Eduqas Biology A Level Core Concepts - Nucleic Acids and their functions (includes ATP)

Nucleic acid definition

A polymer of nucleotides

What are DNA and RNA examples of?

nucleic acids

What does DNA stand for?

deoxyribonucleic acid

What does RNA stand for?

ribonucleic acid

What is ATP an example of?

A nucleotide

Why is ATP considered a nucleotide and not a nucleic acid?⁶

It is one singular molecule, whereas nucleic acids are polymers

What does ATP stand for?

adenosine triphosphate

Nucleotide definition

The basic unit (monomer) from which nucleic acids are formed

What are the 3 main components of a nucleotide?

phosphate group, sugar, and an organic nitrogenous base

Draw a simple nucleotide, showing the sections clearly with labels

What is special about the sugar in all nucleotides?

It is always a pentose (5 carbons)

What is the pentose sugar in DNA?

deoxyribose

What is the pentose sugar in RNA?

ribose

What is the pentose sugar in ATP?

Ribose

How many different nitrogenous bases are there?

5

What nitrogenous base does ATP contain?

Adenine

Why is ATP considered the universal energy currency?

Because it is used in all energy-requiring reactions in all cells in all living organisms

Draw an ATP molecule and label its parts.

What reactions is ATP used in?

- Active transport

- Protein synthesis

- Nerve transmission

- Muscle contraction

How is ATP formed?

By adding a phosphate group to ADP (phosphorylation of ADP)

What kind of reaction is the combination of ADP and a phosphate group?

condensation

What kind of reaction is the formation of ADP and a phosphate group from ATP?

hydrolysis

How much energy is realised by the hydrolysis of ATP?

30.6kJ

What are two groups of nitrogenous bases?

Pyrimidine and purine

What are the 5 kinds of nitrogenous bases?

Adenine, cytosine, guanine, thymine and uracil

How would you differentiate between a pyrimidine base and a purine base?

Pyrimidine bases are single ringed, purine bases are double ringed

What are the pyrimidine bases?

Cytosine, thymine, uracil

What are the purine bases?

Adenine and guanine

What bases does DNA contain?

Adenine, Thymine, Guanine, Cytosine

What bases does RNA contain?

Adenine, Guanine, Cytosine, Uracil

Describe the structure of DNA

DNA is made up of two strands of nucleotides wound into a double helix, with a sugar-phosphate backbone and inner facing bases

What forms the backbone of a DNA strand?

sugar and phosphate

What bonds form between the sugar and the phosphate group of adjacent nucleotides in a DNA molecule?

covalent

What holds the two strands of DNA together?

hydrogen bonding between complimentary base pairs

What kind of bond forms between complimentary base pairs in DNA?

hydrogen bonds

What base does the base adenine pair with in DNA?

Thymine

What base does the base thymine pair with in DNA?

Adenine

What base does the base cytosine pair with in DNA?

Guanine

What base does the base guanine pair with in DNA?

Cytosine

How many hydrogen bonds are between adenine and thymine?

2

How many hydrogen bonds are between cytosine and guanine

3

If 20% of the bases in DNA are adenine, what is the % of each of the other bases?

Thymine = 20%

Guanine = 30%

Cytosine = 30%

What are the 3 types of RNA?

Messenger RNA (mRNA)

Ribosomal RNA (rRNA)

Transfer RNA (tRNA)

What is the purpose of mRNA?

To carry genetic information from the DNA to the ribosomes for protein synthesis

What is the purpose of rRNA?

It combines with proteins to make ribosomes

What is the purpose of tRNA?

Transports amino acids to the ribosome for translation

Where is mRNA formed?

nucleus

Genetic code defintion

The way in which information about the sequence of amino acids in a protein is coded by the bases on a molecule of DNA

Describe the process of DNA replication

- A DNA molecule is unwound and the hydrogen bond between complimentary base pairs are broken by the enzyme DNA helicase

- Each separated single strand of DNA now acts as a template, and free DNA nucleotides will line up against complimentary base pairs on the template strand

- DNA polymerase catalyses the combination of adjacent free DNA nucleotides, creating a new chain

- A new DNA molecule has been formed, made from one parent strand and one newly synthesised chain

What is DNA helicase and what does it do?

An enzyme that unwinds and unzips the double helix

What is DNA polymerase and what does it do?

DNA polymerase is an enzyme that joins individual nucleotides to produce a new strand of DNA

What is the structure of mRNA?

Single, uncoiled strand

What is the structure of rRNA?

globular

What is the structure of tRNA?

cloverleaf shaped, with one arm carrying the anticodon

What are the two functions of DNA?

replication and protein synthesis

What are the names of the 3 theories of DNA replication?

conservative replication, semi-conservative replication and dispersive replication

Draw a diagram to show conservative replication of DNA

Draw a diagram to show semi-conservative replication of DNA

Draw a diagram to show dispersive replication of DNA

What is conservative replication of DNA?

The parental DNA molecule remains intact, and a completely new DNA molecule is synthesised

What is semi-conservative replication of DNA?

The parental double helix splits, each acting as a template for two new strands. Both new DNA molecules contain 1 parent strand and 1 newly synthesised strand

What is dispersive replication of DNA?

The two new double helices contain fragments from both strands of the parental DNA strand, as well as newly synthesised fragements

Describe the Meselson-Stahl experiment

- They grew bacterium with the heavy isotope of nitrogen, so the isotope was incorporated into the DNA (centrifuged sample produces a low band)

- The bacteria is then placed in the light isotope of nitrogen and allowed to replicate once (produces a band in the middle)

- In the same isotope, the bacteria are allowed to replicate again (produces one band in the middle and one band at the bottom)

What theory of DNA replication does the Meselson-Stahl experiment support?

semi-conservative

Define gene

A section of DNA on a chromosome which codes for a specific polypeptide

What is a codon?

