5-3 direction
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9
Q

What factors maintain the stability of a DNA double helix structure

A
  • hydrogen bonds between the nucleotides hold each pair together
  • The sugar-phosphate handrails are linked by phosphate bridges
  • hydrophobic components are suspended on the inside while hydrophilic components are exposed to the outside
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10
Q

What are the key differences between ribonucleic acids and deoxyribonucleic acids?

A

1) RNA is single-stranded
2) RNA contains uracil instead of thymine
3)RNA does not contain the sugar deoxyribose but instead ribose

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11
Q

How is genetic material contained in prokaryotes?

A

The genetic material in prokaryotes is contained in the cell’s nucleoid, a region that isn’t enclosed by a double membrane.

The genetic material is compacted in the nucleoid through supercoiling and binding together to form a belt.

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12
Q

What are plasmids?

A

Plasmids are additional pieces of DNA found in the form of small circular double-stranded DNA molecules which float freely in the cytoplasm.

These additional pieces of DNA may be copied and transmitted between cells.

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13
Q

What is the arrangement of DNA in Eukaryotes?

A

DNA in eukaryotes is contained in the cell’s nucleus, a membrane enclose structure.

DNA is compact within the nucleus as chromosomes as Eukaryotes contain much more DNA than prokaryotes.

Each chromosome consists of one double-stranded DNA molecule tightly wrapped around histone proteins which string together in a series of nucleosomes. The nucleosomes pack together to form chromatin fibres

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14
Q

Describe Watson and Crick’s 3 different theories of DNA replication

A

Conservative theory - After replication, the parent DNA strands would reform and the two replicated daughter strands would form new DNA molecules

Semi-conservative theory - After replication a parent strand would match up with a daughter strand

Dispersive theory - the parent strands would break into small fragments in which each new DNA molecule consisted of both small fragments of the replicated daughter strand and the parent strands

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15
Q

What was Franklin and Stahls discovery? (experiment + result)

A

Franklin and Stahl resolved the three major theories of DNA replication by performing an experiment in which bacteria was grown in the presence of radioactive nitrogen allowing the bacteria to incorporate its presence into its DNA. Next, the same colony was transferred to a different medium containing regulated nitrogen. After further growth of the colony, the bacteria’s DNA was observed resulting in a hybrid of both the radioactive nitrogen and the regular nitrogen at similar densities ruling out conservative theory. The experiment was repeated and the conclusion came to the idea that DNA replication follows the semi-conservative theory.

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16
Q

What are the three major steps of DNA replication?

A

1) Initiation
2) Elongation
3) Termination

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17
Q

Describe each of the Initiation steps of DNA replication

A

Prokaryotes and Eukaryotes: The enzyme helicase attaches to the replication origin of a strand of DNA and separates the two strands.

A replication bubble is opened in which DNA polymerase is attached to the replication origin. The DNA polymerase moves along the opened parent strand in the 5-3 direction adding complementary nucleotides forming the daughter strand.

Each end of the replication bubbles by which the DNA polymerase is moving along is called the replication fork. The replication forks continue to open as helicase which cleaves and reveals the double-stranded DNA continues to move along the strands.

Replication on a singular strand may take place at multiple replication origins at a time.

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18
Q

Describe the elongation step of DNA replication on the Leading strand

A

For DNA polymerase to initally attach to the parent strand within the bubble, a primer (short strand of RNA) must be present at the replication origin (starting point)

Primer is attached to the parent strand by an enzyme called primase

The DNA polymerase attached to a parent strand of DNA within the bubble begins to add complementary nucleotides in the 5 - 3 direction creating a daughter strand.

Replication takes place in the direction of the forks opening

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19
Q

Describe DNA replication on the lagging strand

A

For the replication of both DNA strands to take place simultaneously, replication will take place in opposite directions.

The lagging strand will be replicated in the 3-5 direction.

Since DNA polymerase may only replicate molecules in the 5-3 direction, replication on the lagging strand is split into Okazaki fragments.

Each fragment is replicated in the 5-3 direction guided by the presence of primers in between each fragment attached by DNA primase.

As the DNA polymerase continues along the lagging strand working from 3-5, it adds complementary nucleotides and removes the initial primase.

DNA ligase binds the fragments together closing the space from the removed primers in between each new fragment.

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20
Q

Describe the termination process of DNA replication

A

Eukaryotes: During the termination process, The first primer attached to the 5 end at the start of replication is removed leaving no complementary nucleotide chain on the 3 end. This results in the start of the chain being left unpaired and for it to eventually break off.

