Nucleic acids

What are nucleic acids and examples?

Large biological molecules (polymers) made of nucleotide monomers

Examples are DNA and RNA

What are nucleic acids made of?

Carbon, hydrogen, oxygen, nitrogen and phosphorous

What are 3 components that make up a nucleotide?

A Pentose monosaccharide (sugar) containing 5 carbon atoms

A phosphate group

A nitrogenous base

How do the nitrogenous bases pair?

A-T. And C-G The bases pair with complementary bases via hydrogen bonds

How do nucleotides join together to form nucleic acids?

By condensation reactions to form a polymer called polynucleotide

What is a phosphodiester bond?

A covalent bond that joins 2 nucleotides together

How does a phosphodiester bond form and what does it form between?

Formed by a condensation reaction Forms between the phosphate group on carbon 5 (5') of one nucleotide and the OH group of carbon 3 (3') on the next nucleotide.

How are phosphodiester bonds broken?

Hydrolysis which releases the individual nucleotides

What is the sugar-phosphate backbone?

The repeating phosphate and sugar joined by phosphodiester bonds Adds strength and stability to the nucleic acid molecule

What is the sugar group in DNA called?

Deoxyribose

Why is is called deoxyribose?

Because it has 1 fewer oxygen atoms than ribose

How many nitrogenous bases does DNA have and what are they called?

4 ATCG

What are the 2 groups that the bases are split into called?

Pyramidines and purines

They pair with each other

What are Pyramidines?

Smaller Contain a single carbon ring structure Consist of Thymine and cytosine (TC) and uracil in rna

What are purines?

Larger

Contains double carbon ring structure

Consists of Adenine and Guanine (AG)

How many hydrogen bonds do Adenine and Thymine form?

2

How many hydrogen bonds do cytosine and guanine form?

3

What word is used to describe the 2 strands of DNA?

the two strands of DNA are antiparallel

What is complementary base pairing?

The specific pairing of nitrogenous bases in nucleic acids

A smaller pyramidine always binds to a larger purine How does this affect the DNA molecule?

This arrangement maintains a constant distance between the DNA backbones resulting in parallel polynucleotide chains

What does complementary base pairing mean for the DNA molecule?

It always has equal amounts of adenine and thymine+ also equal amounts of cytosine and guanine

What is RNA?

A single stranded nucleic acid made of nucleotide monomers containing ribose sugar as the sugar group.

What is Thymine replaced with in RNA?

Uracil

What bonds joins up nucleotides in RNA (and DNA)?

Phosphodiester bonds

What is mRNA?

messenger RNA

How is mRNA formed?

During the transcription from the template DNA strand

What does mRNA carry with it?

The genetic code/codons for specific amino acids Each codon codes for a specific amino acid

What is tRNA?

Transfer RNA

What does tRNA do?

Brings specific amino acids, each tRNA having an anticodon complementary to an mRNA codon.
Hydrogen bonds for between codon and anticodon (base pairing)
Ribosome catalyse formation of peptide bonds between adjacent amino acids

What shape does tRNA have and why?

Cloverleaf shape due to hydrogen bonding within the molecule (the bond between complementary nitrogenous bases)

What's are the 5 differences between RNA and DNA?

Brings specific amino acids, each tRNA having an anticodon complementary to an mRNA codon.

Hydrogen bonds for between codon and anticodon (base pairing)

Ribosome catalyse formation of peptide bonds between adjacent amino acids

How many hydrogen bonds does Uracil form with adenine in RNA?

2

What are the 4 similarities between RNA and DNA?

1. They're both nucleic acids (polymers) made of nucleotide monomers.

2. Both contain a phosphate group

3. Both have ACG

4. Both form polymers in the same way by formation of phosphodiester bonds in condensation reactions

What happens to RNA molecules after protein synthesis?

They are degraded in the cytoplasm. The phosphodiester bonds are hydrolysed and the RNA nucleotides are released and reused.

Why do cells divide?

Growth and repair of tissues

The two daughter cells produced are identical. what does this mean?

They contain DNA with a base sequence identical to the parents.

What does semi-conservative mean?

After DNA replication, each new DNA molecule contains 1 original (parent) strand and one newly synthesised strand.
The original strand acts as templates for new complementary strands

Does DNA replication involve RNA?

NO bc replication is different to transcription

Describe the process of DNA replication fully

1. DNA helicase breaks the hydrogen bonds between complementary base pairs separating the strands

2. Each parent strand acts as a template.

3. Free nucleotides align opposite the template strands according to complementary base pairing and join via hydrogen bonds.

4. DNA polymerase catalyses the formation of phosphodiester bonds between nucleotides creating a new sugar phosphate backbone

5. 2 identical DNA molecules are produced one original strand and 1 newly synthesized strand for each og strand (semi conservative replication)

   
   

What is a mutation?

A change in the DNA base-sequence Can occur spontaneously or be caused by mutagens (chemicals + radiation)

What is the genetic code?

The sequence of nucleotide bases in DNA or mRNA that determines the sequence of amino acids in a protein. Read in triplets of bases called codons, each codon coding for 1 specific amino acid.

What does DNA code for?

A sequence of amino acids

What is a gene?

The section of DNA that contains the complete sequence of bases (codons) to code for an entire protein

How many codon combinations are possible?

64 because 4x4x4x4

How many amino acids are there?

20

What is a codon?

