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Biology > 2.3. 1-3 Nucleic Acids > Flashcards

2.3. 1-3 Nucleic Acids Flashcards

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1
Q

Double Helix

A

shape of a DNA molecule, due to the coiling of the two-sugar phosphate backbone stands into a right handed spiral configuration.

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2
Q

Whats a monomer?

A

molecule that when repeated makes up a polymer. Amino acids are the monomers of proteins. Nucleotides are the monomers of nucleic acids.

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3
Q

What is a polynucleotide

A

Large molecule containing many nucleotides

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4
Q

Nucleotides

A
  1. Form nucleic acids, DNA and RNA.
    - RNA is a Ribose pentose sugar
    - DNA is an Deoxyribose pentose sugar
  2. Nucleotide become phosphorylated when they contain more than one phosphate group for example
    AMP:
    ADP:
    ATP: Energy rich end product of most energy releasing bio chemical. AND helps metabolic pathways
  3. May be components of coenzymes such as NADP
    NADP: Photosynthesis
    NAD, FAD, Coenzyme A: Respiration
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5
Q

Structures of DNA

A
  • Polymer made out of two polynucleotide stands
  • Two strands run in opposite directions
  • A phosphate group, 5 carbon sugar called deoxyribose and one of four nitrogenous bases Adenine, Thymine, Guanine, Cytosine
  • Covalent bond between the sugar residue and the phosphate group in a nucleotide is also called a phophodiester. These bonds break when nucleotide break down and are formed when polynucleotides are synthesised.
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6
Q

Purines and pyrimidines

A

Purines: Adenine or Guanine (two rings)
Pyrimidine: Thymine or Cytosine (One ring)

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7
Q

Importance of Hydrogen bonding:

A
  1. Adenine always pairs with thymine (two hydrogen bonds)
  2. Guanine always pairs with cytosine (3 hydrogen bonds)
  3. Purine always pairs with pyrimidine, giving equal sized rungs on the DNA ladder. These can then twist into a double helix. This gives it stability
  4. H bonds allow the molecule to unzip for transcription.
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8
Q

How its organised in cells

A

Eukaryotic cells:

  • DNA content , or the genome is in the nucleus
  • DNA is tightly wound around special histone proteins into chromosomes. Each chromosome is therefore a molecule of DNA.
  • Mitochondria = Loops of DNA

Prokaryotic cells

  • DNA is in loops and is within the cytoplasm, not enclosed in a nucleus
  • It is not wound around histone proteins and is described as naked.
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9
Q

What is DNA polymerase?

A
  • Enzyme that catalyses formation of DNA from activated DNA, using single stranded DNA as a template.
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10
Q

What is helicase?

A

Enzyme that catalyses the breaking of hydrogen bonds between the nitrogenous pairs of bases in a DNA molecule

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11
Q

What is semi-conservative replication

A

This is how DNA replicates, resulting in two new molecules, each of which contains one old strand and one new strand. One old strand is conserved in each new molecule.

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12
Q

DNA is a self replicating molecule.

A
  • All the DNA within a cell is called the genome
  • Every time the cell divides, the DNA has to be copied so that each new daughter cell receives the full set of instructions.
  • Replication takes place during Interphase (S) before the cell itself divides
  • The DNA within mitochondria and chloroplasts also replicates each time these organelles divide, which is just before the cell divides.
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13
Q

Semi-conservative replication

A

To make a copy itself each DNA molecule

  1. Unwinds- the double helix is untwisted, a bit at a time, catalysed by the gyrase enzyme.
  2. The molecule also unzips, hydrogen bonds between the nucleotide bases are broken. This is catalysed by DNA helicase, and results in two single strands of DNA with exposed nucleotide bases.
  3. Free phosphorylated nucleotide, present in the nucleoplasm within the nucleus are bonded to the exposed bases, following complementary base- paring rules
  4. The enzymes DNA polymerase catalyses the addition of the new nucleotide bases in the 5’ to 3’ direction, to the single strands of DNA; it uses each single strand of unzipped DNA as a template
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14
Q

Mutations

A
  • During DNA replications errors may occur and the wrong nucleotide may be inserted. This is estimated to occur in 1 in 10^8 base pairs. This could change the genetic code and is an example of point mutation.
  • During the replication process there are enzymes that can proofread and edit out incorrect nucleotide, reducing the rate of mutations.
  • Mutations may lead to alleles or gene variations giving a different version of a particular gene
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15
Q

What is a gene?