As DNA is replicated and the new daughter strand is formed, the strands rewind naturally

Prokaryotes: In prokaryotes with circular DNA, the RNA primase does not cause unpaired ends

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21
Q

Name and describe the function of all the different enzymes and players used in the complete process of DNA replication in order

A

Helicase - Helicase cleaves to double-stranded DNA molecules and unwinds the two strands creating a replication bubble. A replication fork is the end where the helicase unwinds the double strands on each side of the replication bubble

Primase - attaches to the replication origin and attaches a short RNA molecule or primer in order to direct the DNA polymerase

DNA Polymerase - attaches to the replication origin and begins attaching complementary nucleotides to the replicated daughter strand

DNA Ligase - Binds the Ozaki fragments of the replicated daughter strand on the lagging strand through phosphate bonds and removes the spaces left by removed primer strands

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22
Q

What is a telomere?

A

Telomeres are the end regions of chromosomes which consist of a series of repeating nucleotide sequences which don’t contain any significant genetic code.

Telomeres undergo erosion as cells divide which is relative to cell death

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23
Q

How is replication proofread?

A

DNA polymerase can proofread and remove any errors in nucleotide sequences.

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24
Q

What is the main idea of the central dogma?

A

DNA –> RNA —> Proteins
- DNA never leaves the nucleus
- RNA is transcribed from DNA inside the nucleus
- RNA is used in the protein synthesis in the cytoplasm

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25
Q

Why doesn’t DNA ever leave the nucleus?

A

The movement of DNA back and forth from the cytosol to the nucleus expands a lot of energy and may cause potential damage to DNA molecules. Therefore transcription-producing mRNA is much more energy-efficient, safer for original DNA molecules and allows for the production of multiple RNA.

26
Q

What is are mRNA codons?

A

mRNA codons are a combination of 3 RNA bases which code for different amino acids depending on their code.

Certain combinations are known as start and stop codons which start and stop the transcription of polypeptides.

27
Q

What are the major steps of DNA to RNA transcription?

A
  • Initiation
  • Elongation
  • Termination
  • Processing
28
Q

What is the difference between the sense strand and the anti-sense strand?

A

The sense strand is the strand of DNA which is be transcribed, contains the instructions for mRNA

The anti-sense strand is the strain of the same DNA molecule which contains just the complementary bases to it’s double helix structure.

29
Q

What is a promoter sequence?

A

A sequence of code is recognized by RNA polymerase as the binding site for the synthesis of mRNA.

The promoter sequence ensures the RNA polymerase has attached to the correct strand, at the correct nucleotide sequence in the correct direction.

Promoter sequences are usually rich in T and A nucleotides and referred to as a TATA box

30
Q

Which strand is the promoter sequence found on?

A

The promoter sequence may be found on either strand, the sense or the anti-sense.

31
Q

Describe the initiation process of DNA transcription

A

The process begins with RNA polymerase attaching to the promoter sequence on either the sense or anti-sense strand of the DNA.

The RNA polymerase opens a small section of DNA and begins creating a new strand of nucleotides consisting of complementary nucleotides to those found on the template strand.

The DNA polymerase will only transcribe the DNA strand in the 5-3 direction opposite to the template strand

32
Q
A
33
Q

What functional group is found at the end of the 5 and 3 ends of DNA strands?

A

The 5 end consists of the phosphate group which attaches to the next nucleotide in the sequence

The 3 end consists of the OH (hydroxyl group)

34
Q

Describe the elongation process of DNA transcription

A

The elongation process consists of DNA polymerase opening up a section of the DNA, and working it’s way in the 5-3 direction starting at the hydroxyl group of the last nucleotide to add complementary bases of the template strand.

The DNA helix reforms as soon as the RNA polymerase has completed copying a certain section of the code.

The newly formed mRNA is then released from the DNA.

Also, as soon as RNA polymerase has completed one section from the promoter sequence, another RNA polymerase may attach to the same promoter sequence and begin another transcription.

35
Q

Describe the termination process of DNA transcription

A

Once the RNA polymerase meets a terminator sequence, transcription stops and the newly formed mRNA strand separates from the DNA template strand.

36
Q

Where does transcription take place in eukaryotes and prokaryotes?

A

Eukaryotes: In the nucleus
Prokaryotes: in the cell’s cytoplasm as for no nuclear membrane enclosing nucleic acids

37
Q

What processes does the final step of transcription consist of?

A

The final step of transcription consists of adding a 5 cap to the 5 end of the pre-mRNA and a poly-A tail to the 3 end. These two additions to the RNA protect it from enzymes which tend to break down nucleic acids within the cytosol and also function towards signalling to bind to molecules which synthesize polypeptides.

RNA splicing with the help of spliceosomes cut out any non-coding genes known as introns which were transcribed into the mRNA amongst a series of exons (significant nucleotide sequences)

After the processing step, in eukaryotes, the mRNA is transported outside of the nucleus to begin translation whereas in prokaryotes Translation may begin immediately after processing is complete

38
Q

What is transfer RNA?

A

Transfer RNA similar to mRNA are transcribed from genes on DNA template strands though tRNA molecules consist of regions which contain different complementary sequences resulting in their lobed shape.