A three-nucleotide sequence that codes for an amino acid

Why is the genetic code described as degenerate?

More than one codon can represent one amino acid

Define genetic code

The DNA and mRNA base sequences that determine the amino acid sequences in an organism's proteins

What is a stop codon?

A codon that signals the end of translation

Define Exon

coding regions of DNA and RNA (included in mRNA)

Define Intron

non-coding sequences of DNA and pre-mRNA (not included in mRNA)

What is removed and what is kept when pre-mRNA is changed into mRNA?

Introns are removed, Exons are kept

Define transcription

The process of copying the genetic code from DNA into the form of mRNA

Define translation

Assembling a protein using the message carried by mRNA

Describe the process of transcription

- DNA unwinds and separates using DNA Helicase, making two separate template strands

- Free RNA nucleotides align with template strand through complimentary base pairing

- RNA polymerase bonds the nucleotides together, forming a molecule of mRNA complimentary to the DNA

- mRNA leaves nucleus via nuclear pores

Describe the process of translation

- mRNA attaches to the ribosome and translation begins with the start codon

- A tRNA molecule with an anti-codon complimentary to the start codon lines up against the mRNA strand

- A second tRNA molecule lines up adjacent to the first

- The adjacent amino acids on each tRNA molecules form peptide bonds with the aid of an enzyme

- The first tRNA molecule detaches and new tRNA molecule joins, lengthening the polypeptide chain

- This carries on until a stop codon is reached

- The both the mRNA molecule and the newly synthesised polypeptide chain leave the ribosome

The conversion of ATP into ADP is a _______ reaction and ______ energy

hydrolysis, releases

The conversion of ADP into ATP is a _______ reaction and ______ energy

condensation, uses/requires

What makes ATP a better supplier of energy than glucose?

- For ATP, it is a single step reaction whereas for glucose there are many steps

- ATP gives out a manageable release of energy, unlike glucose with its sudden, explosive release

- Only one enzyme is required for ATP, but glucose requires more

- ATP is a smaller molecule so is easier to transport than glucose

In what nucleic acids is Uracil found?

RNA only

In what nucleic acids is Thymine found?

DNA only

DNA helicase is important in DNA replication. Explain why

- DNA helicase unwinds the DNA double helix and separates the two strands

- So that free DNA nucleotides can attach and a new strand can be made

Describe the role of DNA polymerase in DNA replication

It joins nucleotides together and forms the sugar-phosphate backbone

Other than being smaller, give two ways in which prokaryotic DNA is different from eukaryotic DNA

- It doesn't form chromosomes

- It is circular

- It contains no introns

When analysing the DNA of a virus, it was found that the percentages of each base are as follows:

Adenine = 24.0%

Guanine = 23.3%

Thymine = 21.5%

Cytosine = 31.2%

Suggest what this may indicate about viral DNA

- The complimentary base pairs do not share the same percentage (A does not equal T, G does not equal C)

- This tells us there is no base pairing involved

- Therefore the viral DNA is most likely single stranded

Which molecule is know as the 'universal energy carrier'?

ATP

Which components of a DNA molecules form its backbone?

Deoxyribose sugar and phosphate

groups

What is the mechanism of DNA replication known as?

semi-conservative replication

Why is semi-conservative replication called what it is?

Each new DNA molecule produced contains one original parental strand and one newly synthesised strand

Name the bond formed between the bases on a DNA helix

hydrogen bond

Explain what is meant by the term 'triplet code'

A sequence of 3 bases to form an amino acid

What is the difference between an intron and an exon?

- Introns are a non-coding nucleotide

sequence in DNA that is removed before mRNA is formed

- Exons are a nucleotide sequence that

remains present

What is the one gene-one polypeptide hypothesis and what knowledge does it give us about DNA

and protein synthesis?

- A theory which suggests that a particular sequence of DNA bases must be

entirely present to code for a polypeptide, in order to create the right protein

- This tells us that if

there is damage/mutation to any section of the DNA, certain important proteins such as

enzymes/antibodies/hormones/structural and transport proteins etc. will not be available for key

functions

Summarise what happens in Post-translational modification?

In the Golgi Body; where a polypeptide is needed to be folded into secondary, tertiary or quaternary structures; and may be chemically modified (adding carbohydrates etc)

Translate the DNA sequence of bases to an mRNA molecule copy: TACGGGCATTTCAACGTA

How many amino acids does this code for?

AUGCCCGUAAAGUUGCAU

6 amino acids

Describe the function of tRNA

- To provide the anticodon sequences for coding information

- To provide specific amino acid to be added to a polypeptide chain

Explain the importance of the anticodon on a tRNA molecule

Each anticodon is specific to one amino acid only

Explain what ensures that the correct amino acid is added to a growing polypeptide chain during translation

- Each tRNA molecules has an anticodon which is specific to an amino acid

- The anticodon matches to one specific codon on the mRNA molecule

It is important that translation is carried out correctly. Explain why

A small mistake in the order of amino acids will cause the shape of the final protein to change when it is folded. The protein will only perform its function if the structure is correctly reproduced

A bacteria was grown for many generations in a medium containing the heavy isotope of nitrogen, N¹⁵

The cells were then transferred to a medium containing normal nitrogen, N¹⁴, and allowed to divide once.

Explain why the density of the DNA of these cells in the new generation was intermediate between that of normal nitrogen and those cultured in the heavy nitrogen medium

DNA replicates via semi-conservative replication. The newly synthesised DNA contains one strand from the parent DNA, containing the N¹⁵ isotope, as well as one new strand containing the N¹⁴ isotope.