Nucleic acids

DNA and RNA are both types of what

nucleic acids

DNA and RNA are both important (-)-(-) molecules

important infomation carrying molecules

DNA holds (-) info found in all living cells

genetic infomation 0 the instructions an organism needs to grow and develop from a fertilised egg to a fully grown adult

DNA and RNA are ***** made from nucleotides 

polymers

what is the role of RNA

transfers genetic infomation from the DNA to the ribosomes. Ribosomes read the RNA to make polypeptides(proteins) in translation.

what are ribosomes made from

Ribosomes themselves are made from RNA and proteins

desribe the structure of a nucleotide

• pentose sugar- contains 5 carbons

• nitrogen-containing organic base 9organic means containing carbon) - contains carbon and nitrogen. thymine, guanine, adenenine, cytosine

• phosphate group- contains phosphate 

nucleotides are monomers and can join to form dimers (dinucleotides) andpolymers (polynucleotides)

draw a nucleotide

list the components of a RNA nucleotide 

1. Ribose - A pentose sugar.

2. A, U, G, or C base - Adenine, URACIL , guanine, or cytosine. 

3. A phosphate group

list the components of a DNA nucleotide

1. Deoxyribose - A pentose sugar.

2. A, T, G, or C base - Adenine, thymine, guanine, or cytosine.

3. A phosphate group

what type of bond is formed when nucleotides join together to form POLYNUCLEOTIDES (also name the reaction)

a phosphodiester bond is formed (consisting of a phosphate group and two ester bonds)

the nucleotides join by a condensation reaction between the phosphate group of one nucleotide and the sugar of another

what is the name of a chain of sugars and phosphates

sugar-phosphate backbone

describe the structure of DNA(strands, bonds between where?, direction of strands,carbons)

• two DNA polynucleotide strands would round each other to forma double helix 

• held by hydrogen bonds between complementry base pairs 

• the strands are antiparallel (opposite directions)

• one strand is 5’ to 3’ and the other is 3 to 5 (refers to the carbon number on the deoxyribose sugar 

name wich nitrogenous bases bond pair with eachother. what does this ensure

adenine-thymine

cystosine-guanine

• ensures accurate replication and stability of DNA as there are always equal ammounts of adenine and thymine in a DNA molecule and equal ammounts of cytosine and guanine 

how many hydrogen bonds form between A and T

2

how many hydrogen bonds form between C and G

3

how does the stucture relate to the function of DNA

• Stable due to the strong, covalent phosphodiester bonds in the sugar-phosphate backbone.

• Complementary base pairing allows for accurate replication.

• Hydrogen bonds between bases allow easy strand separation for replication and transcription.

• Compact structure fits inside the nucleus while storing a vast amount of genetic information​.

DNA is an important biological molecule. Describe its structure and explain how this structure allows it to carry out its function. (6 marks)

• DNA is a polymer of nucleotides.

• Each nucleotide contains a phosphate group, deoxyribose sugar, and a nitrogenous base 

• DNA is double-stranded and forms a double helix. This gives DNA a compact structure which fits inside the nucleus while storing a vast amount of genetic information​.

• The sugar-phosphate backbone is joined by phosphodiester bonds, giving DNA structural stability.

• Complementary base pairing occurs (A-T, C-G), which ensures accurate replication.

• The two strands run antiparallel (one runs 5’ to 3’, the other 3’ to 5’), allowing enzymes like DNA polymerase to function correctly.

• Hydrogen bonds between complementary bases allow strand separation, which is important for DNA replication and transcription.​

the relative simplicity of DNA led many scientists to doubt that it carried (-) (-)

genetic code

off spec but useful- what are purines and pyrimidines

• Purines - These are larger bases that contain two carbon ring structures (A and G).

