Nucleic Acid and their functions

Question 1

Components of a nucleotide

Answer 1

Phosphate, Pentose sugar, Nitrogenous base

Question 2

Example of a nucleotide

Answer 2

ATP - major currency of the cell
adenine, rubose, phosphate

Question 3

How is energy released in ATP ?

Answer 3

• The enzyme ATPase breaks the bonds between the middle and terminal phosphate group
• Adenosine diphosphate and a phosphate group is formed too

Question 4

2 types of Nucleic Acid

Answer 4

• DNA ( deoxyribonucleic acid )
• RNA ( Ribonucleic acid)

Question 5

ATP uses

Answer 5

• Metabollic Processes = build large, complex molecules from from smaller, simpler molecules
• Active Transport
• Movement
• Nerve Transmission = Sodium - potassium pumps actively transport sodium and potassium ions across the axon cell membrane
• Secretion

Question 6

DNA Nucleotide structure

Answer 6

• Pentose sugar, Deoxyribose
• Bases = Adenine, Thymine Cytosine or Guanine

Question 7

RNA Nucleotide structure

Answer 7

• Phophaste chain
• Ribose
• Bases = Adenine, uracil, Cytosine, Guanine

Question 8

mRNA

Answer 8

• long single-stranded molecule and just long enough to contain 1 gene (about 1000 nucleotides)
• Short life time and degrades shortly after being used
• ## Manufactured in the nucleus and carries the genetic code from the DNA to the ribosomes in the cytoplasm

Question 9

Ribosomal RNA

Answer 9

• rRNA is found in the cytoplasm and is a made up of both double and single helices
• Ribosomes are made up of rRNA and protein
• Ribosomes the site of protein synthesis by a process called translation

Question 10

Transfer RNA (tRNA)

Answer 10

• small single stranded molecule in the shape of a clover leaf
• It is an ‘adapter’ that matches amino acids to their codons and brings amino acids to the ribosomes so protein can be synthesised
• At one end of the molecule is always the base sequence C-C-A, where the amino acids bind
• on the middle loop there is a triplet nucleotide sequence/ the anticodon
• 64 different tRNA molecules each with a different anticodon sequence coplimentary to the 64 different codons

Question 11

Conservative Replication of DNA

Answer 11

• Parental double helix remains intact and a new helix is made

Question 12

Semi-conservative DNA replication

Answer 12

Parental Double helix separates into 2 strands each acting as a template for new strands

Question 13

Dispersive DNA replication

Answer 13

• the two new double strands contain fragments from both strands of the parental helix

Question 14

Meselson and Stahl

Answer 14

-Proposed the semi-conservative idea
- Cultered the bacterium escherichia coli for several generations on a medium containing amino acids made with heavy isoptope 15N
- The bacteria incorporated the 15N into their nucleotide and after 7 generations DNA contained all 15N

Question 15

Meselson and Stahl experiment explanation

Answer 15

-The scientists extracted the bacterial DNA and centrifuged it.
The DNA settled at a low point in the tube because it contained the heavy 15N isotope
- The bacteria were washed, then transferred to a medium containing the normal lighter isotope 14N and were allowed to replicate once.
When extracts of DNA from the first generation culture were centrifuged it was shown to have a mid-point density
(positioned in the middle of the tube); half the strand was made up of 15N DNA and the other half was made up of new
14N DNA

• When extracts of DNA were taken from the second generation grown in a 14N medium the DNA settled at mid-points and
  high-points in the tube after centrifugation

This provided evidence which supported the semi-conservative hypothesis.

Question 16

Translation

Answer 16

• Ribosomes act as framwork moving along the mRNA, reading the code
• mRNA contains triplet codes or codons. Each codes for a different amino acid
• tRNAread the codon and get the anitcodon with specific amino acid on the top of it and carrys it to the mRNA moleucle
• Complimentary codon- anticodon bases align. Codon-anticodon complex formed
• Peptide bonds are formed between adjacent amino acids by codensation reaction

Question 17

How are all types of RNA involved in protein synthesis ?

Answer 17

• messenger RNA (mRNA) is a long single-stranded molecule formed into a helix. It
  is manufactured in the nucleus and carries the genetic code from the DNA to the
  ribosomes in the cytoplasm.
• ribosomal RNA (rRNA) is found in the cytoplasm and is a large, complex molecule
  made up of both double and single helices. Ribosomes are made up of ribosomal
  RNA and protein.
• transfer RNA (tRNA) is a small single stranded molecule. It forms a clover-leaf
  shape, with one end of the chain ending in a cytosine-cytosine-adenine sequence at
  which point the amino acid it carries attaches itself. At the opposite end of the
  chain is a sequence of three bases called the anticodon. tRNA molecules bring
  amino acids to the ribosome so that proteins can be synthesised.

Question 18

Transcription

Answer 18

• DNA helicase breaks hydrogen bonds between the bases in the helix,
  unwinding the DNA, exposing unpaired bases
• RNA polymerase links to the template strand of DNA adding mRNA
  nucleotides one at a time, complementary base pairing and forming phosphodiester bonds between them.
  RNA polymerase continues until the STOP codon and then leaves DNA. The molecule is called pre- mRNA as it contains both exons and introns.
• After the RNA polymerase the DNA strand re-join to reform the double helix.
• Post- transcriptional modification of pre-mRNA then occurs to remove the
  introns from the molecule to produce functional mRNA.
• The mRNA carries DNA code out of the nucleus through a nuclear pore to
  the cytoplasm and attaches itself to a ribosome.

Question 19

Differences between DNA and RNA

Answer 19

DNA
-Deoxyribose sugar
- Uracil is absent (thymine)
- Double stranded molecule, run anti-parallel
- Mostly present in nucleus and mitochondria
- Bases are not modified

RNA
- Ribose sugar
- Thymine absent (Uracil)
- Single stranded molecule
- Present in nucleolus and cytoplasm
- Bases are modified w

Question 20

DNA Replication

Answer 20

• DNA Helicase breaks Hydrogen bonds between the bases, DNA unwinds into two separate strands.
• Enzyme DNA polymerase catalyses the addition of free nucleotides to the exposed bases (forming phosphodiester bonds).
• Each chain acts as a template so that free nucleotides can be joined to their complimentary bases.
• Results in the formation of two identical DNA molecules; each made
  up of one newly synthesised strand and one parent strand from the original molecule.

Question 21

The Genetic Code

Answer 21

• The sequence of nucleotide bases forms a code. Each “code word” has three letters called a triplet code / Codon, these code for a specific amino acid.
• More than one triplet can encode each amino acid, so the code is described as “degenerate” or “redundant”.
• One codon acts as a START codon, marking the point on the DNA where Transcription begins
• Each gene found on the DNA will code for a different polypeptide: this is called the one gene, one polypeptide hypothesis.

Question 22

Roles of a nucleotide

Answer 22

• Building blocks of nucleic acid
• Regulatory chemicals
• Formation of energy carries (ADP, ATP)
• Formation of coenzymes

Question 23

One gene – One polypeptide hypothesis

Answer 23

one gene – one polypeptide hypothesis- Each time a ribosome moves along a mRNA
molecule a polypeptide molecule is produced. The polypeptide (primary protein structure)
can be modified, folded, and combined with other polypeptides to form secondary, tertiary
and quaternary protein structures. One gene codes for a single polypeptide.

e.g the quaternary protein haemoglobin has four different polypeptide chains, therefore
four genes are needed to code for haemoglobin.