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Biology: Unit 2 > 2.3 Nucleic acids > Flashcards

2.3 Nucleic acids Flashcards

1
Q

What is a double helix?

A

Shape of DNA molecule, due to coding of two sugar phosphate backbone strands into right-handed spiral configiration

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1
Q

What is a monomer?

A

Molecule that when repeated makes a polymer

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2
Q

What is a nucleotide?

A

A molecule consisting of five-carbon ring (pentose) sugar, a phosphate group and a nitrogenous base

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3
Q

What is a polynucleotide?

A

A large molecule containing nucleotides

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4
Q

What do nucleotides do?

A

Form monomers of nucleic acid, DNA and RNA
* In DNA pentose sugar = deoxyribose
* In RNA pentoe sugar = ribose

They become phospholysed nucleotides when they contain more than one phosphate group

Help regulate many metabolic pathways

May be components of coenzymes

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5
Q

What is the structure of DNA?

A
  • It is a polymer as it is made up of many repeating units called nucleotides
  • A molecule of DNA consists of two polynucleotide strands
  • The two strands run in opposite directions so they are described as parallel
  • Each DNA nucleotide consists of a phosphate group, a pentose sugar called deoxyribose and one of four nitrogenous bases
  • The covalent bond between the sugar residue and the phosphate group in the nucleotide is called a phosphodiester bond - These bonds are broken when polynucleotides are synthesised
  • DNA molecules sare long and so they can carry a lot of encodeed genetic information
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6
Q

What are is a purine?

A
  1. 2 rings
  2. adenine and guanine
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7
Q

What is a pyrimidene?

A
  1. 1 ring
  2. thymine and cytosine
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8
Q

What holds the two antiparallel DNA strands between the nitrogenous base together?

A

Hydrogen bonds

This allows the molecule to unzip for transcription and replication

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9
Q

How much hydrogen bonds do each base pairs have?

A

A-T has 2
C-G has 3

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10
Q

Why does a purine always pair up with a pyrimidene?

A

This is because it gives it equal sized rungs on the DNA ladder. They can then twist into the double helix.

This gives the molecule stability

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11
Q

What is the 5’ end?

A

Where the phosphate group is attached to the fifth carbon atom of the deoxyribose sugar

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12
Q

What is the 3’ end?

A

Where the phosphate group is attached to the third carbon atom of the deoxyribose sugar

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13
Q

What is on the rungs of the ladder?

A

The complementary base pairs joined by hydrogen bonds

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14
Q

What are the 4 proteins involved in DNA replication

A

DNA gyrase
DNA helicase
DNA polymerase
DNA ligase

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15
Q

What does DNA gyrase do?

A

It untwists the double helix

16
Q

What does DNA helicase do?

A

It breaks the hydrogen bonds, unzipping the double strand

17
Q

What does DNA polymerase do?

A

It creates a new DNA strand
Builds the phosphate sugar backbone using free complementary backbone
Builds 5’ to 3’

18
Q

What does DNA ligase do?

A

Bonds the fragments to create a continuous DNA strand

19
Q

mention the proteins involved

What do are the steps of DNA replication?

A
  1. The double helix is untwisted by DNA gyrase
  2. DNA helicase breaks the hydrogen bonds, unzipping the double strand
  3. The bases are exposed and primers of RNA create a latching on point
  4. DNA polymerase creates a new DNA strand, builds the phosphate sugar backbone using free complementary nucleotides
  5. DNA polymerase builds 5’ to 3’. One strand is continuous following behind the helicase (leading strand). Lagging strand is made in fragments called okazaki fragments
  6. DNA ligase bonds the fragments to create a continuous DNA strand
  7. DNA replication occurs simultaneously in multiple places
  8. Semi conservative replication occurs and the new double helix is half old, half new
20
Q

What is a codon?

A

A sequence of 3 bases on the mRNA strand

21
Q

What is the process of transcription?

A
  1. Gene unwinds and unzips
  2. Hydrogen bonds between complementary nucleotides break
  3. RNA polymerase catalyses the formation of temporary hydrogen bonds bewteen temporay nucleotides and the complementary unpaired bases. This DNA strand is called the template strand
  4. A length of RNA that is complementary to the template strand of the gene is produced. It is therefore a copy of the other DNA strand - the coding strand
  5. The mRNA now passes out of the nucleus through the nuclear envelope and attaches to a ribosome
22
Q

What are the similarities between DNA replication and Transcription

A
  • Polymerase builds the sugar phosphate backbone (phosphodiester bond)
  • Copying using complementary base pairing
  • Both unwind, unzip (break hydrogen bonds)#
  • 5’ —> 3’ write/bond
23
Q

What are the differences between DNA replication and transcription?

A

DNA replication:
* 4 enzymes
* produces 2x DNA
* happens for replication

Transcription
* RNA rolymerase (1 enzyme)
* DNA –> mRNA
* producing mRNA

24
Q

What is the process of Translation?

A

Once the modified mRNA has left the nucleus it attaches to the small subunit of the ribosome at the start codon.
1. The tRNA molecule with the complementary anticodon to the start codon aligns opposite the mRNA, held in place by the ribosome. The ribosome can hold 2 tRNA molecules at a time
2. The two amino acids that have been delivered by the tRNA molecule have joined together by a peptide bond that is catalysed by an enzyme using ATP
3. The ribosome will move along the mRNA molecule to the next codon and another complementary tRNA will attach to the next codon on the mRNA
4. The continues until the ribosome reaches the stop codon at the end of the mRNA molecule causing the ribosome to detach and end translation
5. The polypeptide chain is now created and will enter the golgi body for folding and modification

25
Q

What are the features of genetic code?

A
  • Degenerate
  • Universal
  • Non-overlapping
26
Q

What is degenerate?

A

Amino acids are coded for by more than one triplet of bases

27
Q

What is universal?

A

The same triplet of bases codes for the same amino acid in all organisms

28
Q

What is non-overlapping?

A

Each base in a gene is only part of one triplet of bases that codes for one amino acid. Each codon or triplet of bases is read as a discrete unit

29
Q

DNA precipitation

A
  1. Homonogenise the cell with detergent. This will break open the cells and cell membranes to release their contents
  2. Filter to remove large debris
  3. Add salt to break hydrogen bonds between the DNA and water molecules
  4. Add protease to digest the proteins associated with the DNA
  5. Add ice-cold ethanol to precipitate out the DNA from the solution. The DNA appears as white strands

Biology: Unit 2 (12 decks)

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