answer and question 2.1.2 to 2,2

What is RNA like compared to DNA?

Like DNA, RNA is a polymer of nucleotides.

What bases does RNA contain?

RNA contains four nucleotides with the bases adenine (A), uracil (U), cytosine (C), and guanine (G).

How does RNA differ from DNA in terms of strands?

Unlike DNA, RNA is single-stranded.

What stabilizes the looped structure of tRNA?

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

Where are RNA molecules synthesized?

Since all are produced from a DNA template, all are synthesized in the nucleus.

How many different RNA molecules involved in protein synthesis are listed in Table 2.1?

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

What is the hereditary material responsible for passing genetic information from cell to cell and generation to generation?

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

Approximately how many base pairs are in the DNA of a typical mammalian cell?

In total, there are around 3.2 billion base pairs in the DNA of a typical mammalian cell.

What does the vast number of base pairs in DNA mean?

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

What provides the genetic diversity within living organisms?

It is this variety that provides the genetic diversity within living organisms.

Is the DNA molecule adapted to carry out its functions?

The DNA molecule is adapted to carry out its functions in a number of ways.

Describe the stability of the DNA structure.

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

How often does the DNA structure mutate?

Only rarely does it mutate.

What joins the two separate strands of DNA and what does this allow?

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

Why does DNA carry a large amount of genetic information?

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

How is the genetic information within the structure protected from being corrupted?

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

What does base pairing lead to?

Base pairing leads to DNA being able to replicate and to transfer information to mRNA.

What does the function of DNA depend on?

The function of the remarkable molecule, DNA depends on the sequence of base pairs that it possesses.

Why is the sequence of base pairs important?

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

What is DNA replication?

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

What method is DNA replication made by and who predicted it?

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

Explain why DNA replication is regarded as semiconservative.

It is regarded as semiconservative because each of the resulting two molecules consists of one old strand and one new strand.

What assists in the replication of DNA?

Proteins and enzymes assist in replication of DNA.

Where does DNA replication begin?

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

What do helicase enzymes do?

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

What do the separated two parental strands act as?

The separated two parental strands act as templates.

What is the function of single-stranded binding proteins?

Single-stranded binding proteins act as scaffolding, holding the two strands apart.

What is the role of topoisomerase?

Topoisomerase lessens the tension on the tight helix.

What is a replication fork?

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

Can DNA polymerase III initiate the synthesis?

DNA polymerase III cannot initiate the synthesis.

What does the preexisting chain actually consist of?

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

In what directions are the two strands of DNA oriented?

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

How must the formation of two new strands be relative to their template strands?

Therefore, the formation of two new strands must also be antiparallel to their template strands.

To which end of the primer can DNA polymerase add complementary nucleotides?

DNA polymerase can only add complementary nucleotides, C with G and A with T, to the free 3' end of the primer, never to the 5' end.

In which direction can a new DNA strand elongate?

Thus, a new DNA strand can elongate only in the 5' to 3' direction.

Does DNA polymerase replicate the two original strands the same way?

DNA polymerase replicates the two original strands differently.

How is one strand formed towards the replication fork?

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

What is the strand formed continuously towards the replication fork called?

This is called the leading strand.

How does the lagging strand form?

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

How long is each Okazaki fragment and what joins them together?

Each Okazaki fragment is about 100-200 nucleotides long and then they are joined into one continuous strand by the enzyme DNA ligase.

What enzyme carries out mismatch repair?

DNA polymerase I carry out mismatch repair, a kind of proofreading that corrects errors.

How are damaged regions of DNA excised?

Damaged regions of DNA are excised out by DNA nuclease.

What happens to nucleotides from the chromosome each time DNA replicates?

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

What special sequences do eukaryotes have at the ends of chromosomes to protect against the loss of genes?

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

What are these protective ends called and what controls them?

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

What happens to telomeres every time DNA replicates?

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

What is the genetic code?

Genetic code 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.

What does the genetic code define?

It defines a code specifying the relationship between a nucleotide codon and an amino acid.

How many nucleotides are in RNA and how many kinds of amino acids are there?

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

Why could there not be a one-to-one relationship between nucleotides and amino acids?

Therefore, there could not be a one-to-one relationship between nucleotides and amino acids.

Why is a two-nucleotide code 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.

What was the minimum combination of the four nucleotides?

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

What did the triplet hypothesis propose?

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

What did research groups compare between 1961 and 1965?

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

What were determined from these studies?

From these studies, the mRNA codons and their corresponding amino acids were determined.

How is the genetic code always interpreted by convention?

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

How many important characteristics does the genetic code have?

The genetic code has three important characteristics.

What is the first characteristic of the genetic code?

The genetic code is redundant.

What does the redundancy of the genetic code mean?

This means that more than one codon can code for the same amino acid.

How many codons do not code for any amino acid?

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

What do the three non-coding codons serve as?

These codons serve as “stop” signals to end protein synthesis.

What is the second characteristic of the genetic code?

The genetic code is continuous.

How is the genetic code read?

This means that it reads as a series of three-letter codons without spaces, punctuation, or overlap.

Why is it essential to know exactly where to start and stop protein synthesis?

Therefore, knowing exactly where to start and stop protein synthesis is essential.

What can result in an incorrect amino acid sequence?

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

What is the third characteristic of the genetic code?

The genetic code is nearly universal.

What do almost all organisms build proteins with?

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

What does the universality of the genetic code mean practically?

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

What does the universality of the genetic code have implications for?

This has important implications for gene technology, such as cloning.

What will a gene produce if it is taken from one organism and inserted into another?

A gene that is taken from one kind of organism and inserted into another kind of organism will produce the same protein.