A sequence of 3 nucleotides in mRNA

What is the start codon?

AUG - codes for methionine if its in the middle of a protein

What are the three stop codons?

UAA, UAG, UGA
They don't code for any amino acids

Why is the genetic code degenerate?

Because more than 1 codon can code for a specific amino acid

What is the purpose of degenerate code?

1. It protects against mutations - a change in the sequence wont mean always mean that the protein will change.

2. Allows genetic variation without altering protein function

Why does transcription occur (4 reasons) ?

1. To produce an mRNA copy of a gene

2. So that the genetic code can be transferred from DNA in the nucleus to the ribosomes in the cytoplasm

3. Because DNA is too large to leave the nucleus +supply info to determine proteins amino acid sequence.

4. Allows protein synthesis to occur

Where is DNA contained?

Within a double membrane called the nuclear envelope that encloses the nucleus.

What is the function of the nuclear envelope?

This protects the DNA from damage in the cytoplasm.

Where does protein synthesis occur ?

At the ribosomes in the cytoplasm

What is transcription?

synthesis of an RNA molecule from a DNA template strand

What are the similarities between transcription and replication?

1. Both involve unzipping DNA via breaking hydrogen bonds.

2. Both use complementary base pairing.

3. Both involve the formation of phosphodiester bonds.

4. Both require polymerase enzymes. 5.Both occur in the nucleus (in eukaryotes).

Does transcription require helicase?

No because the RNA polymerase itself unwinds the DNA strands

What are the differences between transcription and replication?

1. Replication produces 2 identical DNA molecules, transcription produces RNA
   

2. Replication: The whole DNA molecule is copied, in transcription only a single gene is copied

3. Replication bases used: ATCG, transcription bases used: AUCG

4. Replication enzyme: DNA polymerase, Transcription: RNA polymerase
   

5. Replication: helicase required, Transcription, not required bc RNA unwinds DNA strands

How many strands of DNA contain the code for the protein to be synthesised and what is it called?

1 strand called the antisense strand

Runs from 5' to 3'

What is the strand that doesn't code for a protein called and what is its function?

Called the antisense strand (runs from 3' to 5') Acts as the template strand during transcription so that the complementary RNA strand formed carries the same base sequence as the sense strand

What happens once the antisense strand (the template strand) is exposed ?

Free RNA nucleotides will base pair with complementary bases exposed on the antisense strand where the dna unzips

Why happens at the end of transcription?

MRNA detaches form the DNA and leaves the nucleus via the nuclear pores.

What is rRNA?

Ribosomal RNA, a type of RNA found in ribosomes

What does rRNA do?

Helps position mRNA and tRNA correctly during translation. Catalyses peptide bond formation between amino acids

Where is rRNA synthesised?

In the nucleolus of eukaryotic cells

What is tRNA?

Transfer RNA, a type of RNA involved in translation

What shape is tRNA and why?

Has a cloverleaf shape due to hydrogen bonding within the molecule

What does tRNA do?

Carries a specific amino acid at the 3' end (of tRNA itself) Contains an anticodon that is complementary to an mRNA codon Ensures the correct amino acids is delivered to the ribosome for polypeptide/protein synthesis.

What is the binding site for mRNA and tRNA?

ribosomes

What 3 things do cells require energy for?

1. Synthesis - e.g of large molecules like proteins

2. Transport- e.g pumping molecules or ons across cell membranes by active transport

3. Movement- for example protein fibres in muscle cells that cause muscle contraction

What does atp stand for?

adenosine triphosphate

What does an ATP molecule consist of?

A nitrogenous base, a pentose sugar and three phosphate groups - its a nucleotide

How is the structure of ATP similar +diff to the nucleotides of RNA and DNA?

1. It has phosphate groups, but it has 3 and DNA and RNA nucleotides have 1
   

2. It has a nitrogenous base but for DNA and RNA nucleotides there's 4 types but for ATP its always adenine

3. It's pentose sugar is ribose like RNA (DNA is deoxyribose)

What is the reaction to remove a phosphate group from ATP

Hydrolysis (addition of water)

What is the equation for the hydrolysis reaction to remove a phosphate group in an ATP molecule?

ATP+H20—->ADP+Pi+energy

What does ADP stand for?

adenosine diphosphate

What is Pi?

inorganic phosphate

Why is ATP not a good LONG term energy store?

Due to the instability of its phosphate bonds it will keep breaking down

What is a better long term energy store than ATP?

The breakdown of Fats and Carbs molecules (called cellular respiration) is used to create ATP

How does ATP created during cellular respiration?

By reattaching a phosphate group to an ADP molecule This process is called phosphorylation Bc water is removed in this process,its a condensation reaction

Why is ATP a good IMMEDIATE energy store?

Due to the instability of ATP, cells don't store large amounts of it.
But ATP is rapidly reformed by the phosphorylation of ADP.
This intro conversion of ATP and ADP is constantly happening in living organisms meaning cells done need a large store of ATP

What are the 5 properties of ATP?

1. Small - moves easily into, out of and within cells
   2. Water soluble- energy requiring processes happen in aqueous environments
   3. Contains bonds between phosphates with intermediate energy -large enough to be useful for cellular reactions but not so large that energy is wasted as heat
   4. Releases energy in small quantities- quantities are suitable to most cellular needs, so that energy isn't wasted as heat
   5. Easily regenerated - can be recharged with energy