Nucleic Acids

Question 1

Types Of Nucleic Acids?

Answer 1

Ribonucleic Acid (RNA),
Deoxyribonucleic Acid (DNA).

Question 2

Nucleotide Structure?

Answer 2

Three basic components:

• Pentose sugar (made of 5 carbon atoms),
• Phosphate group,
• Nitrogen-containing organic base (C, T, U, A, G),

Pentose sugar, phosphate group and base join together because of condensation reactions to form a single mono-nucleotide,

Two mono-nucleotides join together because of a condensation reaction between the deoxyribose sugar of one mono-nucleotide and a phosphate group of another mono-nucleotide.

Question 3

Bond Between Two Mono-Nucleotide?

Answer 3

Is called a phosphodiester bond,

This new structure of the two mono-nucleotides is called a dinucleotide,

If the dinuclotide link continues, the link is called a polynucleotide.

Question 4

Symbols?

Answer 4

Other molecules that contain nucleotides are represented by symbols:

Phosphate - circle,
Pentose sugar - pentagon (5 sides),
Adenine - rectangle with triangle cut on one side (flag),
Guanine - same as above but with half-circle cut,
Cytosine - same as above but with half-circle add-on,
Thymine - same as adenine but with the triangle cut added on,
Uracil - same as thymine (above).

Question 5

Nitrogen-Containing Organic Base Names?

Answer 5

C - cytosine,
T - thymine,
U - uracil,
A - adenine,
G - guanine.

Question 6

Ribonucleic Acid Structure?

Answer 6

Is a polymer made of nucleotides,

It’s a single, relatively short nucleotide chain in which the pentose sugar is always RIBOSE,

The organic base is always ADENINE, GUANINE, CYTOSINE and URACIL,

One type of RNA transfers genetic information from DNA to ribosomes,

The ribosomes themselves are made of proteins and another type of RNA,

A third type of RNA is involved in protein synthesis.

Question 7

DNA Structure?

Answer 7

The pentose sugar is always DEOXYRIBOSE,

The organic base is always ADENINE, THYMINE, GUANINE and CYTOSINE,

Made of two strands of nucleotides (polynucleotides),

Each of the strands is extremely long and joined together by hydrogen bonds formed between certain bases,

Phosphate and deoxyribose alternate to form the uprights,

Organic bases pair together to form the rungs.

Question 8

Who Discovered DNA Structure?

Answer 8

1953 - James Watson and Francis Crick worked out the structure of DNA,

This followed the work by Rosalind Franklin on the X-ray diffraction patterns of DNA.

Question 9

Base Pairing?

Answer 9

Bases on the two strands attach by hydrogen bonds,

A - - - T,
G - - - C,

The bases are completely to each other,

Quantities of C and G in DNA are always the same and the quantities of A and T are the same,

However, the ratio of all four of the bases are not always the same, e.g. A is not always the same as C,

The ratio of this depends on the species.

Question 10

How Many Hydrogen Bonds Between Bases In DNA?

Answer 10

3 bonds between G and C,

2 bonds between A and T.

Question 11

DNA Is Stable Because?

Answer 11

The phosphodiester backbone protects the more chemically reactive organic bases inside the double helix,

Hydrogen bonds link the organic base pairs forming bridges (rungs) between the phosphodiester uprights. As there are three hydrogen bonds between C as G pairings, the higher the proportion of C-G pairs, the more stable the DNA molecule,

There are other interactive forces between the base pairs that hold the molecule together (base stacking).

Question 12

DNA Variety?

Answer 12

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

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

This vast number means that there is an most infinite variety of sequences of bases along the length of a DNA molecule,

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

Question 13

Adaptions Of DNA?

