Chapter 5: DNA and Chromosomes

Question 1

Base + sugar + phosphate =

Answer 1

nucleotide, the monomer subunit of DNA (polymer of nucleotides)

Question 2

Base + sugar =

Answer 2

nucleoside

Question 3

Why is DNA referred to as 5’ -> 3’?

Answer 3

This is the order DNA is replicated

Question 4

Purines

Answer 4

• 2 ring structures
• Adenine
• Guanine

Question 5

Pyrimidines

Answer 5

• 1 ring structure
• cytosine
• thymine

Question 6

How are bases paired?

Answer 6

Adenine and Thymine, can form 2 hydrogen bonds

Guanine and Cytosine, can form 3 hydrogen bonds

Question 7

DNA vs RNA structure

Answer 7

Both: have nitrogenous base connected to 1’ end, and phosphate attached to 5’ end to lead to the next nucleotide connection

DNA has H on 2’ end, while RNA has OH group on 2’

Question 8

Describe formation of DNA

Answer 8

• phosphodiester bonds between 3’ (OH) and 5’ (PO3) carbons on deoxyribose
• 2 strands held together in double helix by hydrogen bonds between complimentary base pairs
• strands MUST run antiparallel
• leaves 3’ end OH group and 5’ end phosphate group on opposite ends

Question 9

How does DNA encode genes?

Answer 9

• DNA is transcribed to RNA
• some RNAs are translated to direct the production of specific protein molecules, some have RNA as the final product

Question 10

What two reactions are the most frequent spontaneous chemical reactions known to cause DNA damage in cells?

Answer 10

Deamination and Depurination, both involved hydrolysis

Question 11

Depurination

Answer 11

disruption of bond, causes base to be removed and left with depurinated sugar

purine bases - A or G - removed and leaves phosphate and sugar alone

Question 12

Deamination

Answer 12

-removal of an amino group

Question 13

How is DNA packaged?

Answer 13

in heterochromatin and euchromatin

pattern of:

heterochromatin/telomere -> euchromatin -> heterochromatin/centromere -> euchromatin…….

goes on until end, which will be heterochromatin/telomore

Question 14

Heterochromatin

Answer 14

firmly/densely packed part of chromosomes that is genetically inactive

consists of a telomeres and centromeres

Question 15

Euchromatin

Answer 15

uncoiled, loosely packed part of chromosomes that is genetically active

Question 16

Nucleosomes

Answer 16

• basic units of eukaryotic chromosome structure
• contain DNA wrapped around a protein core of eight histone molecules

Question 17

What are histones?

Answer 17

• contain many basic amino acids (lysine, arginine), have + charge

Question 18

Explain structure of DNA with histone proteins

Answer 18

• “beads on a string”
• histones wrapped in form of chromatin, with nucleosome including approx. 200 nucleotide pairs of DNA
• each histone has space for linker DNA in between them
• nucleosome released from digestion of linker DNA by nuclease
• ## only exposed linker DNA digested, not those wrapped around nucleosome core

Question 19

Histone code

Answer 19

a hypothesis which states that DNA transcription is largely regulated by post-translational modifications to these histone proteins

• Different combinations of histone tail modifications can confer a specific meaning on the stretch of chromatin on which they occur
• provides cell memory, has different chemical tags that are put on amino acids of the histones that extend out of the nucleosome

Question 20

What is cell memory based on?

Answer 20

• chromatin structure
• structure may effect gene expression, inherit when cell divides
• some genes may only act once

Question 21

Eukaryotic DNA

Answer 21

• packed into multiple chromosomes
• specialized sequences required for DNA replication and chromosome segregation
• can carry ancient sequences

Question 22

Chromosome Painting

Answer 22

• exposes the chromosomes to collection of single-stranded DNA molecules that have been coupled to comb of fluorescent dyes
• human chromosome pairs can be identified by hybridization to chromosome specific fluorescent probes
• two copies each, maternal and paternal chromosomes (homologous)

Question 23

Describe the process needed to produce a eukaryotic chromosome that can be duplicated and then segregated at mitosis

Answer 23

Each chromosome has multiple origins of replication, one centromere, and two telomeres.

The DNA replicates in interphase, beginning at the origins of replication and proceeding bidirectionally from each origin along the chromosome.

In M phase, the centromere attaches the compact, duplicated chromosomes to the mitotic spindle so that one copy will be distributed to each daughter cell when the cell divides.

Prior to cell division, the centromere also helps to hold the duplicated chromosomes together until they are ready to be pulled apart. Telomeres contain DNA sequences that allow for the complete replication of chromosome ends.

Question 24

Mobile genetic elements

Answer 24

• in genomes of nearly all organisms
• ancient viral like sequences
• can move from one position to another by transpostional or site specific recombonation

Question 25

Viruses and transposable elements

Answer 25

• put themselves into genome
• created genetic variation
• crucial for evolution

Question 26

Give an example of the histone code

Answer 26

H3K4me^3

it activates transcription

it attracts proteins that make euchromatin

Question 27

Why do histones have many amino acids that have a net positive charge?

Answer 27

it stabilizes the negative charge on the DNA sugar phosphate backbone; so DNA can be packaged tightly around the histones