MODULE NUCLEIC ACIDS

_____________ is an inherited disease which affects red blood cells.

sickle cell anemia

DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) belong to a class of

polymers called __________

nucleic acids

Like all other biomolecules, nucleic acids are made up of simple units. These simple units are called ___________

nucleotides.

Nucleic acids are therefore nucleotides joined or linked together. They may also be referred to as ____________

polynucleotides.

However, unlike other monomer units like amino acids of proteins and monosaccharides

of carbohydrates, nucleotides can be further __________ to three components:

hydrolyzed

The combination of sugar and nitrogenous base is called a ________

nucleoside.

There are two classes of nitrogen-containing bases found in nucleotides: _________ and

_______

• pyrimidines

• purines

__________ is present in both RNA and

DNA.

cytosine

________ is found only in nucleotides of DNA.

Thymine

______ replaces Thymine in RNA.

uracil

adenine and guanine are

purines

cystosine, thymine, and uracil are _________

pyrimidines

The second component of nucleotides is the _________,

pentose sugar

RNA contains the sugar ribose, and DNA contains a derivative of ribose, ___________

2 deoxyribose.

As a component of nucleic acids, the sugar units are in the ____________

beta furanose form.

It plays the important role of linking nucleotides together in the nucleic acid chain.

phosphoric acid

The phosphoric acid is joined to the sugar by an ____ linkage.

ester

The phosphoester is

analogous to the ester formed between____________ and alcohols.

carboxylic acids

A phosphoester linkage is possible where an ______ group exists in the sugar.

–OH

For both RNA and DNA, the nucleotide has phosphoric acid esterified to ___ of the

pentose sugar.

5’

Successive nucleotides are joined by ___________

phosphodiester linkages.

5' end has free _________ group

phosphate

3' end (with a free ________ group on the sugar).

hydroxyl

true or falsew: Some books use –ic acid to name a nucleotide.

true

Each human cell contains about __ meters of the nucleic acid DNA,

two meters

lenght of DNA molecules

200 micrometers

This reduction is possible because the DNA molecule wraps and folds itself around proteins, called ____________, which are tightly bound to the DNA.

histones

DNA was first isolated in ____, but the structure of the molecule was

not determined until 1953,

1868

The structure proposed by Watson and Crick consists of two helical polynucleotide chains coiled around the same axis, forming a _________

double helix

The _______________ sugar and phosphate components of the

nucleotides are found on the outside of helix

hydrophilic (water-loving)

the _________ bases are found on the inside.

hydrophobic

The nucleotides making up each strand of DNA are connected by ester bonds between the

phosphate group and the deoxyribose sugar as mentioned before. This forms the “_______” of

each DNA strand,

backbone

The bases of one strand of DNA will pair with

bases on the other strand by means of ___________

hydrogen bonding

As a result, the two strands of DNA are not identical, but

rather are __________

comlementary

The two chains or strands and also _________

antiparallel.

Aside from hydrogen bonding between complementary base pairs, ______________

contribute greatly to the stability of DNA.

hydrophobic interaction

The highly ____ sugar-phosphate backbone also shields the bases from water.

polar

The _________ model provides an explanation for the ability of

DNA to duplicate itself.

double helix model

The most important aspect of the DNA double helix is the _________ of the

pairing of bases.

specificity

They decided that adenine must pair with thymine and guanine with cytosine

because of s______ and ____________ factors

steric and hydrogen-bonding factors.

The unwinding of the double helix is called _______ because it

occurs abruptly at a certain temperature.

melting

It catalyzes the step-by-step addition of deoxyribonucleotide

units to a DNA chain.

DNA polymerase I

All four deoxyribonucleoside 5’-triphosphate – d ATP, dGTP, dTTP, and dCTP must be

present.

The abbreviation dNTP will be used to refer to these deoxyribonucleoside

triphosphates.

______ is also required.

Mg 2+

DNA polymerase 1 adds deoxyribonucleotides to the 3’-hydroxyl terminus of a pre-

existing DNA (or RNA) strand. In other words, a primer chain with a________ group is

required.

free 3’-OH

The template can be_____ or _____ stranded DNA.

single-or double

The chain-elongation reaction catalyzed by DNA polymerase occurs by means of a

___________ of the 3’-OH terminus of the primer on the innermost phosphorus atom of the

incoming deoxyribonucleoside triphosphate

nucleophilic attack

A phosphodiester bridge is formed and ____________ is concomitantly released.

pyrophosphate

The _________ of the DNA chain proceeds in the 5’ --→ 3’ direction.

elongation

DNA polymerase can hydrolyze DNA progressively from the 3’

– hydroxyl terminus of the DNA chain. The products are __________

mononucleotides.

5’ --→ 3’ nuclease activity is enhanced by concomitant ___________

DNA synthesis.

The nuclease activities of the DNA polymerase 1 functions in______________ during

polymerization.

editing nucleotides

• If there is a mistake or a mismatched residue at the primer terminus, it is usually

  removed before polymerization by the 3’ --- 5’ exonuclease.

• The 5’ --- 3’ exonuclease complements the 3’ --- 5’ exonuclease activity by correcting _______________

• errors of a different type,

This enzyme could catalyse the formation of a phosphodiester bond

between two DNA chains.

