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Biochemistry > DNA Structure > Flashcards

DNA Structure Flashcards

1
Q

(Euchromatin/Heterochromatin) contains genes that the cell frequently transcribes and is loosely packed.

A

Euchromatin

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2
Q

The cytosine and guanine base pair is held together by (number) hydrogen bonds.

A

Three

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3
Q

The DNA strands are said to run to each other because they each run in opposite directions.

A

antiparallel

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4
Q

The liquid environment inside the nucleus is called the .

A

nuclopplasm

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5
Q

are thin filamentous proteins that form the nuclear lamina and create a dense protein web within the nucleus

A

Lamin proteins

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6
Q

Nitrogenous bases that contain one ring are called (purines/pyrimidines) .

A

pyrimidines

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7
Q

A is a structure component of nucleic acids that consists of a phosphate group, a sugar, and a nitrogenous base.

A

Nucleotide

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8
Q

The base pairs between DNA helical strands are held together by bonds.

A

hydrogen

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9
Q

Nitrogenous bases that contain two rings are called (purines/pyrimidines) .

A

purines

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10
Q

Chromatin is usually made up of (number) chromosomes in humans.

A

46

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11
Q

The is the structure inside the nucleus of the cell that makes ribosomes.

A

nucleolus

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12
Q

The adenine and thymine base pair is held together by (number) hydrogen bonds.

A

two

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13
Q

(Euchromatin/Heterochromatin) contains rarely transcribed genes and is densely packed.

A

Heterochromatin

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14
Q

What is the difference between a nucleotide and a nucleoside?

A

Only nucleotides have a phosphate group.

Both nucleotides and nucleosides contain a nitrogenous base and a pentose sugar. However, nucleotides contain an additional phosphate group.

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15
Q

Which component of DNA gives it its negative charge?

A

Phosphate

DNA’s negative charge is due to its phosphate backbone.

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16
Q

Which of the following is correct?

A

Purines: Adenine and Guanine
Pyrimidines: Cytosine, Uracil, & Thymine

Purines = Adenine, Guanine

Pyrimidines = Cytosine, Thymine, Uracil

Mnemonic: The purines and pyrimidines can be remembered with the phrases “Pure AG (silver)” and “CUTie Py”: purine = AG, CUT = pyrimidine.

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17
Q

Which nucleotide base is swapped for thymine in RNA?

A

Uracil

Nucleotides of DNA = A, T, G, C Nucleotides of RNA = A, U, G, C

DNA contains thymine, whereas RNA contains uracil.

18
Q

Which of the following is a correct base pairing?

A

Adenine to Uracil (RNA)
Adenine to Thymine (DNA)

Purines (A, G) will always pair with pyrimidines (T, U, C).

Correct base pairings:

A-T (DNA)

A-U (RNA)

G-C (DNA or RNA)

19
Q

Which of the following has the strongest bond?

A

Guanine to Cytosine

G-C pairs are the strongest as they have three hydrogen bonds, while A-T pairs and A-U pairs have two hydrogen bonds.

20
Q

New nucleotides are added to which hydroxyl group of the pentose sugar at the end of a DNA strand?

A

3’ end of the growing DNA strand

DNA is said to elongate in the 5’ → 3’ direction. The phosphate group attached to the 5’ carbon of a newly joining nucleotide engages in a condensation reaction with the 3’ hydroxyl group of the nucleotide at the end of the DNA strand, forming a phosphodiester bond.

21
Q

New nucleotides are added to the chain of DNA via condensation reactions catalyzed by which enzyme?

A

DNA Polymerase

DNA polymerase catalyzes the addition of new nucleotides to an existing chain through condensation reactions.

22
Q

________ has an extra -OH on its sugar’s 2’ carbon, thereby making the structure ________ vulnerable to hydrolysis.

A

RNA; more

Ribose (in RNA) has an extra 2’ hydroxyl group compared to deoxyribose (in DNA). This is why RNA is less stable than DNA!

Remember: DeOXYribonucleic acid = one less -OH group as compared to RNA.

23
Q

Which two amino acids predominately give histones their positive charge?

A

Arginine and lysine are the two amino acids that give histones their positive charge.

Histones have a positive charge, allowing them to attract negatively charged DNA.

Mnemonic: Basic/positively charged amino acids can be remembered with the phrase “HIS LYS (lies) ARe basic”: HIStidine, LYSine, & ARginine (except histidine has no charge at body pH).

24
Q

Which histone subunit is not part in the histone core?

A

H1

H1 protein is not in the core but is instead the linker protein between histone octameric cores.

The histone octameric core consists of subunits H2A, H2B, H3, and H4.

25
Q

Which of the following describes a single unit of DNA wrapped around a single histone core?

A

Nucleosome

Nucleosomes are basic structural units of packaged DNA; chains of them will resemble “beads on a string” because each nucleosome is DNA wrapped around a histone core.

26
Q

Compared to heterochromatin, euchromatin is ______ compact and expressed ______.

