Macromolecules of the Cell - Nucleic Acids, Structure & Function

Question 1

What does DNA stand for?

Answer 1

DeoxyriboNucleic Acid.

Question 2

The main role of DNA in the cell is the long-term storage of …………….. .

Answer 2

Information.

Question 3

All known cellular life and all known viruses contain DNA - true or false?

Answer 3

False. All known cellular life does contain DNA, but only some viruses contain DNA.

Question 4

In vertebrates, which cells do not contain DNA, because their nuclei are lost when the cells are made?

Answer 4

Erythrocytes (red blood cells).

Question 5

What are the five nitrogenous bases found in DNA?

Answer 5

Cytosine, thymine, uracil (in RNA), adenine and guanine.

Question 6

What are the two categories of nitrogenous bases? What are the differences between the two?

Answer 6

Pyramidines - one ring in the atom.

Purines - two rings in the atom.

Question 7

Name the three pyramidine nitrogenous bases.

Hint: CUt The PYe!

Answer 7

Cytosine, uracil and thymine.

Question 8

Name the two purine nitrogenous bases.

Hint: PURe As Gold!

Answer 8

Adenine and guanine.

Question 9

Besides the nitrogenous base, what are the two other components of DNA?

Answer 9

Phosphate and deoxyribose.

Question 10

Deoxyribose is a …………. sugar with … -group on the second carbon atom.

Answer 10

Pentose, hydrogen.

Question 11

A nitrogenous base linked to a sugar is known as a ……………. ?

Answer 11

Nucleoside.

Question 12

What sort of linkages join nitrogenous bases to deoxyribose in a nucleoside?

Answer 12

N-glycosidic linkages.

Question 13

Which carbon of deoxyribose is a nitrogenous base bonded to with an n-glycosidic linkage in a nucleoside?

Answer 13

C 1’.

Question 14

Where are phosphates added to nucleosides to form nucleotides?

Answer 14

At C 5’ of the sugar (top of the pentagon).

Question 15

Name some biochemical uses of nucleotides.

Answer 15

1. Chemical energy - ATP is a nucleotide.
2. It is a product of phosphorylation and cellular respiration.
3. Used in motility and cell division.
4. Signal transduction pathways and secondary messenger systems.

Question 16

In the DNA structure, the two strands run antiparallel - what does this mean?

Answer 16

They run in opposite directions - one from the 5’ to the 3’ end and one from the 3’ to the 5’ end.

Question 17

True or false? One strand of DNA has purines (adenine and guanine), the other side has pyramidines (thymine and cytosine).

Answer 17

True.

Question 18

Which DNA bases always pair together?

Answer 18

Adenine / thymine.

Cytosine / guanine.

Question 19

How many hydrogen bonds are there between adenine and thymine?

Answer 19

Two.

Question 20

How many hydrogen bonds are there between cytosine and guanine?

Answer 20

Three.

Question 21

What implications does the difference in the number of hydrogen bonds between adenine and thymine (two) and cytosine and guanine (three) have?

Answer 21

Although the H-bonds are relatively easy to break, it is slightly easier to break the two bonds between adenine and thymine than it is to break the three bonds between cytosine and guanine.

Question 22

By convention, DNA base pairs are always written from which end?

Answer 22

From the 5’ end to the 3’ end.

Question 23

True or false? Watson and Crick’s 1953 paper was the first time genes and DNA were known about?

Answer 23

False. They discovered DNA’s double helix structure, but genes and DNA were alreaday known about prior to 1953.

Question 24

What is the minor groove and the major groove?

Answer 24

The minor groove is where the turns of the DNA doube helix are closer together; the major groove is where they are further apart.

Question 25

What is being described here?

Formed from DNA and protein, they resemble ‘beads on a string’ when viewed under an electron microscope.

The ‘beads’ are nucleosomes made of DNA wrapped around a protein core.

Answer 25

Chromatin.

Question 26

What is Chargraff’s First Rule?

Answer 26

That in any dsDNA molecule, the amount of guanine equals the amount of cytosine and the amount of adenine equals the amount of thymine.

