nucleic acids + DNA replication Flashcards
biological molecules
describe the basic functions of DNA and RNA in all living cells
-DNA: holds genetic information which codes for polypeptides (proteins)
- RNA: transfers genetic information from DNA to ribosomes
name the two types of molecules from which a ribosome is made from
- RNA
- proteins
what are DNA composed of?
a double stranded helix structure, containing a sugar phosphate backbone with a nitrogen-containing organic base pairs in the centre
what are the structures of a nucleotide?
- a strand of DNA or RNA is a polynucleotide made up from joined mononucleotide
- individual nucleotides are made from 3 components
1. phosphate group
2. a pentose sugar (deoxyribose/ribose)
3.an organic base - the phosphate group and the pentose sugar are the back bones
- organic base contains nitrogen
DNA is made from which monomer?
mononucleotides
Identify the molecule.
ribose
diagram of a DNA nucleotide
diagram of a RNA nucleotide
describe the differences between a DNA and a RNA nucleotide
- in DNA the pentose sugar is deoxyribose whereas its ribose in RNA
- in DNA the base contains thymine whereas in RNA its uracil instead
describe how nucleotides join together to form polynucleotides
-condensation reaction, removing water molecules
-between phosphate group of one nucleotide and deoxyribose/ribose of another
-forming phosphodiester bonds
why did many scientists initially doubt that DNA carried the genetic code?
the relative simplicity of DNA- chemically simple molecule with few components
in DNA what is adenine complementary to?
Thymine
in DNA what is cytosine complementary to?
guanine
in RNA what is adenine complementary to?
uracil
in RNA what is cytosine complementary to?
guanine
describe the structure of DNA
● Polymer of nucleotides (polynucleotide)
● Each nucleotide formed from deoxyribose, a phosphate group and a
nitrogen-containing organic base
● Phosphodiester bonds join adjacent nucleotides
● 2 polynucleotide chains held together by
hydrogen bonds
● Between specific complementary base
pairs - adenine / thymine and cytosine / guanine
● Double helix
describe the structure of (messenger) RNA
● Polymer of nucleotides (polynucleotide)
● Each nucleotide formed from ribose, a phosphate
group and a nitrogen-containing organic base
● Bases - uracil, adenine, cytosine, guanine
● Phosphodiester bonds join adjacent nucleotides
● Single helix
compare and contrast the structure of DNA and RNA
how is DNA a stable molecule?
- the phosphodiester backbone protects the more chemically reactive bases inside the double helix
-C-G base pairs contain 3 hydrogen bonds, so the more C-G base pairs in a DNA molecule the more stable it is.
-there are interactive forces between base pairs that holds the molecules together. This is called ‘base stacking’. This makes the molecules more stable
Suggest how the structure of DNA relates to its functions
- has a phosphodiester backbone : prevents organic bases reacting with environment
- long molecule : store lots of genetic information (that codes for polypeptides)
3.double helix structure (coiled) : makes DNA compact
4.Hydrogen bonds between bases are weak → strands can be separated for replication
5.Two strands → both can act as templates for semi-conservative replication
6.Complementary base pairing (base sequence) → accurate replication, information can be stored and codes for amino acids/proteins
7.Many hydrogen bonds between bases → stable / strong molecule
8.base stacking : makes DNA stable
How many hydrogen bonds are formed between Cytosine and Guanine in a DNA molecule?
3
Name the bond that forms between the 2 nucleotides of a dinucleotide.
phosphodiester bond
How is DNA adapted to carry out its function as a means of passing genetic information from generation to generation?
-Very stable - rarely mutates
-Hydrogen bonds between strands easy to separate for replication and protein synthesis.
-Very long - carries a lot of genetic information.
-Base pairs protected from chemical/physical forces by phosphodiester backbone.
Name the 3 Scientists who discovered the structure of DNA
-James Watson
-Francis Crick
-Rosalind Franklin
How many hydrogen bonds are formed between Adenine and Thymine in a DNA molecule?
2
How are the 2 strands of DNA that make up the double helix held together?
Hydrogen bonds between complementary organic bases
Identify the molecule
phosphoric acid (phosphate)
The phosphate group attaches to which carbon atom of a ribose or deoxyribose molecule when forming a nucleotide?
The 5’ carbon atom (pronounced 5 prime)
Identify the molecule
deoxyribose
Suggest how you can use incomplete information about the frequency of
bases on DNA strands to find the frequency of other bases
- % of adenine in strand 1 = % of thymine in strand 2 (and vice versa)
- % of guanine in strand 1 = % of cytosine in strand 2 (and vice versa)
Because of specific complementary base pairing between 2 strands
If 19.9% of the base pairs in human DNA are guanine, calculate the percentage that is Thymine. Show your reasoning.
30.1%
If 19.9% is guanine - 19.9% is cytosine as it is paired with it.
19.9 + 19.9 = 39.8%.
The remaining DNA is made from Adenine and Thymine, which is 60.2%. Thymine = 60.2% divided by 2 = 30.1%.
How do the organic bases help to stabilise structure of DNA?
-Hydrogen bonds between the base pairs holds two strands together;
-Many hydrogen bonds provides strength;
Why is semi-conservative replication important?
Ensures genetic continuity between generations of cells
Describe the process of semi-conservative DNA replication
- DNA helicase breaks hydrogen bonds between complementary bases, unwinding the double helix
- Both strands act as templates
- Free DNA nucleotides attracted to exposed bases and join by specific complementary base pairing
- Hydrogen bonds form between adenine-thymine and guanine-cytosine
- DNA polymerase joins adjacent nucleotides on new strand by condensation reactions
- Forming phosphodiester bonds
define Semi-conservative
each new DNA molecule consists of one original / template strand and one new strand
what 4 things are needed during DNA replication?
-DNA molecule to be replicated
-free DNA nucleotides
-DNA helicase enzymes
-DNA polymerase
suggest why DNA polymerase moves in opposite directions along DNA strands
● DNA has antiparallel strands
● So shapes / arrangements of nucleotides on two ends are different
● DNA polymerase is an enzyme with a specific shaped active site
● So can only bind to substrate with complementary shape (phosphate end of developing strand)
Describe the work of Meselson and Stahl in validating the Watson-Crick model of semi-conservative DNA replication
- Bacteria grown in medium containing heavy nitrogen (
15N) so
nitrogen is incorporated into DNA bases
○ DNA extracted & centrifuged → settles near bottom, as all
DNA molecules contain 2 ‘heavy’ strands
2. Bacteria transferred to medium containing light nitrogen (14N) and allowed to divide once
○ DNA extracted & centrifuged → settles in middle, as all DNA
molecules contain 1 original ‘heavy’ and 1 new ‘light’ strand
3. Bacteria in light nitrogen (14N) allowed to divide again
○ DNA extracted & centrifuged → half settles in middle, as
contains 1 original ‘heavy’ and 1 new ‘light’ strand; half settles
near top, as contains 2 ‘light’ strands
Function of DNA helicase?
break H bonds between bases
Function of DNA polymerase?
join adjacent nucleotides together forming phosphodiester bonds
true or false “DNA polymerase forms phosphodiester
bonds between bases.”
false.
DNA polymerase forms phosphodiester bonds between the
phosphate group of one nucleotide & the deoxyribose of another.
true or false “Free bases attach to exposed bases.”
false.
Free nucleotides attach to exposed nucleotide bases via complementary base pairing, but not the bases on their own.
