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Molecular Biology - Unit 1 - Zach H. > Lecture 1: DNA Chromosomes and Genomes 1 > Flashcards

Lecture 1: DNA Chromosomes and Genomes 1 Flashcards

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1
Q

What are genes?

A

The information-containing elements that determine the characteristics of a species.

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2
Q

Look over S strain and R strain experiment that was used to discover that DNA carried the hereditary information.

A

Keep Working Hard

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3
Q

What type of linkage are nucleotides joined together by?

A

phosphodiester linkage between 5’ and 3’ carbon atoms to form nucleic acids

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4
Q

Polynucleotides have a polarity, what are they?

A
  • 5’ phosphoryl end
  • 3’ hydroxyl end

** remember: read strand 5’ to 3’ **

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5
Q

What is a nucleotide?

A

A 5-carbon sugar and nitrogenous base covalently linked via a glycosidic bond.

  • sugar in DNA is deoxyribose
  • adenine, cytosine, guanine, and thymine are bases
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6
Q

How many base-pairs make up 1 turn of the double helix strand?

A

1 turn every 10 base-pairs

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7
Q

What does antiparallel mean?

A

antiparallel -> each strand’s sequence is complementary to its partner.

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8
Q

Which 2 nitrogenous bases are purines?

A
  • adenine
  • guanine
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9
Q

Which 2 nitrogenous bases are pyrimidines?

A
  • cytosine
  • thymine
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10
Q

How many hydrogen bonds are between guanine and cytosine pairs? How about adenine and thymine pairs?

A
  • Adenine pairs with Thymine = 2 H-Bonds
  • Guanine pairs with Cytosine = 3 H-bonds
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11
Q

What does genome reger to?

A

Genome -> a complete set of information in an organism’s DNA.

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12
Q

True or False:

At replication, the entire genome must be duplicated and passed to the daughter cell.

A

True

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13
Q

What two things did the discovery of the structure of DNA provide a mechanism for?

A
  • complimentary strands allow the genome to be replicated
  • each strand serves as the template
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14
Q

True or False:

Each chromosome is a single long linear DNA molecule associated with proteins that fold and pack it into compact structure.

A

True

* similar to packing 24 miles of thread into a tennis ball *

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15
Q

What does chromatin consist of?

A

DNA + Protein = Chromatin

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16
Q

Which two cell types does not contain two copies of each chromosome (maternal and paternal homologs)?

A
  • Germ Cells
  • RBCs
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17
Q

How many nucleotides and chromosomes is the human genome composed of?

A

The human genome is 3.2 x 10^9 nucleotides distributed over 24 different chromosomes.

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18
Q

What type of chromosomes make up the 46 total chromosomes in a normal phenotypic person?

A
  • 22 pairs of autosomes and 2 sx chromosomes
    • 46 total chromosomes
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19
Q

Which type of stain is used in cytogenetics laboratories for karyotype analysis of chromosomes?

A

Giemsa Stain

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20
Q

What is giemsa stain used for in cytogenetics laboratories?

A
  • the banding pattern can be seen with Giemsa stain under light microscopy
  • allowed chromosomes to be identified and numberd
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21
Q

Other than using Giemsa stain, what other cytogenetic technique can be applied to distinguish chromosomes apart?

A

Whole Chromosome Painting

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22
Q

What is whole chromosome painting useful for?

A

Useful for looking at translocations (an abnormal recombination event).

23
Q

What type of chromosome and disease does the translocation of chromosomes 9 and 22 result in?

A
  • Philadelphia Chromosome
  • Commonly found in chronic myelogenous leukemia
    • BCR-ABL fusion gene
24
Q

What information is found on chromosomes?

A
  • Genes
    • encoding proteins
    • encoding RNA molecules
  • Interspersed DNA that does not contain genes
    • regulatory information
    • “Junk” DNA
25
Q

About how many genes code for proteins in the human genome?

A

21,000

26
Q

What is the largest number of exons per gene in the human genome?

A

178

27
Q

What is the smallest number of exons per gene in the human genome?

A

1

28
Q

About what percetage of a gene comprises a coding region? Also, what percentage of that is transcribed, but not translated?

A

5%

  • 1.5% is percentage of DNA sequence in exons (protein-coding sequence)
  • 3.5% percentage of DNA in other highly conserved sequences
    • transcribed, but not translated
29
Q

What happens to chromosomes during interphase?