Answer 13

Certain adaptions allow DNA to function,

• It is a stable structure which passes from generation to generation without change normally. Only rarely does it mutate,
• It’s two separate strands are joined by hydrogen bonds which allow them to separate during DNA replication and protein synthesis,
• Extremely large molecule and therefore carries an immense amount of genetic information,
• By having the base pairs within the helical cylinder of the deoxyribose backbone, the genetic information is to some extent protected from being corrupted by outside the chemical and physical forces,
• Base pairing leads to DNA being able to replicate and to transfer information as mRNA.

Question 14

Cell Division?

Answer 14

Cells that make up organisms are always derived from existing cells by the process of division,

Cell division occurs in two ways:

• Nuclear division,
• Cytokinesis,

Before a nucleus divides, its DNA must be replicated (copied). This is to ensure that all the daughter cells have the genetic information to produce the enzymes and other proteins they need,

DNA replication is precise because all the cells are pretty much identical to original one. The semi-conservative model is universally accepted.

Question 15

Nuclear Division?

Answer 15

Type of call division,

Process by which the nucleus divides,

There are two types of nuclear division (mitosis and meiosis).

Question 16

Cytokinesis?

Answer 16

Type of cell division and is the process by which the whole cell divides.

Question 17

Requirements Of Semi-Conservative Replication?

Answer 17

Four requirements for semi-conservative replication to take place:

• Four types of nucleotide, each with their bases of A, T, C and G must be present,
• Both strands of DNA act as a template for the attachment of these nucleotides,
• Enzyme DNA polymerase must be present,
• A source of chemical energy is required.

Question 18

Process Of Semi-Conservative Replication?

Answer 18

• DNA helicase breaks the hydrogen bonds linking the base pairs of DNA,
• As a result, the double helix separated into two strands and unwinds,
• Each exposes polynucleotide strand then acts as a template to which complementary, free nucleotides bind by specific base pairing,
• Nucleotides are joined together in a condensation reaction by the enzyme DNA polymerase to form another polynucleotide strand on each of the original polynucleotide strands,
• Each of the new DNA molecules contains one of the original DNA strands and a new DNA strand. This process is termed ‘semi-conservative replication’.

Question 19

Semi-Conservative Replication Evidence Based On What Facts?

Answer 19

Meselsohn and Stahl’s experiment was based on three facts:

• All the bases in DNA contain nitrogen,
• Nitrogen has two forms - lighter nitrogen (14n) and the isotope (15n), which is heavier,
• Bacteria will incorporate nitrogen from their growing medium into any new DNA that they make.

Question 20

The Conservative Model?

Answer 20

A suggested model for DNA replication,

Suggested that the orbital DNA molecule remained intact g and that a separate daughter DNA copy was built up from new molecules of deoxyribose, phosphate and organic bases,

Of the two molecules produced, one would be made of new material and one would be old material.

Question 21

The Semi-Conservative Model?

Answer 21

A suggested type of DNA replication,

Proposed that the original DNA molecule split into two separate strands, each of which then replicated its mirror imagine,

Each of the two new molecules contained one strand of new material and one strand of old material.

Question 22

Semi-Conservative Replication Evidence?

Answer 22

They reasoned that bacteria grown on a medium containing 14n would have DNA that was lighter than bacteria grown on a medium containing 15n,

They labelled the original DNA of bacteria by growing them on a medium of 15n,

They then transferred the bacteria to a medium of 14n for a single generation to allow it to replicate once,

The mass of each ‘new’ DNA molecule would depend upon which method of replication had taken place,

To separate out the different DNA types, they centrifuged the extracted DNA in a special solution,

The lighter the DNA, the nearer the top of the centrifuge type it collected,

The heavier the DNA, the nearer the bottom of the tube,

They also analysed the DJA after two, then three, generations,

By interpreting the results they could determine which hypnosis I was correct.

Question 23

ATP Name?

Answer 23

Adenosine Triphosphate.

Question 24

Structure Of ATP?

Answer 24

Consists of three parts:

• Adenine (a nitrogen-containing organic base),
• Ribose (a sugar molecule with a 5-carbon ring structure - pentose sugar - that acts as the backbone to which the other parts are attached),
• Phosphates - a chain of three phosphate groups.

