20.2 - the structure of DNA & RNA

Question 1

A single strand of DNA is a polymer of nucleotides bonded to one another by

Answer 1

3′–5′ phosphodiester bonds.

Question 2

The backbone of the polymer is called the

Answer 2

sugar-phosphate backbone

Question 3

why is it called sugar-phosphate backbone

Answer 3

because it is composed of alternating units of the five-carbon sugar 2′-deoxyribose and phosphoryl groups in phosphodiester linkage.

Question 4

A nitrogenous base is bonded to each sugar by an

Answer 4

N-glycosidic linkage

Question 5

DNA is a _____- of two strands of DNA wound around one another.

Answer 5

double helix

Question 6

The structure of the double helix is often compared to a

Answer 6

spiral staircase

Question 7

The sugar-phosphate backbones of the two strands of DNA spiral around the ______- like the handrails on a spiral staircase.

Answer 7

outside of the helix

Question 8

the nitrogenous bases extend into the ____ at ___ angles to the ___of the helix.

Answer 8

center
right
axis

Question 9

One noncovalent attraction that helps maintain the double helix structure is

Answer 9

hydrogen bonding between the nitrogenous bases in the center of the helix.

Question 10

_____-forms two hydrogen bonds with ___, and _____forms three hydrogen bonds with ____

Answer 10

adenine, thymine

cytosine, guanine

Question 11

adenine thymine
cytosine guanine
are called

Answer 11

base pairs

Question 12

The two strands of DNA are

Answer 12

complementary strands

Question 13

why are they called complementary strands

Answer 13

because the sequence of bases on one automatically determines the sequence of bases on the other.

Question 14

When there is an adenine on one strand, there will always be a thymine in the ____location on the ____ strand.

Answer 14

same

opposite

Question 15

The diameter of the double helix is

Answer 15

2 nm

Question 16

what dictates the diameter of the double helix

Answer 16

by the dimensions of the purine-pyrimidine base pairs.

Question 17

The helix completes one turn every

Answer 17

10 base pairs

Question 18

One complete turn is

Answer 18

3.4 nm

Question 19

each base pair advances the helix by

Answer 19

0.34 nm

Question 20

the DNA double helix is that the two strands are

Answer 20

antiparallel strands

Question 21

antiparallel strands meaning

Answer 21

the two strands of the helix run in opposite directions

Question 22

only when the two strands are _____ can the base pairs form the hydrogen bonds that hold the two strands together.

Answer 22

antiparallel

Question 23

Chromosomes

Answer 23

are pieces of DNA that carry the genetic instructions, or genes, of an organism

Question 24

Organisms such as the prokaryotes have only a ____ chromosome, and its structure is relatively simple. Others, the eukaryotes, have ____ chromosomes, each of which has many different levels of structure.

Answer 24

single

many

Question 25

The complete set of genetic information in all the chromosomes of an organism is called the

Answer 25

genome

Question 26

are organisms with a simple cellular structure in which there is no true nucleus surrounded by a nuclear membrane and there are no true membrane-bound organelles.

Answer 26

prokaryotes

Question 27

bacteria are

Answer 27

prokaryotes

Question 28

in prokaryotic organisms the chromosome is a ___________ that is ______, which means that the helix is coiled on itself.

Answer 28

circular DNA molecule

supercoiled

Question 29

The supercoiled DNA molecule is attached to a complex of proteins at roughly ____ sites along its length, forming a series of loops. This structure, called the ______

Answer 29

40

nucleoid

Question 30

are organisms that have cells containing a true nucleus enclosed by a nuclear membrane

Answer 30

Eukaryotes

Question 31

all animals, plants, and fungi are

Answer 31

eukaryotes

Question 32

humans have ____ pairs of chromosomes, while the adder’s tongue fern has ____ pairs of chromosomes.

Answer 32

23

631

Question 33

what is the first level structure of eukaryotic chromosome structure

Answer 33

nucleosome

Question 34

what does a nucleosome consist of

Answer 34

a strand of DNA wrapped around a small disk made up of histone proteins.

Question 35

what does the DNA look like at the nucleosome level

Answer 35

DNA looks like beads along a string.

Question 36

nucleosome coils into a larger structure called

Answer 36

condensed fiber

Question 37

This complex of DNA and protein is termed (condensed fiber)

Answer 37

chromatin

Question 38

chromatin makes up what

Answer 38

the eukaryotic chromosome

Question 39

Some human genetic disorders are characterized by

Answer 39

unusual chromosome #s

Question 40

Down syndrome is characterized by an

Answer 40

extra copy of chromosome number 21

Question 41

The presence of an additional chromosome 18 causes

Answer 41

Edward syndrome

Question 42

extra chromosome 13

Answer 42

Patau syndrome

Question 43

The presence of extra copies of the sex chromosomes, X or Y, is

Answer 43

not lethal

Question 44

Males with two X chromosomes and one Y suffer from

Answer 44

Klinefelter syndrome and show sexual immaturity and breast development

Question 45

Males with an extra Y chromosome are

Answer 45

unusually tall

Question 46

women with three X chromosomes

Answer 46

unusually tall

Question 47

A woman with only a single X chromosome experiences

Answer 47

turner syndrome

Question 48

The sugar-phosphate backbone of RNA consists of

Answer 48

also linked by 3′–5′ phosphodiester bonds.

Question 49

RNA molecules differ from DNA molecules in three basic properties.

Answer 49

RNA molecules are usually single-stranded.

The sugar-phosphate backbone of RNA consists of ribonucleotides linked by 3′–5′ phosphodiester bonds. Thus, the sugar ribose is found in place of 2′-deoxyribose.

The nitrogenous base uracil (U) replaces thymine (T).

Question 50

Although RNA molecules are single-stranded, base-pairing between uracil and adenine and between guanine and cytosine

Answer 50

can still occur