8a. Nucleic Acids

Question 1

What does DNA stand for

Answer 1

Deoxyribonucleic acid

Question 2

What does RNA stand for

Answer 2

Ribonucleic acid

Question 3

What are DNA and RNA

Answer 3

Important information-carrying molceules
Nucelic acids
Found in the nucleus and in the presenc of phosphate groups.
DNA ia the molecule that stores genetic info and RNA transfers it to ribosomes
Both made of nucleotides monomers

Question 4

What is a nucelotide made form

Answer 4

A pentose sugar
A nitro-organic base
A phosphate group

Question 5

How do nucleotides form polynucleotides

Answer 5

The phosphate group is linked to to the sugar on the next nucleotide by strong covalent Phosphodiester bonds
Creates the sugar-phosphate backbone
Condensation reaction

Question 6

What is a DNA nucleotide made up of

Answer 6

-Deoxyribose sugar
-N-Containing base: Adenine, Guanine, Cytosine or Thymine
-A phosphate group

Question 7

What are the catogrories of DNA bases

Answer 7

Purines ( Adenine and Guanine)
Pyrimidines ( Thymine and Cytosine)

Question 8

Are purines or pyrimidines longer

Answer 8

Purines a bigger than pyrimidines

Question 9

What is the sturcture of DNA

Answer 9

2 Polynucleotide chains
One running the opposite way to the other
Twist to form a double helix
Bases are held together by H bonding

Question 10

What is the term to discribe the pairing of bases

Answer 10

Complementary base pairing

Question 11

How many H bonds do each bases form in DNA

Answer 11

Aenine forms 2 with Thymine
Cytosine forms 3 with Guanine

Question 12

How does the structure of DNA relate to its function

Answer 12

-Stable molecule as its double helix with many H bonds
-Strong due to sugar-phosphate backbone
-Complementary base pairing allows DNA to replicate exactly
-Compact. Long so contain large amounts of coded information. Double helix allows it to fit in cell
-Precise genetic code determined by sequence of bases which control protein synthesis

Question 13

How many different amino acids are there in proteins

Answer 13

20

Question 14

What does RNA do

Answer 14

Transfers DNA from nucleus to cytoplasm.
Sections of DNA that code for polypeptides are copied onto a single standed molecule - RNA

Question 15

What is the structure of RNA

Answer 15

Relativley short, usually single stranded polynucleotides

Question 16

What is an RNA nucleotide made up of

Answer 16

-Ribose sugar
-N-containing organic base: Adenine, Guanine, Cytosine or Uracil
-A phosphate group

Question 17

What type of base is uracil

Answer 17

Pyrimidle

Question 18

What happens in semi-conservative replication

Answer 18

-DNA Helicase unwinds the DNA double helix by breaking weak H bonds between bases. This separates the strands
-Each exposed strand now acts as a template
-New DNA nucleotides from the nucleus are attracted to exposed bases and attach by complementary base pairing
-New H bonds form between bases
-DNA polymerase joins the adjacent nucleotides together by forming phosphodiester bonds via condenstation reactions

Question 19

Where does the name semi-conservative come from

Answer 19

Hlaf of the orginional DNA molecule is conserved in each new molecule

Question 20

What evidence is there for semi-conservative replication

Answer 20

In an experiment using E.Coli grown in a medium containing a heavy isotope.
Culture was then transffered to a medium containing normal light isotope
After time, samples taken and DNA extracted and centrifuged
With each successive generation the proportion of hybrid DNA halves and all the remaining DNA is ‘light’.

Question 21

What does ATP stand for

Answer 21

Adenosine triphosphate

Question 22

What is ATP

Answer 22

The immediate source of energy used by cells to drive their metabolic reactions

Question 23

What does an ATP molcules consist of

Answer 23

They are derived from nucleotides.
-Ribose sugar
-Organic base Adenine
-3 Phosphate groups (ions)

Question 24

How is ATP Synthesised

Answer 24

By the addition of ADP to an inorganic phosphate
Condensation reaction catalysed by ATP Synthase.
Addition of a phosphate molecule is Phosphorylation
Requires an input of energy from a metabolic process and occurs during respiration (or photosynthesis)

Question 25

Where is energy stored in an ATP molecule and how is ATP broken down

Answer 25

In the Phosphate-Phosphate bond between 2nd and 3rd phosphate Covalent link is unstable and easily broken by ATP Hydrolase in a hydrolysis reaction Inorganic phosphate group is removed, energy released ATP becomes ADP

Question 26

What is the role of ATP

Answer 26

Large number of roles in the metabolism of the cell Energy released when hydrolysed is used for active processes

Question 27

How is ATP used in Active transport

Answer 27

Required to move substances against a conc gradient using carrier proteins Protein pumps are also ATP hydrolase enzymes They catalyse the splitting of ATP to ADP and Pi Use the energy to change shape and pump the molecule

Question 28

How does exocytosis require ATP

Answer 28

To make vesicles which are synthesised by the Golgi body and package large molecules prior to secretion Energy also required for reverse process (endocytosis)

Question 29

How is ATP needed for the synthesis of substances (biosynthesis)

Answer 29

Required to make large molecules from smaller ones (monomers to polymers)

Question 30

How is ATP needed for movement

Answer 30

Energy required for muscle contraction

Question 31

How is ATP needed for activation of other molecules

Answer 31

ATP can transfer its phosphate group to other molecules, phosphorylating them and making them more reactive

Question 32

Whats ATP like as a source of energy

Answer 32

-Not a good long term energy store due to the instability of its phosphate bonds -Cells can maintain only a few seconds supply -Good immediate energy source, ATP is rapidly reformed from ADP and Pi. Reaction is reversible

Question 33

What is the ATP Cycle

Answer 33

ATP -- Hydrolysis --> ADP+Pi (+ energy released for use in cells) ADP + Pi --Condensation (+energy input) --> ATP

Question 34

Why is ATP more useful than glucose as an immediate energy source

Answer 34

-Breakdown of ATP to ADP is a single reaction, energy is immediatley avaliable. Breakdown of glucose is complex several stage reaction -ATP is soluble and easily moved around in cells but cant pass through membranes -Breakdown of ATP released a small amount of energy Breakdown of glucose release more energy than is required - inefficient as lots of energy would be wasted as heat