DNA ligase

The DNA ligase catalyzes the joining of two DNA chains that are ___ of a double-helical

molecule.

part

This enzyme requires a free OH group at the 3’ end of one DNA chain and a

phosphate group at the 5’ end of the other.

ligase Dna (this enzyme…)

DNA ligase, however, cannot link two molecules of

______________

single-stranded RNA.

Autoradiographic pattern indicates that replication is usually __________.

bidirectional

_________ strands are antiparallel

parental strands

Hence, the overall direction of DNA synthesis must be

5’ --- 3’ for one daughter strand and _________ for the other

3’ --- 5’ for the other.

TRUE OR FAKSE: all known DNA polymerase synthesize DNA in the 5’ --- 3’ direction, as well as in in the 3’ --- 5’ direction

FALSE, but not in the 3 →5

A large proportion of newly synthesized DNA exists as small fragments. These units of

about a thousand nucleotides (called _______________) are present momentarily in the

vicinity of replication fork.

Okazaki fragments

The strand formed from Okazaki fragments is termed the ____________

lagging strand,

the one synthesized with few or no interruptions is the __________

leading strand.

Molecule of RNA make up ____ of the total weight of the cell.

5-10%

The nucleotides of RNA contain ribose instead of deoxyribose, and the base ______ in place of ______.

uracil

thymine

it consists of a single strand of nucleic acid.

RNA

The additional hydroxyl group on the ribose is very important in forming hydrogen bonds that stabilize the___________ of the non-helical region of the RNA molecule.

tertiary structure

Francois Jacob and Jaques Monod proposed the name ____________ for that portion

of the total cell RNA carrying the genetic information from DNA to the ribosomes,

messenger RNA

messengers provide the templates for the biosynthesis of polypeptide chain with specific ____________________

amino

acid sequence.

mRNA is synthesized in the ______of the cell,

nucleus

mRNA is synthesized on _________ of a DNA helix, so it will have a sequence of bases

complementary to that of the DNA.

one strand

mRNA is not a _____molecule, and is synthesizd by the cell whenever it is needed

stable

After being synthesized, an mRNA molecule will migrate to the _________ of the animal cell. There it serves as a template or pattern for sequencing of amino acids in the synthesis of proteins in the ribosomes.

cytoplasm

_____ is also synthesized in the nucleus of the cell from a DNA template.

rRNA

rRNA migrates to the cytoplasm of the cell where, with ______, it forms the _______

• protein

• ribsomes

Ribosomes are the sites of protein synthesis, and are located on the _______________

endoplasmic reticulum.

The ribosomes are made up

of ___________ that combine with mRNA to form the “factory” for the production of protein.

two subunits

the smallest of the RNA molecules,

tRNA

tRNA is _________ and moves easily within the cell.

water-soluble

tRNA molecules are synthesized in the ___________, and each is specifically

designed for a particular amino acid.

nucleus of the cell

A tRNA molecule becomes charged when a specific amino

acid is joined to the ________________ present on each RNA polynucleotide chain.

terminal adenine nucleotide

_____ act by determining the kinds of protein made by cells.

genes

DNA is not the direct template for protein synthesis. Rather, the templates for protein synthesis are ________ molecules.

RNA (ribonucleic acid) - DNa is not…

The information is not transmitted directly to a protein synthesizing

system, but it is first transferred to RNA by the process of__________

transcription.

In this process, an RNA strand having a base sequence complementary to one of the DNA strands is synthesized by an ____________

enzyme system.

Transcription must be carried out _______ if the cell is to have proteins with

their normal genetically determined amino acid sequence.

faithfully

During replication the _____________ is copied to yield daughter DNAs identical to the parent DNA.

entire chromosome

But in the transcription process, not all of the cell DNA is necessarily transcribed. Only _____________ or ___________ are transcribed.

• individual genes\

• group of genes

Thus, the transcription of DNA is selective, turned on by ________________________________ indicating the beginning and end of the sequence of DNA to be transcribed.

specific

regulatory sequences

A group

of American biochemists were able to isolate such an enzyme which they called ____________________

DNA-directed

RNA polymerase.

RNA polymerase requires all four _______________ 5’-triphosphates (ATP, GTP, UTP, and CTP) as precursors of the

nucleotide units of RNA, as well as Mg 2+

ribonucleoside (RNA polyumers..)

___________ also take instruction from a DNA

template.

RNA polymerase

The RNA strand is _________by addition of ribonucleotide units to the 3’ hydroxyl end

of the RNA chain and builds the RNA chain in the 5’ --- 3’ direction

elongated

TRUE OR FALSE: Only one of the two DNA strands is transcribed.

TRUE (ONLY ONE…)

The new mRNA strand has also the ____________ to that of the

template strand.

polarity opposite

Although RNA polymerase does not require a primer strand, it cannot function

until it binds to a specific ___________ of the DNA template strand.

initiation signal

The enzyme then starts

the new RNA, at its 5’ end, usually with a _______or _______ residue, whose 5’ triphosphate group

designated ppp, is not cleaved to PPi, but remains intact throughout transcription.

GTP or ATP

During transcription, the new RNA strand base-pairs temporarily with the template DNA strand to form a short length of hybrid _______ double helix.

RNA-DNA

The hybrid duplex has only a ____________, since the RNA “peels off” shortly after its formation.

transitory existence

RNA polymerase is made up of sub-units. The subunit composition of the entire enzyme,

called a __________ in β β σ’.

haloenzyme