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Biology MCAT > Genetic Code & DNA > Flashcards

Genetic Code & DNA Flashcards

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1
Q

What are the four nucleotides that make up the nucleic acids DNA and RNA?

A

DNA: Adenine, Cytosine, Guanine, and Thymine

RNA: Adenine, Cytosine, Guanine, and Uracil

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2
Q

What are the full names of DNA and RNA?

A

DNA- Deoxyribonucleic Acid

RNA - Ribonucleic Acid

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3
Q

What are the three parts that make up nucleotides?

A

Nitrogenous Base
Pentose Sugar (5 carbon sugar)
Phosphate Group

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4
Q

What is a nucleoside?

A

A nucleotide with no phosphate group.

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5
Q

What sugar does RNA use? What sugar does DNA use?

A

RNA- Ribose

DNA- Deoxyribose (No hydroxyl, -OH, group on the 2nd position carbon)

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6
Q

What charge does a phosphate group have?

A

A negative charge

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7
Q

What is cAMP?

A

It is Cyclic Adenosine Monophosphate and is a signaling molecule.

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8
Q

What kind of structures are nitrogenous bases?

A

Cyclic (rings)

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9
Q

What are the two different categories of nitrogenous bases?

A

Pyrimidines (have one ring) and purines (have two rings)

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10
Q

Which nitrogenous bases are pyrimidines?

A

Cytosine - has an amine group
Thymine - has methyl group
Uracil

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11
Q

Which nitrogenous bases are purines?

A

Adenine

Guanine - has a carbonyl group

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12
Q

How many hydrogen bonds do cytosine and guanine have?

A
  1. This makes G-C bonds have a higher melting temperature than A-T and A-U bonds.
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13
Q

How many hydrogen bonds do adenine and thymine have? adenine and uracil?

A

2

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14
Q

Do nitrogenous bases experience hydrophobic interactions?

A

Yes, they experience hydrophobic interactions with adjacent bases stacked on top of one another. This makes the nucleic acids more stable

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15
Q

What does Chargaff’s Rule state?

A 
A:T  = 1:1
C:G = 1:1
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16
Q

How are individual nucleotides joined together in a nucleic acid strand?

A

In a linear string by sugar-phosphate backbone. Alternating units of pentose sugars and phosphate groups are connected by phosphodiester linkages.

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17
Q

How exactly do phosphate groups link two nucleotides together?

A

By binding the 3’ carbon on the sugar of one nucleotide and also by binding the 5’ carbon on the sugar of the second nucleotide.

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18
Q

Which nucleic acid is usually a single strand?

A

RNA which makes it less stable than the double stranded DNA

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19
Q

Do viruses have single strand or double strand RNA?

A

Viruses can have single RNA and DNA strands or double RNA and DNA strands

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20
Q

How could we separate the double strands of a DNA molecule?

A

By using heat or chemical denaturants, like urea to denature (separate) the two strands. This is known as melting DNA

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21
Q

What is the melting temperature (Tm) for DNA?

A

Temperature where 50% of DNA strands have been denatured.

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22
Q

What is annealing?

A

Reverse denaturing. Two complementary DNA strands reassociate with each other

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23
Q

Is DNA usually right handed or left handed?

A

Right handed

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24
Q

What is B-DNA?

A

The most common form of DNA. It is about 10.5 base pairs per turn of the double helix. 10.5 base pairs = 34 Angstroms

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25
Q

What is A-DNA?

A

It is the dehydrated form of B-DNA. Can be formed by DNA-RNA hybrid helices. It has a tighter structure.

26
Q

What is Z-DNA?

A

It is left handed and the loosest/less condensed DNA

27
Q

What is the main function of DNA? Main function of RNA?

A

DNA - stores and transmits genetic information.

RNA - decodes DNA to make proteins

28
Q

What is the Central Dogma of Molecular Biology?

A

DNA is transcribed (transcription) into mRNA and mRNA is translated (translation) into proteins.

29
Q

Why is the Hershey-Chase experiment important?

A

It lead to first evidence that DNA is genetic material.

30
Q

Where is nuclear DNA found?

A

On 23 chromosome pairs.

31
Q

Where does transcription occur?

A

In the nucleus

32
Q

Where does translation occur?

A

In ribosomes

33
Q

What are the different types of RNA and what are their main functions?

A

Messenger RNA (mRNA) - template to synthesize protein

Heterogenous Nuclear RNA (hnRNA) - precursor to mRNA. It is spliced and modifies to mature mRNA

Transfer RNA (tRNA) - has clover leaf structure and transfers amino acids to growing polypeptide chain

Ribosomal RNA (rRNA) - made in the nucleolus and makes up more than 50% of ribosomes by weight. Acts as riboenzymes (RNA enzymes)

Small Interfering RNA (siRNA) - inhibit gene expression

Micro-RNA (miRNA) - inhibit gene expression

34
Q

What is the common role of all RNA?

