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Biology > 2.3 Nucleic acids > Flashcards

2.3 Nucleic acids Flashcards

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1
Q

What is the monomer for DNA?

A

Nucleotides

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2
Q

What is the structure of a nucleotide for DNA?

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A 
Phosphate group (-)
Pentose sugar (Deoxyribose) [Contains H]
Nitrogenous base
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3
Q

What is the structure of a nucleotide for RNA?

A 
Phosphate group (-)
Pentose sugar (Ribose) [Contains OH hydroxyl group]
Nitrogenous base
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4
Q

What are the different types of nitrogenous bases?

A

-Purines = double ring structures
(adenine and guanine)
-Pyrimidines = single ring structures
(thymine, cytosine and uracil)

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5
Q

How are nucleotides formed and broken?

A

-Formed: Condensation reaction between the phosphate and the sugar & the sugar and the base
This would produce two water molecules
-Broken: Hydrolysis reaction between the phosphate and the sugar & the sugar and the base
This would use up two water molecules

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6
Q

What is the structure of DNA?

A
  • Sugar phosphate backbone
  • Nitrogenous base pairs join to make the rungs
  • Held together by weak hydrogen bonds
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7
Q

What are the base pairs?

A
  • A purine always binds to a pyrimidine so that the rungs of the ladder are always the same length:
  • Adenine joins to thymine
  • Cytosine joins to guanine
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8
Q

How are the base pairs joined?

A
  • Two hydrogen bonds between A & T (or U)

- Three hydrogen bonds between C & G

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9
Q

How would you describe the way that the strands of the DNA run?

A
  • The two strands run in an anti parallel fashion (5-3 on one side and 3-5 on the other side)
  • The two strands are also twisted into a double helix
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10
Q

What is the structure of DNA? (9)

A
  • DNA is a polymer composed of many repeating subunits (monomers) called nucleotides
  • Each nucleotide is made up of a pentose sugar, a phosphate group and a nitrogenous base
  • These three molecules form nucleotides via two condensation reactions producing two molecules of water
  • In the DNA molecule there are two strands that run in an antiparallel fashion due to the reversal of the direction of the deoxyribose sugar
  • The sugar phosphate forms the backbone of the DNA
  • The sugar and phosphate groups are held together by strong covalent phosphodiester bonds
  • The nitrogenous bases on each strand are bonded with weak hydrogen bonds in the middle of the DNA, according to their complimentary base pairings (A&T with 2 hydrogen bonds and C&G with three hydrogen bonds)
  • As the bases always bond to complimentary pairing it means that when the DNA replicates, the sequence on one strand can be used to determine the sequence of bases on the other strand due to the complimentary base pairing
  • A pyrimidine will always bind to a purine to ensure the same length on each of the rungs
  • The DNA strands are also twisted to form a double helix structure
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11
Q

What are the steps of DNA replication?

A

1) DNA starts as a double helix
2) DNA gyrase untwists the helix and DNA helicase unzips the helix, breaking the hydrogen bonds
[Single stranded binding proteins prevent reannealing of the strands after helicase unzips the helix]
3) DNA polymerase binds to the leading strand and moves along it, this helps form the covalent/ phosphodiester bonds between the free DNA nucleotides and the strand
[The DNA polymerase moves in the 5’-3’ direction]
4) On the lagging strand the DNA polymerase binds and forms the covalent bonds from the 5’-3’ but going in the opposite direction
7) DNA ligase closes the gaps where DNA polymerase cannot bind this is because ligase can build from 3’-5’
8) DNA replication is completed semi conservatively as each new molecule of DNA has one old and one new strand

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12
Q

How does the Mesleson and Stahl experiment support the idea of semi conservative replication for DNA?

A

The DNA was made up of an equal mixture of N14 and N15, this was because the two new N14 strands joined each strand, so they are made of one N14 and one N15

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13
Q

What is transcription?

A
  • When DNA turns into mRNA
  • Occurs in the nucleus
  • Involving the enzyme: RNA polymerase
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14
Q

What is the process of transcription?

A

The process begins when a gene is triggered to be used, this causes transcription factors to bind to the gene

1) A gene is unzipped by helicase, breaking the hydrogen bonds
2) RNA polymerase binds to the gene to then catalyse the temporary binding of free nucleotides to the template strand
3) This produces a mRNA strand that is complimentary to the template strand and the same as the coding strand but T’s are replaced with U’s
4) The mRNA then leaves the nucleus via the nuclear pores to then attach to ribosomes

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15
Q

What is the process of translation?

