chapter 2 - nucleic acids

Question 1

What does DNA do ?

Answer 1

• codes for the sequence amino acids in the primary structure of a proteins
• which determines the final 3D structure of a protein

Question 2

What are the monomers that make up DNA called ?

Answer 2

• nucleotides

Question 3

What are DNA nucleotides made up of

Answer 3

• a deoxyribose pentose sugar
• a nitrogenous base : A,T,C or G
• a phosphate group

Question 4

What are the 4 nitrogenous bases ?

Answer 4

• adenine, thymine, guanine and cytosine

Question 5

How are polynucleotides formed ?

Answer 5

• bonds forms between the phosphate group of one nucleotide and the deoxyribose sugar of another nucleotide
• by condensation reactions
• these forms phosphodiester bonds

Question 6

What properties do phosphodiester bonds that makes them suitable for holding nucleotides ?

Answer 6

• they are strong covalent bonds
• which ensure the genetic code doesn’t break down
• they help to hold the sugar phosphate backbone which is strong

Question 7

What holds DNA strands together ?

Answer 7

• hydrogen bonds
• which can only form between the complementary bases pairs

Question 8

How many hydrogen bonds form between the 2 complementary bases pairs ?

Answer 8

• 2 bonds between adenine and thymine
• 3 bonds between cytosine and guanine

Question 9

Why is the complementary base pairing in DNA important ?

Answer 9

• it helps maintain to maintain the genetic code when the DNA replicates

Question 10

How does the structure of DNA relate to its function ?

Answer 10

• sugar phosphate backbone and double helix = stable structure, protects bases
• double strand = one strand can used be as a template in replication
• weak hydrogen bonds = can easily be unzipped during replication
• large molecule = can carry a lot of info
• complementary bases paring = identical copies can be made and reduces copying errors which could lead to mutations
• double helix = molecules is compact

Question 11

What are purines an pyrimidines ?

Answer 11

• purines = larger bases with 2 carbon ring structures: adenine and guanine
• pyrimidines = smaller bases than have 1 carbons ring structures: thymine and cytosine

Question 12

What is RNA and what is its function ?

Answer 12

• a short polynucleotide made from RNA nucleotides
• used to copy and transfer genetic codes from DNA in the nucleus to ribosomes to make proteins
• can also be combines with proteins to make ribosomes

Question 13

What are RNA nucleotides made of

Answer 13

• a ribose pentose sugar
• a nitrogenous base : A,C,G or U
• a phosphate group

Question 14

What are the three types of RNA ?

Answer 14

• mRNA
• tRNA
• rRNA

Question 15

Describe mRNA

Answer 15

• messenger RNA
• a copy of one gene from the DNA
• leaves the nucleus to carry the genetic code to the ribosomes in the cytoplasm

Question 16

Describe tRNA

Answer 16

• transfer RNA
• folded in a clover leaf shape held by hydrogen bonds
• only found in cytoplasm
• its job is to transfer amino acids to the ribosome
• specific amino acids attach to specific tRNAA molecules

Question 17

Describe rRNA

Answer 17

• ribosomal RNA
• combines with proteins to make up most of the ribosomes

Question 18

What are the differences between DNA and RNA ?

Answer 18

For monomer differences :
- DNA has thymine whilst RNA has uracil
- DNA contains deoxyribose pentose sugar whilst RNA has ribose pentose sugar
For polymer differences :
- DNA is much larger with thousands of genes, RNA is shorter as its only one gene
- DNA is double stranded, RNA is single stranded

Question 19

What happens in semi conservative replication ?

Answer 19

• the DNA molecule produce will have one original parental strand and one newly synthesised daughter strand

Question 20

What 2 enzymes are involved in semi conservative replication ?

Answer 20

• DNA helicase
• DNA polymerase

Question 21

How does semi conservative DNA replication work

Answer 21

• DNA helicase breaks the hydrogen bonds between the complementary base pairs which separates the 2 strands
• each strand acts as a template to allow free nucleotides to attract to their complementary base pairs
• DNA polymerase joins (catalyses) adjacent nucleotides by condensation reactions in the 5’ to 3’ direction
• this forms phosphodiester bonds to make the sugar phosphate back bone of the daughter DNA strand
• 2 sets of daughter DNA are formed
• now there are two identical copies of DNA , each with one parental strand and one newly synthesised strand

Question 22

What makes up ATP ?

Answer 22

• adenine tripohosphate
• adenine = nitrogenous base
• ribose - pentose sugar
• 3 inorganic phosphate groups

Question 23

What is the function of ATP ?

Answer 23

• to act as an immediate source if energy for biological processes

Question 24

How does ATP release energy

Answer 24

• ATP is hydrolysed (water is added) to make ADP + Pi
• this releases energy
• uses ATP hydrolase enzyme

Question 25

How is ATP created ?

Answer 25

• condensation reaction between Pi and ATP
• releases water
• requires energy
• happens during respiration

Question 26

What is ATP used for in the body ?

Answer 26

• movement
• active transport
• synthesis of large molecules like DNA and proteins
• secretion of substances from cells

Question 27

How do the properties of ATP make it good for its function ?

Answer 27

• hydrolysis of ATP releases small amounts of energy which mean less energy is wasted
• its small and soluble so can be transported outside of the cell
• only one bond hydrolysed in ATP ( only takes one step ), glucose has many bonds, so energy release is quick/immediate
• can transfer energy to other molecules through phosphorylation = when the inorganic phosphate binds to another molecule to make it more reactive
• ATP cannot pass out of the call, glucose can, so a cell will always have a constant supply of ATP
• ATP is rapidly re synthesised so ATP is always available