2.1.3 - Nucleotides and Nucleic Acids

Question 1

What is a nucleotide made of

Answer 1

Pentose monosaccharide
Phosphate Group PO4 2-
Nitrogenous base

Question 2

Phosphodiester bonds

Answer 2

Formed in a condensation reaction between nucleotides
Phosphate group at 5’ forms covalent bond with hydroxyl group 3’ (H2O)
Forms a long, strong sugar-phosphate backbone with a base attached to each sugar

Question 3

Difference between ribose and deoxyribose

Answer 3

Deoxyribose doesn’t have an oxygen atom at 2’

Question 4

Bases

Answer 4

Adenine
Cytosine
Guanine
Thymine/ uracil

Question 5

Pyrimidines

Answer 5

Smaller bases
Single carbon ring structures
Thymine/ Cytosine

Question 6

Purine

Answer 6

Larger bases
Double carbon ring structures
Adenine/ Guanine

Question 7

How do bases pair up

Answer 7

A purine with a pyramidine
Cytosine pairs with guanine - 3 H bonds
Adenine pairs with thymine (uracil - RNA) - 2 H bonds

Question 8

Structure of DNA

Answer 8

Hydrogen bonding between complementary bases
Double helix composed of two twisted antiparallel strands (phosphate group 5’ - OH 3’/ OH 3’ - phosphate group 5’)
Each strand is a polynucleotide

Question 9

Why are polynucleotide chains parallel

Answer 9

Complementary base pairing rule:
When a small pyramidine base binds to a larger purine base a constant distance between the DNA ‘backbones’

There will also always be equal amounts of A, T, C, G

Question 10

Types of RNA

Answer 10

Messenger RNA (mRNA)
Transfer RNA (tRNA) 
Ribosomal RNA (rRNA)

Question 11

mRNA

Answer 11

Carries the code held in the genes to the ribosomes where the code is used to manufacture proteins

Question 12

tRNA

Answer 12

Transports amino acids to the ribosomes

Question 13

rRNA

Answer 13

Makes up the ribosomes along w/ protein complexes

Question 14

Phosophorylated nucleotides

Answer 14

ADP and ATP
Contain a pentose sugar (ribose)
A nitrogenous base (adenine)
2/ 3 inorganic phosphates

Question 15

Semi conservative replication

Answer 15

One old strand and one new strand

Question 16

Process of semi-conservation replication

Answer 16

Helicase causes the DNA to untwist and breaks the hydrogen bonds between bases
Polynucleotides with exposed bases act as new template for new double strands
Free DNA nucleotide bases pair with their complementary bases - H bonds
DNA polymerase catalyses the formation of phosphodiester bonds between the nucleotides and also checks base pairing
Sugar phosphate backbone reforms
Each new molecule then twists to form it’s double helix

Question 17

Purpose of DNA replication

Answer 17

Genetic info needs to be conserved with accuracy so each cell from cell division has the correct amount of genes

Question 18

Continuous replication

Answer 18

DNA polymerase binds to the end of a strand
Free DNA nucleotides added without any breaks
This occurs in the leading strand (3’ to 5’)

Question 19

Discontinuous replication

Answer 19

DNA polymerase cannot bind to the end of a strand (5’- 3’)
Free DNA nucleotides are added in sections (Okazaki fragments)
Sections are later joined by DNA ligase

Question 20

Mutations

Answer 20

Incorrect sequences may occur in the newly-copied strand
Errors happen randomly and spontaneously
Leads to change in the sequence of bases

Question 21

Codon

Answer 21

Triplet of bases that code for an amino acid

Question 22

Genetic code

Answer 22

Triplet code

Question 23

Genetic code is universal

Answer 23

All organisms use this same code

Question 24

Degenerate code

Answer 24

64 different codons possible (444) but only 20 amino acids
An amino acid can be coded for by more than one codon

Question 25

Non-overlapping

Answer 25

DNA base sequence is read from base 1 not base 2 or 3

Question 26

Nature of genetic code

Answer 26

Triplet code Non-overlapping Degenerate Universal

Question 27

Synthesis of polypeptide

Answer 27

Transcription | Translation

Question 28

Transcription

Answer 28

Conversion of the genetic code to a sequence of nucleotides in mRNA Reading the code and producing a messenger molecule to carry the code out to the cytoplasm

Question 29

Translation

Answer 29

Converting the code in mRNA to a sequence of amino acids

Question 30

Gene

Answer 30

A length of DNA that codes for one polypeptide

Question 31

Start codon

Answer 31

Signals the start of a sequence that codes for a protein

Question 32

Stop codons

Answer 32

There are 3 codons that do not code for any amino acids and signal the end of a sequence

Question 33

Process of transcription

Answer 33

DNA strands separate (same process as replication) Sense strand contains code for protein (5’ to 3’) Free RNA nucleotides base pair to complementary bases exposed on antisense/ template strand (3’ to 5’) - used to build copy of coding strand RNA polymerase joins bases to form single-strand RNA (phosphodiester bonds) mRNA detaches from DNA template and strands reform helix. mRNA leaves through nuclear pores and enters cytoplasm

Question 34

Process of translation

Answer 34

mRNA enters ribosomal groove and binds to small subunit in ribosomes tRNA molecule carrying amino acid binds to mRNA start codon and another binds to next mRNA codon with complementary anti codons (max. 2) - these form H bonds Peptidyl transferase causes a peptide bond to form between amino acids Ribosome moves along mRNA, releasing first tRNA Process stops when ribosome reaches end of mRNA with stop codon and detaches

Question 35

Conservative model

Answer 35

Proposed that that the original DNA served as a complete template so that the resulting DNA was completely new

Question 36

Dispersive model

Answer 36

Proposed that the two new DNA molecules had part new and part old DNA interspersed throughout them

Question 37

Transcription unit

Answer 37

Comprises of at least one gene but often more

Question 38

mRNA vs complementary DNA sequence

Answer 38

They’re the same but T is replaced by U

Question 39

How many base pairs are there in one full turn of the DNA double helix

Answer 39

10

Question 40

Why is the double helix structure of DNA important

Answer 40

Keep DNA stable Enables it to fit much info in a small space Protects bases in the middle

Question 41

Role of DNA ligase

Answer 41

Joins sugar-phosphate backbone of DNA Catalyses formation of phosphodiester bonds Joins promoter to gene and promoter and gene to plasmids

Question 42

How is the replication fork formed

Answer 42

When the helicase starts to break H bonds between the bases on the two antiparallel strands

Question 43

Okazaki fragments

Answer 43

Short single stranded DNA molecule complementary to DNA on lagging strand

Question 44

Do start codons code for an amino acid

Answer 44

Yes only stop codons do not

Question 45

DNA polymerase

Answer 45

Reads in the 3' to 5' direction and builds in the 5' to 3' direction

Question 46

DNA extraction procedure

Answer 46

Grind sample in pestle and mortar - break cell wall Add detergent - breaks down csm Add salt - breaks H bonds between DNA and water Add protease - breaks down histones Add ethanol - causes DNA to ppt out of sol to be collected using a glass rod

Question 47

What types of activity does the cell require energy for

Answer 47

Synthesis e.g protein Transport Movement - sliding filament model

Question 48

What makes ATP a good immediate energy store

Answer 48

The interconversion of ATP and ADP is constantly happening so not much ATP is required

Question 49

Properties of ATP

Answer 49

Small - moves easily in and out of cells Water-soluble - energy requiring processes happen in aq Easily regenerated Releases energy is small quantities - energy not wasted as heat Contains bonds between phosphates w/ intermediate energy - large enough to meet needs of cellular reactions