• Pyrimidines - These are smaller bases that contain one carbon ring structure (T and C).

describe RNA stucture

a single stranded polynucleotide chain which is much shorter

uracil in RNA replaces what base in DNA

thymine

what type of replication does DNA undergo and what does mean and this ensure

semi-cnservative replication- meaning half the strands in each new DNA molecule are from the original DNA molecule.

This ensures genetic continuity between generations of cells (i.e the cells producedby cell divison inherit their genes from their parent cells

describe the process of semi-conservative DNA replication

• the double helix unwinds as DNA helicase causes strands to seperate/ breaks H- bonds between complementry base pairs

• Free nucleotides are attracted to exposed bases on template strands

• Complementry / specific base pairing

• DNA polymerase joins nucleotides together (on the new strans) by making phosphodiester bonds in condensation reactions

• the replication is semi conversative / new DNA molecules contain one old strand and one new strand

name the two enzymes involed in DNA replication and what they do

DNA helicase - breaks the hydrogen bonds between the complementry bases to seperate the two strands

DNA polymerase - joins adjacent nucleotides together by making PHOSPHODIESTER bonds in condensation reactions- this requires ATP

If an inhibitor of DNA polymerase were introduced into a cell, what would be the effect on cell division?

Cell division would stop as DNA replication cannot occur. 

This is because DNA polymerase cannot join nucleotides together and the new DNA strands will not form.

Why does DNA polymerase move in opposite directions along the two strands?

The two strands in DNA are antiparallel (they run in opposite directions). DNA polymerase is an enzyme with a specific tertiary structure and a specifically shaped active site. It can only attach new nucleotides at the 3’ end of a DNA nucleotide. This means it can only move in the 5’ to 3’ direction.

what did Watson and Crick discover

the double helix structure and the semi-conservative model of DNA replication which was validated by the Meselson and Stahl experiment

what is the conservative and fragmented or dispersive replication

conservative- one entirely new DNA molecule is amde, and the original remains intact

fragmented or dispersive - DNA strands are mixtures of old and new DNA 

Describe Meselson and Stahl’s experiment (1958)

context: bacteria will incorperate nitrogen into the bases in their DNA.
they used the bacterium E. coli and different isotopes of nitrogen to determine the correct model of DNA replication

1. Growing Bacteria in Heavy Nitrogen (15N):

   • E. coli was first grown in a medium containing only the heavy isotope of nitrogen (15N), which was incorporated into their DNA.

   • This made the DNA denser.

2. Switching to Light Nitrogen (14N):

   • The bacteria were then transferred to a medium containing only the lighter isotope of nitrogen (14N) and allowed to replicate once.

3. Centrifugation to Analyse DNA Density:

   • DNA was extracted and centrifuged to observe its position in the test tube.

   • It does this by spinning the extracted DNA at high speed. Causing the DNA to collect in different areas, depending on the density.

• After one round of replication in 14N:

  • DNA formed a single intermediate band in the centrifuge tube.

  • This disproved the conservative model, as there was no fully light (14N) or fully heavy (15N) DNA.

  • This supported the semi-conservative replication model, as the DNA consisted of one original (15N) strand and one newly synthesised (14N) strand.

  • After two rounds of replication in 14N:

    • Two distinct bands were observed

    • One intermediate density consisting of one original (15N) strand and one newly synthesised (14N) strand.

    • ​One less dense band that consisted of two strands containing 14N.

    • Final Conclusion:

      • The experiment provided strong evidence that DNA replication occurs via the semi-conservative model​.

  
  

how is ATP similar and different to RNA molecule

• They both contain ribose sugar.

• They both contain a nitrogenous base.

• They both contain a phosphate group.

• ATP always has the base adenine whereas RNA nucleotides can contain adenine, cytosine, guanine or uracil.

• ATP has 3 phosphate groups whereas RNA nucleotides have 1 phosphate group.

ATP is a ***** derivative

nucleotide

describe the structure of ATP

• Adenine – nitrogenous base.

• Ribose – a pentose sugar.

• Three phosphate groups – key to energy storage and release.