DNA and RNA

Question 1

how does DNA replication occur

Answer 1

The enzyme, DNA helicase, causes the DNA double helix to unwind and separate into two strands by breaking the hydrogen bonds between complementary base pairs, exposing the bases.
Both separate strands then act as a template for DNA replication to occur.
Free activated DNA nucleotides (in the nucleoplasm) are attracted to and hydrogen bond to their complementary bases on the exposed template strands by complementary base pairing.
The newly added nucleotides are then joined together by the enzyme DNA polymerase, which catalyses the formation of phosphodiester bonds, between adjacent nucleotides.
This results in two identical DNA molecules being produced, each of which contains one of the original DNA strands and one newly synthesised DNA strand (semi-conservative).

Question 2

What does every nucleic acid contain

Answer 2

Phosphate group
Penrose sugar
Nitrogenous base

Question 3

How are DNA strands held together

Answer 3

Complementary base pairing
Hydrogen bonds between them
Adenine-Thymine 2 hydrogen bonds
Thymine-uracil 2 hydrogen bonds
Cytosine-guanine 3 hydrogen bonds

Question 4

Which nitrogenous bases form the most hydrogen bonds between their complementary base pairs

Answer 4

Adenine-Thymine 2 hydrogen bonds
Thymine-uracil 2 hydrogen bonds
Cytosine-guanine 3 hydrogen bonds

Question 5

How is DNA adapted to its function

Answer 5

-stable structure allowing to pass from generation to generation
-Two strands held together by weak Hydrogen bonds, easy to unwind
-complementary base pairs so accurate replication
-large molecule

Question 6

Describe DNA structure

Answer 6

-double helix
-contains two polynucleotide chains
-extremely long
-always deoxyribose sugar
-bases ATCG

Question 7

What are the bases for DNA

Answer 7

Adenine
Thymine
Cytosine
Guanine

Question 8

What is the structure of RNA

Answer 8

-single stranded
-short polynucleotide chain
-always ribose as the Penrose sugar
Based AGCU

Question 9

What are the bases for RNA

Answer 9

adenine
Guanine
Cytosine
Uracil

Question 10

Why is DNA stable

Answer 10

-the sugar phosphate backbone protects the bases inside the double helix
-many hydrogen bonds are strong together

Question 11

What is ATP made up of

Answer 11

Adenine
Ribose
3 phosphate

Question 12

What is the role of ATP

Answer 12

• metabolic processes
  -active transport
  -movement
  -energy requiring reactions in cells

Question 13

How is ATP created

Answer 13

ADP + inorganic phosphate + ATP synthase

Question 14

What are the properties of ATP

Answer 14

-releases energy in small manageable amounts
-one single bond broken, immediate energy store
-provides energy for undertones reactions
-readily available
-water soluble
Cannot cross plasma membrane so stays in cell

Question 15

What is cell fractionation

Answer 15

The process where cells are broken up (lysed) and the different organelles within are separated out

Question 16

Before undergoing cell fractionation what should the conditions be

Answer 16

Cold
Buffered
Isotonic

Question 17

Why should it be cold before cell fractionation

Answer 17

To reduce enzyme activity that could break down the organelles

Question 18

Why should it be buffered before cell fractionation

Answer 18

So that PH doesn’t affect organelles and proteins

Question 19

Why should it be isotonic before cell fractionation

Answer 19

To prevent organelles from bursting or shrinking as a result of osmotic water loss

Question 20

What are the stages of cell fractionation

Answer 20

Homogenisation.
Filtration
Ultracentrifugation

Question 21

What is homogenisation

Answer 21

This breaks open the cells. This is done by either vibrating the cells or vrinding them up in a homogeniser

Question 22

What is filtration

Answer 22

The resulting fluid (homogenate) is filtered through filter paper to remove any non homogenised tissue

Question 23

What is ultracentrifugation

Answer 23

The fragments are separated by repeated centrifugation at higher speeds
Produces pellet and supernatant
The pellet is the densest part of the cell. For example the first pellet is the nucleus