2.1.2 to 2.2

Like DNA, RNA is a ________.

polymer of nucleotides

RNA contains four nucleotides with the bases ________.

adenine (A):uracil (U):cytosine (C):guanine (G)

Unlike DNA, RNA is ________.

single-stranded

However, tRNA can fold back on itself, and ________ within the same molecule stabilizes the looped structure.

complementary base pairing

Where are all RNA molecules synthesized?

In the nucleus.

Only ________ different RNA molecules that involved in protein synthesis and their functions are listed in Table 2.1.

three

________ is the hereditary material responsible for passing genetic information from cell to cell and generation to generation.

DNA

In total, there are around ________ base pairs in the DNA of a typical mammalian cell.

3.2 billion

This vast number means that there are an almost infinite variety of ________ along the length of a DNA molecule.

sequences or bases

It is this variety that provides the ________ within living organisms.

genetic diversity

It is a very ________ which normally passes from generation to generation without change.

stable structure

Only rarely does it ________.

mutate

Its two separate strands are joined only with ________, which allow them to separate during DNA replication and protein synthesis.

hydrogen bonds

It is an extremely ________ and therefore carries a large amount of genetic information.

large molecule

By having the base pairs within the helical structure of the ________, the genetic information within the structure to some extent protected from being corrupted by outside chemical and physical forces.

deoxyribose-phosphate backbone

________ leads to DNA being able to replicate and to transfer information to mRNA.

Base pairing

The function of the remarkable molecule, DNA depends on the ________ that it possesses.

sequence of base pairs

This sequence is important to everything it does and, indeed, to ________.

life itself

________ is the making of an exact copy of the DNA molecule.

DNA replication

The replication is made by a ________ method, which was predicted by Watson and Crick and proven by Meselson and Stahl.

semiconservative

Explain why DNA replication is regarded as semiconservative.

Because each of the resulting two molecules consists of one old strand and one new strand.

________ assist in replication of DNA.

Proteins and enzymes

Replication begins at special sites called ________, the replication bubbles form.

origins of replication

________ unwind the double helix and unzip the two parental strands by breaking hydrogen bonds.

Helicase enzymes

The separated two parental strands act as ________.

templates

________ act as scaffolding, holding the two strands apart.

Single-stranded binding proteins

________ lessens the tension on the tight helix.

Topoisomerase

At each end of the replication bubble is a ________, a Y-shaped region where the new strands of DNA are elongating.

replication fork

________ cannot initiate the synthesis.

DNA polymerase III

The preexisting chain actually consists of ________ produced by an enzyme called primase.

RNA primer

As the two strands of DNA are ________, they are oriented in opposite directions to each other.

antiparallel

Explain why the formation of two new strands must be antiparallel to their template strands.

As the two strands of DNA are antiparallel, they are oriented in opposite directions to each other.

DNA polymerase can only add complementary nucleotides, C with G and A with T, to the free ________ end of the primer, never to the ________ end.

3':5'

Thus, a new DNA strand can elongate only in the ________ direction.

5' to 3'

________ replicates the two original strands differently.

DNA polymerase

Although it builds both new strands in the 5' to 3' direction, one strand is formed towards the replication fork in ________ fashion.

continuous and linear

This is called the ________.

leading strand

The other strand, the ________, forms in direction away from the replication fork, in a series of segments called Okazaki fragments.

lagging strand

Each Okazaki fragment is about ________ nucleotides long and then they are joined into one continuous strand by the enzyme DNA ligase.

100-200

________ carry out mismatch repair, a kind of proofreading that corrects errors.

DNA polymerase I

Damaged regions of DNA are excised out by ________.

DNA nuclease

Each time the DNA replicates, some ________ from the chromosome are lost.

nucleotides

To protect against the possible loss of genes at the end of the chromosomes, eukaryotes have special nonsense nucleotide sequences ________ at the ends of chromosomes that repeat thousands of times.

(TAAGGG)

These protective ends are called ________, which are created and controlled by the enzyme telomerase.

telomeres

So, every time DNA replicate, the ________ get shorter.

telomeres

________ is a set of rules for determining how genetic information in the form of a nucleotide sequence is converted to an amino acid sequence of a protein.

Genetic code

It defines a code specifying the relationship between a nucleotide codon and ________.

an amino acid

Researchers knew that there are only ________ nucleotides in RNA (A, U, G, and C), but 20 different kinds of amino acids.

four

Therefore, there could not be a ________ between nucleotides and amino acids.

one-to-one relationship

Explain why a two-nucleotide code is insufficient to code for 20 amino acids.

Even using two nucleotides per amino acid would only provide 4 × 4, or 16 possible combinations, which is not enough to code for 20 amino acids.

Thus, the minimum combination of the four nucleotides was a ________ code, which could produce 4 × 4 × 4, or 64 possible combinations.

triplet

From this reasoning came the ________, which proposed that the genetic code consists of a combination of three nucleotides, called a codon.

triplet hypothesis

Between 1961 and 1965, various research groups compared artificially synthesized RNA molecules of known nucleotide sequences with the ________ of polypeptides.

amino acid sequences

From these studies, the mRNA codons and their ________ were determined.

corresponding amino acids

By convention, the genetic code is always interpreted in terms of the ________ rather than the nucleotide sequence of the DNA.

mRNA codon

The genetic code has ________ important characteristics.

three

The genetic code is ________.

redundant

This means that more than one codon can code for ________.

the same amino acid

There are only ________ codons that do not code for any amino acid.

three

These codons serve as ________ to end protein synthesis.

“stop” signals

The genetic code is ________.

continuous

This means that it reads as a series of three-letter codons ________.

without spaces, punctuation, or overlap

Therefore, knowing exactly where to ________ protein synthesis is essential.

start and stop

A shift of one or two nucleotides in either direction can alter the ________ and result in an incorrect amino acid sequence.

codon groupings

The genetic code is ________.

nearly universal

Almost all organisms build ________ with the genetic code shown in Table 2.2.

proteins

The universality of the genetic code means that a codon in the fruit fly codes for ________ as in a human.

the same amino acid

This has important implications for ________, such as cloning.

gene technology

What will a gene that is taken from one kind of organism and inserted into another kind of organism produce?

The same protein.