Question 25

How Does ATP Store Energy?

Answer 25

ATP is a nucleotide and has three phosphate groups (as name suggests - triphosphate), The bonds between these phosphate groups are unstable and so have a low activation energy, which means they are easily broken, When they do break, they release a considerable amount of energy, Usually in living cells it is only the terminal phosphate that is removed, according to the equation.

Question 26

ATP Break And Release Energy Equation?

Answer 26

ATP + H2O —> ADP + Pi + E, ADP - adenosine diphosphate, Pi - inorganic phosphate, E - energy, Only terminal phosphate is removed, As water is used to convert ATP to ADP, this is known as a hydrolysis reaction. The reaction is catalysed by the enzyme ATP HYDROLASE (ATPase).

Question 27

Synthesis Of ATP?

Answer 27

ATP to ADP is a reversible reaction. And therefore energy can be used to add inorganic if phosphate to ADP to re-form ATP according to the equation. ADP + Pi —condensation reaction—> ATP This is catalysed by ATP synthase and uses energy to occur. ATP —hydrolysis reaction—> ADP + Pi This is catalysed by ATP hydrolyse and energy is released. ADP has 2 phosphate groups, and ATP has 2. Pi = inorganic phosphate.

Question 28

Synthesis Of ATP Process?

Answer 28

Synthesis of ATP to ADP involves the addition of a phosphate molecule to ADP. It occurs in three ways: - In chlorophyll-containing planet cells during photosynthesis (photophosphorylation), - In plant and animal cells during respiration (oxidative phosphorylation), - In plant and animal cells when phosphate groups are transferred from donor molecules to ADP (substrate-level phosphorylation).

Question 29

Downsides Of ATP?

Answer 29

The instability of the phosphate bonds make ATP a good energy donor, however, this also makes them a bad long term energy store, Fats and carbohydrates are better for this (such as glycogen), ATP is therefore an immediate energy source, As a result, cells do not store large quantities of ATP, but rather just maintain a few seconds supply, This is not an issue as ATP is rapidly re-formed from ADP and Pi and so a little goes a long way, ATP cannot be stored.

Question 30

ATP Is A Better Immediate Energy Source Because?

Answer 30

- Each ATP molecule releases less energy than each glucose molecule. The energy for reactions is therefore released in smaller, more manageable quantities rather than less manageable energy from a glucose molecule, - The hydrolysis of ATP to ADP is a single reaction that releases immediate energy. The breakdown of glucose is a long series of reactions and therefore the energy release takes longer.

Question 31

ATP Uses In Cells Such As?

Answer 31

Metabolic Processes - provides energy needed to build up macromolecules from basic units. E.g. making starch from glucose or polypeptides from amino acids, Active Transport - provides energy to change the shape of carrier proteins in plasma membranes. Allows molecules or ions to be moved against a concentration gradient, Movement - provides energy for muscle contraction; energy for the filaments of muscles to slide past one another and Theodore shorten the overall length of a muscle fibre, Secretion - needed to form the lysosomes necessary for the secretion of cell products, Activation Of Molecules - inorganic phosphate released during hydrolysis of ATP can be used to phosphorylate other compounds in order to make them more reactive, thus lowering the activation energy in enzyme-catalysed reaction. E.g. the addition of phosphate to glucose molecules at the start of glycolysis.

Question 32

Water Is Bipolar?

Answer 32

Hydrogen has a + charge and oxygen has a - charge, However, the whole molecule has no overlap charge, The molecule is said to be bipolar.

Question 33

Water And Hydrogen Bonding?

Answer 33

Different poles attract, The + of the water will attract to - of another water, This force is a hydrogen bond, Each bond is fairly weak, (1/10 of a covalent), Together, they make the water molecules stick together, This gives water it’s unusual properties.

Question 34

Specific Heat Capacity Of Water?