A

1) The mRNA binds to a ribosome via the small subunit, then the large binds
2) 2 amino acids come in and joins the tRNA
3) The anticodon on the tRNA is complimentary to the codon on the mRNA, temporary hydrogen bonds then form between the two
4) Peptide bonds between the amino acid and the tRNA’s are transferred to the two amino acids, this forms the peptide bond between the two amino acids on the tRNA’s
5) The ribosomes move along and a new complimentary tRNA comes in, peptide bonds continue to be formed between each amino acid, forming a sequence of amino acid as the ribosome moves along and new tRNA’s come in
6) A polypeptide is formed from the sequence of amino acids
7) The polypeptide finishes forming and the amino acid sequence stop when a stop codon is hit, this is because there is no complimentary anticodon on a tRNA for the stop codon to temporarily bind to, to create more amino acids so the amino acid sequence stops
8) mRNA moves away from the ribosome and the ribosome has finished the process of translating
8) The polypeptide is formed, then secondary and tertiary structure is then formed to give 3D structure of the protein

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16
Q

What are the differences between DNA and RNA nucleotides?

A

1) DNA has Deoxyribose sugar
RNA has ribose sugar

2) DNA stores and transmits genetic information
RNA acts as a template for making proteins

3) DNA has ADENINE-THYAMINE
RNA has ADENINE-URICILE

4) DNA is found in the nucleus only
RNA is found everywhere in the cell

5) DNA is contained only in the nucleus
RNA is small enough to fit through pores in the nuclear membrane.

17
Q

What are the similarities between DNA and RNA nucleotides?

A

1) Both made up of sugar, a nitrogenous base and a phosphate group
2) They both play a part in the making of proteins
3) Both have the cytosine guanine pair of bases

18
Q

What are the different types of RNA?

A
  • Ribosomal RNA (rRNA)
  • Messenger RNA (mRNA)
  • Transport RNA (tRNA)
19
Q

Why does one strand run 5’ to 3’ but the other strand runs 3’ to 5’?

A
  • The strand that runs 5’ to 3’ is “The right way up” as the 5 carbon is the highest carbon on the pentose sugar
  • The 3’ to 5’ strand is inverted 180° “Upside down” so the 3rd carbon is then the highest in the chain so it runs 3’ to 5’
20
Q

Why is the overall structure of DNA sometimes referred to as a “Ladder”?

A
  • The sugar and phosphate molecules face outwards and the nitrogenous base pairs face inwards
  • DNA is sometimes referred to as a “Ladder” as the backbone of the sugar makes up the sides of the ladder and the nitrogenous bases are compared to the rungs of the “Ladder” in the centre of the DNA
21
Q

What is the bond between a sugar and phosphate group on one nucleotide and a phosphate group on another nucleotide called?

A

A phosphodiester bond

22
Q

What is the purpose of single stranded binding proteins in DNA replication?

A

-Single stranded binding proteins prevent reannealing of the strands after helicase unzips the helix

23
Q

How is it easier for the DNA polymerase to go in 5’ to 3’ prime on the leading strand rather than the lagging strand?

A
  • On the leading strand the DNA polymerase goes up toward the replication fork, this means that the strands are continuously being separated so the DNA polymerase can follow the strand upwards
  • On the lagging strand the DNA polymerase must go down, away from the replication fork, this means that the strand must be built in sections called Okazaki fragments, this Okazaki fragments are short parts of the strand which have small gaps where the strand could not be built, DNA ligase has to close the gaps between the Okazaki fragments to form a continuous strand
24
Q

What is a codon on a mRNA strand?

A
  • A codon is 3 bases on the mRNA strand that is read by the anticodon on tRNA
  • The codon codes for a protein, the anticodon on the tRNA reads the bases on the codon and makes the protein that the bases code for
25
Q

What are the benefits of coding for amino acids via base pairs and codons?

A
  • The code is universal so every single living organism will use the same code
  • This is evidence that organisms evolved from a single common ancestor which was the first to have this code seen in all organisms on earth
  • The code is degenerate, this means that several different codons can code for the same protein because there are more potential codes than amino acids
26
Q

What are stop codons?

A

-Base sequences that don’t have an amino acid associated to them

27
Q

What are ribosomes made from?

A
  • Proteins

- Ribosomal RNA

28
Q

How can ribosomes be used to view evolutionary relationships?

A
  • 16s rRNA is a component of ribosomes that is a universal part of cellular machinery that all living species have
  • By analysing and comparing the differences between several species’ 16srRNA it allows us to view evolutionary relationships

Biology (23 decks)

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