A

A length of DNA that codes for a polypeptide or for a length of RNA that is involved in regulating gene expression

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16
Q

Polypeptide

A

a polymer made of many amino acids units joined together by peptide bonds. Insulin is a polypeptide of 51 amino acids

17
Q

Protein

A

large polypeptide of 100 or more amino acids

18
Q

Transcription

A

the process of making messenger RNA from DNA template

19
Q

translation

A

formation of a protein, at ribosomes, by assembling amino acids into a particular sequence according to the coded instructions carried by DNA to the ribosome by mRNA

20
Q

How is RNA different?

A
  • Each sugar molecule is a Ribose
  • The nitrogenous base uracil, which is a pyrimidine replaces the pyrimidine base thymine.
  • Polypeptide chain is usually single-stranded
  • Shorter chains
  • RNA, mRNA, tRNA, rRNA
21
Q

How do protein shapes help with their functions

A
  • Shape of an active site of an enzyme molecule must be complementary to the shape of the substrate molecule
  • part of antibody molecule must be complementary to that of antigens on the surface invading pathogens
  • receptor on the cell surface membrane must have shape complementary to the shape of the cell-signalling molecules such as a hormone or a drug, that it must detect
  • Ion channel protein must have hydrophillic aminoacids lining the inside of the channel and lipophilic amino acids on the outside portion that will be next to the lipid bilayer of the plasma membrane
22
Q

What is a sequence of base triplets called?

A

Codons

23
Q

Nature of genetic code

A
  • Genetic code is universal, because in almost all living organisms the same triplet of DNA bases codes for the same amino acid.
  • Genetic code is described as degenerate because for all amino acids, except methionine and tryptophan, there is more than one base triplet. This made reduce the effect of point mutations, as a change in one base of triplet could produce another base triplet that still codes for amino acid.
  • The genetic code is also non-overlapping, and it is read starting from a fixed point in groups of three bases, If a base is added or deleted then it causes a frame shift, as every base triplet after that and hence every amino acid coded for is changed.
24
Q

How does transcription occur:

A
  1. Gene unwinds and unzips
  2. Hydrogen bonds between complementary nucleotide bases break
  3. Enzyme RNA polymerase catalyses the formation of temporary hydrogen bonds between RNA nucleotides and their complementary unpaired DNA bases.
    [(A)-T, (C)-(G), (G)-(C), (U)-(A)]. Template strand.
  4. Length of RNA that is complementary to the template strands of the gene is produced (Coding strand)
  5. mRNA now passes out of the nucleus through the nuclear envelope.
25
Q

tRNA

A
  1. tRNA is made in the nucleolus, they are a single stranded polynucleotide but can twist into a hairpin shape.
  2. At one end is a trio of nucleotide bases that recognises and attaches to a specific amino acid.
  3. At the other end there is another triplet of bases called an anticodon, that is complementary to a specific codon (triplet) of bases on rNA
26
Q

Translation:

A
  1. tRNA molecule brings the amino acids and finds their place when the anticodon binds by temporary hydrogen bonds to the complementary codon on the mRNA molecule
  2. As the ribosome moves along the length of mRNA, it reads the code, and when two amino acids are adjacent to each other a peptide bond is formed between them
  3. Energy in the form of ATP, is needed for polypeptide synthesis.
  4. Amino acid sequence for the polypeptide is therefore ultimately determined by the sequence of triplets of nucleotide bases on the legenth of DNA
  5. After the polypeptide assembled, MRNA

Biology (12 decks)

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