Answer 34

Water molecules stick together, therefore, it takes more energy (heat) to separate them, Water acts as a buffer against sudden temperature variations, making the aquatic environment a temperature stable one.

Question 35

Latent Heat Of Vaporisation Of Water?

Answer 35

Hydrogen bonding means that it requires a lot of energy to evaporate 1 gram of water, This energy is called the latent heat of vaporisation, Evaporation of water such as west in mammals is therefore a very effective means of cooling because body heat is used to evaporate the water.

Question 36

Cohesion And Surface Tension In Water?

Answer 36

The tendency of molecules to stick together is knows as cohesion, With hydrogen bonding, water has large cohesive forces and this allows it to be pulled through a tube, such as a xylem vessel in plants, In the same way, where water molecules meet air they tend to be pulled back into the body of water rather than escaping from it, This force is called SURFACE TENSION and means that the water surface acts like a skin and is strong enough to support small organisms such as pond skaters.

Question 37

Water In Metabolism?

Answer 37

Water is used to break down many molecules by hydrolysis, e.g. proteins to amino acids, Water is produced in condensation reactions, Chemical reactions take place in an aqueous medium, Water is a major raw material in photosynthesis.

Question 38

Water As A Solvent?

Answer 38

Water readily dissolved other substances: - Gases such as oxygen and carbon dioxide, - Wastes such as ammonia and urea, - Inorganic ions and small hydrophilic molecules such as amino acids, monosaccharides and ATP, - Enzymes, whose reactions take place in solution.

Question 39

Other Important Features Of Water?

Answer 39

Waters evaporation cools organisms down and allows control of temperature, Not easily compressed and therefore provides support, e.g. hydrostatic skeleton of animals such as the earthworm and turgid pressure in herbaceous plants, Transparent and therefore aquatic plants can photosynthesise and also light rags can penetrate the jelly-like fluid that filled the eye and so reach the retina.

Question 40

Inorganic Ions?

Answer 40

Found in organisms where they occur in solution in the cytoplasm of called and in body fluid, May be in concentrations that range from very high to very low, Perform a range of functions, The specific function a particular ion performs is related to its properties, e.g. iron ions are found in haemoglobin where they play a role in transport of oxygen. Other examples include phosphate ions that form a structural role in DNA and in storing energy in ATP molecules. Hydrogen ions are important in determining the pH of solutions, therefore, functioning enzymes.

Question 41

Inorganic ions have an electric charge?

Answer 41

A ion is an atom or group of atoms that has an electric charge. An ion with a positive charge is cation, anion has a negative charge. An ion organic ion is one which doesn’t contain carbon (there’s a few exceptions to this rule). There are inorganic ions, in solution, in the cytoplasm of cells and in the bodily fluids of organisms. Each ions has a specific role, depending on it properties. An ions role is determined whether it’s sound in high or low concentration.

Question 42

Iron ions?

Answer 42

Haemoglobin is a large protein that carries oxygen around the body, in red blood cells. It’s made of four different polypeptide chains and each chain has a iron ion (Fe2+) in the centre. It’s the ion that binds to the oxygen in haemoglobin. When oxygen is bound, the Fe2+ ion is temporarily a Fe3+ ion until the oxygen is released.

Question 43

Hydrogen ions?

Answer 43

pH is calculated based on concentration of H+ ions in the environment. The more H+, the lower the pH (and more acidic the environment). Enzyme controlled reactions are all affected by pH.

Question 44

Sodium ions?

Answer 44

Na+. Glucose and amino acids need help crossing cell membranes. A molecule of glucose of an amino acid can be transported into a cell (across cell-surface membrane) alongside sodium ions (Na+). This is co-transport.

Question 45

Phosphate ions?

Answer 45

PO4^3-. When a phosphate ions is attached to another molecule, it is known as a phosphate group. DNA, RNA and ATP all contain phosphate groups. It’s the bonds between phosphate groups that stop energy in ATP. The phosphate groups in DNA and RNA allow nucleotides to join up to form polynucleotides.