A

Chromosomes are replicated; they are decondensed and can’t be easily distinguished.

30
Q

What happens to chromosomes during mitosis?

A

They become highly condensed and separated into two daughter nuclei.

31
Q

What are the three requirements in order to be a chromosome?

A
  • A copy must be passed on to each daughter cell at division: requires replication, separation of copies, and partitioning to daughter cells.
    1. DNA replication origin: where duplication of the DNA begins.
    2. Centromere: allows one copy of each duplicated and condensed chromosomes ot be pulled into each daughter cell when the cell divides.
      • The kinetochore protein complex attaches to the centromere.
    3. Telomeres: at the ends of a chromosome, contain repetitive sequences that enable the ends to be efficiently replicated.
32
Q

How much more condensed are mitotic chromosomes than interphase DNA?

A

500 times

33
Q

What type of DNA binding proteins are involved in forming chromosomes?

A

Histones and non-histone chromosomal proteins.

34
Q

What is a nucleosome?

A

The most basic unit of chromosome packing is the nucleosome.

  • chromatin isolated directly from interphase nucleus forms 30 nm thick thread
  • if partially unfolded it forms “beads on a string” (string = DNA; beads = DNA wound around histones)
35
Q

How does digestion of DNA by nucleases work?

A

Digestion with nucleases break down DNA by cutting between nucleosomes and degrading the exposed DNA between nucleosome core particles (linker DNA).

36
Q

How many histone proteins does each individual nucleosome core particle consist of?

A

8 Histone Proteins (histone octamer) and 2X stranded DNA that is 147 nucleotide pairs long.

37
Q

What sub-units compose a histone octamer?

A

2 molecules each of H2A, H2B, H3, and H4

38
Q

About how many nucleotide pairs long do nucleosomes repeat?

A

Repeat every 200 nucleotide pairs or so.

39
Q

What are histones?

A

Histones are small proteins with common structural motif called histone fold.

40
Q

True or False:

A high resolution structure of nucleosome core particle is disc-shaped with DNA wrapped 2.0 turns.

A

False - high resolution structure of nucleosome core particle is disc-shaped with DNA wrapped 1.7 turns.

41
Q

What regulation is controlled by covalent modifications on the N-terminal amino acid tail that extends out from the nucleosome core particle?

A

Important for chromatin regulation.

42
Q

How many hydrogen bonds are formed between DNA and the histone core in each nucleosome?

A

142

43
Q

What type of interactions are there between DNA and histones?

A
  • hydrogen bonding
  • hydrophobic interactoins
  • salt linkages
44
Q

True or False:

Histones are highly conserved, and thus, most canges would be lethal.

A

True

** there are only 2 differences between pea and cow H4**

45
Q

What do histone tails function to do?

A

Histone tails help to condense chromatin.

  • histone tails are largely unstructured, suggesting that they are highly flexible.
  • tails can form interactions with adjacent nucleosomes
46
Q

What does the histone subunit H1 do?

A

changes the path of the DNA as it exits the nucleosome

47
Q

What are the characteristics of histone H1?

A
  • linker histone
  • larger than other histone proteins
    • also less well conserved
  • contacts both DNA and protein
  • changes the path of the DNA as it exits the nucleosome
48
Q

True of False:

Nucleosomes are in a constant state of flux.

A

True

*DNA is unwrapped in the nucleosome 4 times per second, and remains unwrapped for 10-50 milliseconds before tightening up again*

49
Q

What do chromatin remodeling complexes allow for?

A

Further loosening of DNA/histone contact.

50
Q

What changes the structure of the nucleosome temporarily, making DNA less tightly bound?

A

The ATP-dependent chromatin remodeling complex.

51
Q

Look over the chromatin remodeling mechanism to understand how the DNA is made available to other proteins in the cell.

A
52
Q

What does the proposed zig-zag model explain?

A

Nucleosome Packing

  • stacking may be facilitated by histone tails (esp H4)
  • histone H1 “linker histone” is present in 1:1 ratio with nucleosome cores

** forms a dense fibrous structure with a diameter of 30 nm **

53
Q
A

Molecular Biology - Unit 1 - Zach H. (5 decks)

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