A

It has various steps in gene expression, which impacts the production of proteins made from genetic sequences

35
Q

What does the enzyme reverse transcriptase do in viruses?

A

It is a type of DNA polymerase which reverse transcribes RNA back into DNA, which helps virus spread widely in its host.

36
Q

What do ribosomes do?

A

They decipher genetic code that is copied into the mRNA sequence

37
Q

What are codons?

A

3 nucleotides in mRNA that are read together

38
Q

How many possibilities of codons can form from 4 nucleotides?

A

64 = 4^3

39
Q

What does it mean that the genetic code is degenerate?

A

It means that more than one codon can encode for one amino acid.

40
Q

What is the start codon?

A

AUG = Methionine . It is the first codon that a ribosome reads to initiate translation.

41
Q

What are the three stop codons?

A

UAA
UAG
UGA
These tell the ribosome to terminate translation.

42
Q

What is the Wobble Hypothesis?

A

That the 3rd position on a codon has some wobble room but the first two codon positions tend to be conserved.

43
Q

What are nonsense mutations?

A

They introduce stop codons and have deleterious effect on the protein product.

44
Q

What were the hypothesized mechanisms of DNA Replication? Which one was correct?

A

Conservative - one completely new molecule and one conserved (old) DNA molecule

Dispersive - both old and new DNA molecules would have sections of old and new DNA

Semi-Conservative - both and new DNA molecules would each contain one old and one new strand. This one was correct.

45
Q

What did the Meselson-Stahl experiment do?

A

It supported semi-conservative replication by using N^15 to find out. It said that one strand of the parent DNA molecule is conserved in every new DNA molecule

46
Q

How many origins of replication do bacteria have?

A

One. It is a specific sequence that’s recognized by pre-replication complex. The replication proceeds in both directions along the circular bacterial chromosome.

47
Q

How many origins of replication do eukaryotes have?

A

Multiple. DNA replication produces an identical sister chromatid that’s connected to the original DNA molecule at the centromere of a chromosome.

48
Q

Which enzymes make DNA Replication possible?

A 
Helicase
Single-Stranded DNA Binding Proteins
Topoisomerase (DNA Gyrase)
Primase
DNA Polymerase
DNA Ligase
49
Q

What is the main function of Helicase?

A

It unwinds the two strands of DNA (helix) at the replication fork.

50
Q

What is the main function of Single-Stranded DNA Binding Proteins?

A

They are proteins that latch onto the newly separated strands and prevent them from coming back together.

51
Q

What is the main function of Topoisomerase (DNA Gyrase)?

A

It alleviates supercoiling created by helicase by making incisions in one of the DNA strands and then rotating the cut strand around the other and rejoining them to relax the DNA.

52
Q

What is the main function of Primase?

A

It synthesizes a short RNA primer that has a free 3’ hydroxyl group that is used as a starting point for the synthesis of a new strand. Supports that RNA might have held genetic material before DNA

53
Q

What is the main function of DNA polymerase?

A

It performs DNA synthesis. It travels along one of the separated DNA strands and adds nucleotides sequentially, after RNA primer at 5’ to 3’ direction.

54
Q

What is the main function of DNA Ligase?

A

It bridges together the gaps in the Okazaki fragments on the lagging strands. Forms phosphodiester bonds?

55
Q

Which way is the DNA template strand read?

Which way is DNA synthesized?

A

Read - 3’ to 5’

Synthesized - 5’ to 3’

56
Q

What are the main differences between leading and lagging strands?

A

Leading strand - has polymerase moving towards helicase/replication fork.

Lagging strand - has polymerase moving away from helicase/replication fork. DNA fragments formed in the lagging strands are known as Okazaki fragments.

57
Q

What are the main prokaryotic DNA polymerases and what are their main function? (use numbers)

A

DNA Polymerase I - Removes RNA primer, replaces primer with DNA, and repairs DNA

DNA Polymerase II - Repairs DNA

DNA Polymerase III - Main enzyme. Synthesizes new DNA and proofreads DNA via 3’ to 5’ exonuclease activity (ability to remove nucleotides one at a time from the end of a chain)

58
Q

What are the main eukaryotic DNA polymerases and what are their main function? (use Greek symbols)

A

DNA Polymerase α - Initiates DNA synthesis

DNA Polymerase δ - Synthesizes new DNA and replaces RNA primer with DNA

DNA Polymerase ε - Extends leading strand and repairs DNA

DNA Polymerase β - Repairs DNA

DNA Polymerase γ - Replicates mitochondrial DNA

59
Q

What is telomerase?

A

A special type of DNA polymerase that extends telomeres which are repetitive sequences at the ends of eukaryotic chromosomes.

60
Q

What is something RNA can do that DNA can’t.

A

RNA is capable of catalyzing biochemical reactions while DNA molecules cannot.

Biology MCAT (6 decks)

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