4. Nucleic acids

Question 1

What are nucleotides?

Answer 1

They are biological molecules and the monomers of nucleic acids (DNA and RNA)

Question 2

What is the structure of nucleotides?

Answer 2

There is a five-carbon (pentose) sugar bonded to a phosphate group and a nitrogenous base.

Question 3

What is the pentose sugar in the nucleotide for RNA?

Answer 3

ribose

Question 4

What is the pentose sugar in the nucleotide for DNA?

Answer 4

deoxyribose

Question 5

What is a phosphorylated nucleotide?

Answer 5

A nucleotide that contains more than one phosphate group.

Question 6

What are the 4 nitrogenous bases and what are they called as part of a nucleotice?

Answer 6

adenine = adenosine
cytosine = cytosine
guanine = guanosine
thymine = thymosine

Question 7

What is it called when there is 1 phosphate group?

Answer 7

monophosphate

Question 8

What is it called when there is 2 phosphate groups?

Answer 8

diphosphate

Question 9

What is it called when there is 3 phosphate groups?

Answer 9

triphosphate

Question 10

Where is is DNA found?

Answer 10

The nuclei of all eukaryotic cells, the cytoplasm of prokaryotic cells and inside some types of viruses.

Question 11

What is the structure of DNA?

Answer 11

A polymer made up of repeating monometric units (nucleotides).
A molecule of DNA consists of 2 polynucleotide strands.
The 2 strands run in different directions, they are antiparellel.

Question 12

What is the structure of a phosphate group?

Answer 12

It contains a phosphorus atom bonded with a single covalent bond to 3 hydroxyl (OH) groups and a double covalent bond with 1 oxygen atom.

Question 13

What is the structure of ribose?

Answer 13

A pentose sugar with a hydroxyl (OH) group on carbon 1, 2, 3 and 5

Question 14

What is the structure of deoxyribose?

Answer 14

A pentose sugar with a hydroxyl (OH) group on carbon 1, 3 and 5 but a hydrogen atom on carbon 2.

Question 15

How does the phosphate group bond to the pentose sugar in a nucleotide?

Answer 15

Through a condensation reaction.
The hydroxyl (OH) group on carbon 5 of the pentose sugar and the hydrogen from one of the hydroxyl groups on the phospate group bond to release a water molecule (H20).
This forms the covalent bond.

Question 16

How does the nitrogenous base bond to the pentose sugar in a nucleotide?

Answer 16

Through a condensation reaction.
The hydroxyl (OH) group on carbon 1 of the pentose sugar and the hydrogen from the nitrogenous base bond to release a water molecule (H20).
This forms the covalent bond.

Question 17

What is a purine?

Answer 17

A nitrogenous base with two rings.

Adenine and Guanine.

Question 18

What is a pyrimidine?

Answer 18

A nitrogenous base with one ring.

Thymine, Cytosine and Uracil.

Question 19

How do the two antiparallel DNA strands join together?

Answer 19

By hydrogen bonds between the two nitrogenous bases.

Question 20

Which nitrogenous bases bond together?

Answer 20

Adenine and Thymine with two hydrogen bonds

Guanine and cytosine with three hydrogen bonds

Question 21

Why do purines always bond with pyrimidines?

Answer 21

Because it means that each pair has 3 rings (2 from the purine and 1 from pyrimidine).

Question 22

How is DNA organised in eukaryotic cells?

Answer 22

The majority of the DNA is in the nucleus.
The DNA molecules are wound around histone proteins into chromosomes.
Each chromosome is a molecule of DNA.
There is also a loop of ‘naked’ DNA inside mitochordria and chloroplasts.

Question 23

How is DNA organised in prokaryotic cells?

Answer 23

DNA is in a loop within the cytoplasm, not enclosed in a nucleus.
It is not wound around histone proteins.
It is described as naked.

Question 24

What has to happen before cell division?

Answer 24

During interphase, DNA has to be copied so that each new daughter cell receives the full set of instructions.

Question 25

How does DNA replicate?

Answer 25

By semi-conservative replication... 1) Unwinding 2) Unzipping- hydrogen bonds between nucleotides are broken. 3) Free phosphorylated nucleotides in the nucleus are bonded to the exposed bases. 4) Leading strand is synthesised continuously. Lagging strand is synthesised in fragments then later joined. 5) Phosphodiester bonds form between the sugar of one nucleotide and the phosphate group of the next.

Question 26

What enzymes are involved with DNA replication?

Answer 26

1) Unwinding is catalysed by gyrase enzyme. 2) Unzipping is catalysed by DNA helicase. 3) Formation of phosphodiester catalysed by DNA polymerase. 4) Synthesis of lagging strand catalysed by ligase enzyme.

Question 27

What is the result of semi-conservative replication?

Answer 27

2 DNA molecules, identical to each other and to the parent molecule. Each of these molecules contains one old strand and one new strand.

Question 28

How is RNA different from DNA?

Answer 28

The sugar in the nucleotides of RNA is ribose, not deoxyribose. The nitrogenous base uracil (a pyrimidine) replaces thymine. The polynucleotide chain is single-stranded. The polynucleotide chain is shorter.

Question 29

What are the 3 forms of RNA?

Answer 29

messenger (mRNA) transfer (tRNA) ribosomal (rRNA)- Used to make ribosomes and made in the nucleolus.

Question 30

How can genes carry out their function?

Answer 30

Within each gene there is a sequence of DNA base triplets that determines the amino acid sequence (primary structure) of a polypeptide. This allows it to fold correctly into its tertiary structure, enabling it to carry out its function.

Question 31

What is transcription and translation?

Answer 31

Instructions inside the genes on chromosomes cannot pass out of the nucleus so a copy of each gene has to be transcribed (copied) into a length of mRNA. This can pass out of the nucleus to the ribosome where the coded instructions are translated and the protein is assembled from amino acids.

Question 32

What are the stages of transcription?

Answer 32

1) The gene unwinds and unzips 2) Hydrogen bonds between the base pairs break. 3) Temporary hydrogen bonds form between RNA nucleotides and the nucleotides of the DNA's template strand. 4) A length of RNA that is complementary to the template strand of the gene is produced- This is an exact copy of the coding strand. 5) The mRNA passes out of the nucleus, through the nuclear envelope, and attaches to the ribosome.

Question 33

Where are transfer RNA molecules made?

Answer 33

Made in the nucleolus and pass out of the nucleus into the cytoplasm

Question 34

What is the structure of transfer RNA molecules?

Answer 34

A single RNA strand Hydrogen bonds between the bases maintains the structure. At one end is an anticodon (triplet of bases) that are complementary to the codon on the mRNA At the other end is another triplet of bases which bind to a specific amino acid which will be bound to the mRNA.

Question 35

What is the funtion of transfer RNA?

Answer 35

They bring the amino acids to the ribosome and find their complementary place on the mRNA molecule.

Question 36

Why is the genetic code described as universal?

Answer 36

Because all living organisms have the same triplet of DNA bases that code for the same amino acid.

Question 37

Why is the genetic code described as degenerate?

Answer 37

Because for almost all amino acids there is more than one base triplet. This reduces the effect of point mutations, as a change in one base could produce the same amino acid.

Question 38

Why is the genetic code described as non-overlapping?

Answer 38

It is read starting from a fixed point in groups of three bases. If a bases is added or deleted, it causes a frame shift. Every base triplet after that, and hence every amino acid coded for, is changed.