A

less; more

As a result of euchromatin being less compact, there is more room for enzymes to access the DNA and transcribe it.

Heterochromatin will be much more compact, making it less transcribed as a result.

Mnemonic: Euchromatin is Expressed; Heterochromatin is Hindered.

27
Q

Which of the following outcomes is typically associated with methylation of DNA?

A

Decreased gene expression

DNA methylation usually involves the addition of a methyl group to C5 of cytosine. This modification typically mutes DNA, which is to say it decreases gene expression.

Key Takeaway:
DNA methylation → decreased expression

28
Q

Histone acetylation usually ________ transcription by ________ the DNA coils around the histones.

A

increases; loosening

Histone acetylation would remove the positive charge from histones. As a result, negatively charged DNA will bind more loosely to the histones, making the DNA more accessible to enzymes for increased transcription.

Mnemonic: Histone Acetylation = Activation (increased DNA expression).

Key Takeaway:
DNA methylation → decreased DNA expression
Histone acetylation → increased DNA expression

29
Q

A researcher is studying a dermatologic disease variably expressed in different anatomic regions and takes samples from several locations. She finds that normal patches of skin have the mutant gene localized to the periphery of the nucleus in dense, closely packed regions of chromatin. Which of the following cellular mechanisms is most directly affected by this method of DNA organization?

A

Transcription

The localization of the gene to a dense, closely packed region of chromatin suggests the mutant gene is sequestered in heterochromatin. The closely packed superstructure of heterochromatin renders genes less accessible to transcriptional machinery, thereby decreasing gene expression. It consists of heavily methylated DNA and deacetylated histones.

30
Q

An investigator is studying the effects of chromatin structure on genetic regulation. Electron microscopy of an eukaryotic cell during interphase reveals 10 nm thick chromatin fibers with a “beads on a string” appearance. The “beads” are composed of DNA wrapped around a core of proteins. These proteins are rich in which of the following?

A

Lysine and Arginine

Phosphate provides DNA with an overall negative charge. Proteins that associate closely with DNA (histones) have abundant positively-charged amino acids including lysine and arginine.

During the initial steps of DNA packaging into chromatin, negatively charged DNA double helix wraps around the positively charged histone core twice. In general, there are three levels of chromatin organization:

31
Q

A researcher is studying the structure of the nucleus under an electron microscope. He detects an area of heterochromatin, at the periphery of the nucleus that he identifies as the inactivated X-chromosome (the Barr body). Which of the following cellular mechanisms best explains the appearance of this structure on electron microscopy?

A

Histone methylation

Histone methylation is the process of adding methyl groups to histone subunits of the nucleosome (DNA, histone complex). Methylation is largely responsible for the appearance of heterochromatin (tightly packed DNA) on electron microscopy and contributes to the formation of the Barr body (inactivated X chromosome) in females.

In addition, the Barr body undergoes DNA methylation–a form of irreversible gene silencing without actually changing the sequence of DNA. Similar to histone methylation, DNA methylation causes tight coiling of DNA around histones. Both DNA methylation and histone methylation lead to the condensed and sterically inaccessible form of DNA called heterochromatin, which is located typically at the periphery of the nucleus.

32
Q

Which two amino acids predominately give histones their positive charge?

A

Arginine and lysine

Histones have a positive charge, allowing them to attract negatively charged DNA.

Arginine and lysine are the two amino acids that give histones their positive charge.

Mnemonic: Basic/positively charged amino acids can be remembered with the phrase “HIS LYS (lies) ARe basic”: HIStidine, LYSine, & ARginine (except histidine has no charge at body pH).

33
Q

Which histone subunit is not part in the histone core?

A

Histone H1

H1 protein is not in the core but is instead the linker protein between histone octameric cores.

The histone octameric core consists of subunits H2A, H2B, H3, and H4.

34
Q

Which of the following describes a single unit of DNA wrapped around a single histone core?

A

Nucleosome

Nucleosomes are basic structural units of packaged DNA; chains of them will resemble “beads on a string” because each nucleosome is DNA wrapped around a histone core.

35
Q

Compared to heterochromatin, euchromatin is ______ compact and expressed ______.

A

less; more

36
Q

The pyrimidine thymine (T) is DNA-specific, and is RNA-specific.

A

Uracil

37
Q

The five carbon sugar in DNA is deoxyribose and the one in RNA is .

A

ribose

38
Q

The 3 pyrimidine nucleobases are .

A

cytosine, or C, thymine, or T, and uracil or U

39
Q

The 2 purine nucleobases are .

A

adenine, or A, and guanine, or G

40
Q

Nucleotides are the building blocks of .

A

nucleic acids (DNA and RNA)

41
Q

A nucleoside becomes a nucleotide when a molecule is added.

A

phosphate

42
Q

The 3 subunits of a nucleotide are .

A

a five carbon sugar, a phosphate group, and a nitrogenous base

Biochemistry (9 decks)

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