Transfer RNA sequences are complementary to mRNA sequences.

Two main parts of tRNA structures include

1) The anti-codon sequence found at the end of a lobe which is complementary to the codon of an mRNA molecule

2) The amino acid attachment site which attaches the specific amino acids the the mRNA sequence codes for

39
Q

What are the two main parts of a tRNA molecule?

A

1) anticodon - complementary to mRNA
2) amino acid attachment site - to attach amino acids specified by mRNA

40
Q

What are activating enzymes?

A

Enzymes which catalyze the binding of an amino acid to the tRNA amino acid attachment site

41
Q

What are tRNA molecules which are bound to amino acids called?

A

aa-tRNA

42
Q

What role do ribosomes play in translation?

A

An active ribosome consists of 2 subunits a large and small ribosome is where the aa-tRNA, the mRNA and other needed components come together to perform protein synthesis

42
Q

Describe the different binding sites of an activated ribosome and what happens at each site

A

The large subunit sits ontop of the small subunit

The small subunit has a binding site for the mRNA to attach to which contains a rRNA (ribosomal RNA)

The large subunit consists of three binding sites

1) The P site (middle) is where the aa-tRNA is held along with a growing chain of amino acids

2) the A site (right side) is where the next aa-tRNA is held to attach the next amino acid to the chain

3) the E site (left side) is where the tRNA molecule is released

43
Q

Describe the 3 main steps of translation

A

1) initiation - small and large subunits come together, mRNA molecules are transported from the nucleus to the cytoplasm and attach to the binding site on the small subunit of an activated ribosome. tRNA which binds to their corresponding amino acids with the help of activation enzymes form aa-tRNA molecules that attach to the a site of the large ribosomal subunit. Leader sequences on the mRNA allow the ribosomal subunits to bind to the correct gene sequences.

2) Elongation - base pairs are formed between aa-tRNA and the mRNA. The aa-tRNA first attaches to the A site then moving 3 units in the 5-3 direction, the tRNA moves to the P site and allows another tRNA to attach to the A site on the large ribosomal subunit. The amino acid chain is held at the P site and new amino acids are bound to the chain from the A site. tRNA moves to each site through translocation, once at the E site, the tRNA is released

3) Termination - When a stop codon is found in the A site, the translation process is terminated. A releasing factor cleaves the newly formed polypeptide chain and releases it from the P site. The ribsome dissasembles and attaches to other mRNA sequences to be translated.

44
Q

How is translation different in prokaryotes?

A

In prokaryotes, translation may take place as soon as mRNA is transcribed as translation and transcription both take place in the same location considering that prokaryotes do not contain ay barrier between their nucleic acids from which mRNA is transcripted and ribosomal subunits from which the mRNA is translated.

45
Q
A
46
Q

What does gene regulation refer t?

A

The ability of a cell to adapt to different environmental changes and conditions through the control of its’ production of polypeptides

47
Q

When is it most optimal for gene regulation to take place in prokaryotes?

A

As prokaryotes carry transcription and translation simultaneously, transcriptional control is not very effective therefore the most effective stage in which gene regulation may take place during processes which affect transcription in prokaryotes.

48
Q

What is an operon?

A

An operon is a set of genes on a DNA molecule responsible for or involved in a metabolic pathway

49
Q

What is an operator and what does it do?

A

An operator is a regulatory sequence found within the promoter sequences which defines whether RNA polymerase may bind to the promoter sequence to begin transcription or not

50
Q

Describe negative gene regulation in the lac operon

A

negative gene regulation in the lac operon is when a repressor molecule binds to the operator of a gene sequence stopping RNA polymerase from attaching to the promoter sequence and transcribing DNA. This takes place when no lactose is available

When lactose is available, the lactose molecules will bind to the repressor causing it to detach from the operator and allow for transcription. In this case the lactose molecule is considered an inducer

51
Q

Describe positive gene regulation in the lac operon

A
52
Q

What is the difference between a repressor and an inducer?

A

A repressor molecule binds to the operator of a DNA sequence and makes transcription impossible

An inducer such as lactose molecules allows the repressor to detach from the operator and allow transcription once more

53
Q

What is a corepressor?

A

A molecule which increases the affinity of the repressor for the operator.

54
Q

What type of cell causes mutations to be inherited by further generations

A

Not somatic cells
Germ cells

55
Q

What is point mutation?

A

the insertion, substitution or deletion of one or more nucleotides

56
Q

What is a silent mutation?

A

A point mutation in which the mutation does not affect the cell’s metabolism

57
Q

What is a missense mutation?

A

A point mutation which produces a functional yet slightly altered product

58
Q

What is a non-sense mutation?

A

A point mutation in which the genes produce completely non-functional

59
Q

What are frameshift mutations?

A

A type of Point mutation in which the insertion or deletion of a nucleotide affects the entire sequence of codons

Gr 12 Bio Exam (9 decks)

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