Question 27

Are there always equal amounts of cytosine / guanine to adenine / thymine in a dsDNA molecule?

Answer 27

Not necessarily, no.

Question 28

What happens if a dsDNA molecule has a higher proportion of cytosine / guanine than of adenine / thymine?

Answer 28

It is more difficult to pull apart because there are more of the triple hydrogen bonds that hold cytosine and guanine together.

Question 29

As genomes, DNA can take three forms - name them.

Answer 29

1. Single stranded DNA (ssDNA). Found in some viruses.
2. Double stranded loop (dsDNA). In bacteria, viruses, mitochondria and chloroplasts.
3. Double stranded linear (dsDNA). In most eukaryotic cells.

Question 30

True or false - the size and complexity of an organism depends on the number of genes that it has. The bigger and more complex the organism, the more chromosomes there are in its genome.

Answer 30

False. The size and complexity of an animal has no bearing on the number of chromosomes it has.

Question 31

What is DNA complexed with to form nucleosomes, the next level of chromosome structure?

Answer 31

Histones. Each nucleosome consists of eight histone proteins. The DNA wraps around these 1.65 times.

Question 32

What is a chromatosome formed of?

Answer 32

A nucleosome plus the H1 histone.

Question 33

Chromatosomes are folded, looped, compressed and tightly coiled to form the tightly condensed DNA in a ……………. ?

Answer 33

Chromatid.

Question 34

Put the levels of chromosome structure in the correct order:

Histone
Nucleosome
Chromatosome
Chromosome
Chromatin
H1 Histone
Chromatid.

Answer 34

1. Chromatin.
2. Histone + nucleosome.
3. Nucleosome + H1 histone.
4. Chromatosome.
5. Chromatid.
6. Chromosome.

Question 35

How much of the DNA of animals and plants is in the nucleus? Where in the cell is the rest found?

Answer 35

99% of the DNA of animals and plants is found in the nucleus. The rest is found in the mitochondria (of animals) and the chloroplasts (of plants).

Question 36

Where is the DNA of bacteria found?

Answer 36

Free-floating in the cytoplasm.

Question 37

How does the structure of RNA differ from DNA?

Answer 37

The sugar in RNA is ribose intead of deoxyribose - the hydrogen atom on C 2’ is replaced by an OH.

Thymine bases are replaced by uracil.

Question 38

Is RNA more or less stable than DNA?

Answer 38

RNA is less stable than DNA. Because of the OH group on C 2’ of the sugar, it is susceptible to hydrolysis.

This is why vaccines based on RNA are cold-sensitive.

Question 39

RNA is ……………. -stranded. This means that it can …………. into a variety of different …………. .

Answer 39

Single, fold, shapes.

Question 40

What are the three types of RNA?

Answer 40

Ribosomal RNA (rRNA), transfer RNA (tRNA) and messenger RNA (mRNA).

Question 41

Which RNA is this?

Many hundreds of different types in each cell.
Only a few copies of each type.
Very few uncommon bases.
Heterogenous size population 6S to 25S.

Answer 41

mRNA.

Question 42

Which RNA is this?

The smallest RNA.
Contains 10% uncommon bases.
Many dfferent types in each cell.
Multiple copies of each different type within the cell.
Commonly has a clover leaf structure.

Answer 42

tRNA.

Question 43

Which RNA is this?

Few types.
Occurs in very high numbers.
Very few uncommon bases.

Sizes in bacteria: 5S, 13S and 23S.
Sizes in mammalian cytoplasm: 5S, 7S, 18S and 28S.
Sizes in mammalian mitochondria: 16S, 18S.
Sizes in plant cytoplasm: 5S, 8S, 24S-28S.
Sizes in plant chloroplasts: 5S, 16S, 23S.

Answer 43

rRNA.

Question 44

What are Svedberg numbers (S)?

Answer 44

Svedberg numbers are used to describe the size of RNA - the higher the Svedberg number, the larger the molecule.

Svedbergs are calculated using sedimentation in a centrifuge.