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AS BIO UNIT1 > 1.5 Nucleic Acids > Flashcards

1.5 Nucleic Acids Flashcards

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1
Q

Define a nucleotide

A

Monomer of nucleic acid comprising a pentose sugar (deoxyribose or ribose), a nitrogenous base and a phosphate group.
-all 3 sub components are joined in a condensation reaction

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2
Q

Pyrimidine bases

A

Thymine, cytosine and uracil

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3
Q

Purine bases

A

Adenine and guanine

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4
Q

In the structure of DNA, what bonds join the phosphate of one monomer to the pentose of another?

A

Phosphodiester bond

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5
Q

Define an autotrophic organism as well as the 2 sub types

A

-autotrophic: convert other forms of energy into chemical energy
-chemoautotrophic: use energy derived from oxidation of electron donors such as H2, Fe2+ (some bacteria and archaea)
-phototrophic: use light energy in photosynthesis (green plants)

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6
Q

Define a heterotrophic organism

A

-organisms that derive their energy from food, such as mammals and dentritvores

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7
Q

Where do organisms store chemical energy

A

Lipids and carbohydrates

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8
Q

How is energy released from ATP

A

-enzyme ATPase hydrolyses the bond between the 2nd and 3rd phosphate groups leaving only 2.
-ATP molecule is hydrolysed to ADP and an inorganic phosphate ion with the release of chemical energy
-exergonic reaction

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9
Q

How much energy does each hydrolysed mole of ATP produce?

A

30.6kJ

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10
Q

What is phosphorylation?

A

The addition of a phosphate to ADP

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11
Q

Advantages in having ATP as an intermediate in providing energy as oppose to glucose

A

-hydrolysis of ATP involves a small reaction releasing energy immiedately whereas breakdown of glucose involved many intermediates & takes longer
-only 1 enzyme needed for ATP but many for glucose
-ATP releases energy in small amounts when needed as oppose to large amounts at once
-AP provides a common source of energy for many different chemical reactions which increases the efficiency and control of the cell

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12
Q

Explain the roles of ATP

A

-metabolic processes - build large, complex molecules ie DNA synthesis
-active transport - allow molecules to be moved against concentration gradient
-movement - muscle contraction
-nerve transmission
-secretion

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13
Q

Describe the structure of DNA

A

-composed of 2 polynucleotide strands wound around each other in a double helix held together by hydrogen bonds.
- sugar-phosphate backbone joined by condensation reactions creating phosphodiester bonds
-pentose sugar is deoxyribose

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14
Q

Why is DNA antiparallel?

A

-polynucleotide strands run in opposite directions to allow for hydrogen bonding between complimentary base pairs

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15
Q

Why is DNA suited to its functions? (4)

A
  • very stable molecule and its genetic information passes essentially unchanged through generations
  • very large molecule so can carry lots of genetic information
  • 2 strands are able to separate as held by hydrogen bonds
  • base pairs are inside the double helix so the genetic information is well protected
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16
Q

Describe the structure of RNA

A
  • single stranded polynucleotide
  • contains pentose sugar ribose
  • contains adenine, uracil, cytosine and guanine
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17
Q

What is mRNA?

A
  • messenger RNA
  • long, single stranded molecule
  • synthesised in nucleus from a template strand of DNA and carries genetic code to ribosomes in cytoplasm via the nuclear pore
  • 3 bases = codon
  • varied length dependant on the genes they transcribe
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18
Q

What is rRNA?

A
  • ribosomal RNA
  • found in cytoplasm and comprises large, complex molecules
  • ribosomes are made of rRNA and protein
  • they are the site of translation of the genetic code into protein
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19
Q

What is tRNA?

A
  • transfer RNA
  • small, single stranded molecule that folds in so many places that there are base sequences forming complimentary pairs
  • cloverleaf shape
  • the 3’ end has CCA where the specific amino acid the molecule carries is attached
  • carries sequence of 3 bases called the anticodon
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20
Q

Who proposed the molecular structure of DNA and when?

A

James Watson and Francis Crick in 1953.

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21
Q

Where is DNA found?

A
  • eukaryotic cells: enclosed in the nuclei
  • prokaryotic cells: loose in the cytoplasm
    —> separate DNA also in mitochondria and chloroplasts
22
Q

What is DNA replication?

A

Where 2 complimentary strands of DNA separate and two identical double helices can be formed with each original strand acting as a parent template

23
Q

What is protein synthesis?

A

Where a sequence of bases represents the information carried in DNA and determines the sequence of amino acids in proteins

24
Q

When does DNA replication take place in eukaryotic cells?

A

Interphase

25
Q

What are the 3 theories of replication?

A
  • conservative
  • semi-conservative
  • dispersive
26
Q

What is the conservative theory?

A

-parental double helix remains in tact and a whole new double helix is made
—> INCORRECT

27
Q

What is the semi-conservative theory?

A
  • parental double helix separates into 2 strands, each of which acts as a template for the synthesis of a new strand
    —> CORRECT
28
Q

What is the dispersive theory?

A
  • two new double helices contain fragments from both DNA strands
    —> INCORRECT
29
Q

What is the Meselson Stahl experiment?

A
  • investigation into how DNA separates
30
Q

Step 1 of MS experiment

A
  • cultured bacterium e.coli for several generations in a broth containing amino acids and the heavy isotope 15N as oppose to the usual 14N found in nitrogenous bases
  • bacterium incorporate 15N into nucleotides and then DNA until it only has 15N
  • extract DNA and put in centrifugal tube
  • DNA settled low due to heavy 15N
31
Q

Step 2 of MS experiment

A
  • 15N bacteria were washed and transferred to a medium containing 14N and divided once more
32
Q

Step 3 of MS experiment

A
  • DNA from first gen culture is centrifuged and had a midpoint density
  • ruled out conservative as that would produce a heavy molecule
  • intermediate position could imply one strand was 14N and one was 15N showing semi- conservative but it could also be mixed strands showing dispersive
33
Q

Step 4 of MS experiment

A
  • DNA from 2nd gen grown in 14N settled at high and middle in equal amounts which rules out dispersive as only 1 band would form
  • one parental strand conserved which proves semi-conservative
34
Q

Explain the role of the enzyme DNA helicase in DNA replication

A
  • unwinds the double helix by breaking the hydrogen bonds between base pairs on the 2 antiparallel polynucleotide DNA strands to form 2 separate strands
35
Q

Explain the role of the enzyme DNA polymerase in DNA replication

A
  • catalyses condensation reactions between the activated nucleotides, forming phosphodiester bonds
  • synthesises the new strands from template strands
    —> releases 2 extra phosphates which gives ATP
36
Q

What is the role of free nucleotides?

A
  • also known as activated nucleotides or nucleoside triphosphates
  • align with complimentary bases on template DNA and are held by hydrogen bonds
  • when DNA polymerase forms the phosphodiester bonds, activated nucleotides lose 2 phosphate groups which releases energy needed for reaction
37
Q

What is DNA?

A
  • store of genetic information coded in the sequence of bases in the DNA
  • determined the characteristics of an organism
38
Q

What are the characteristics of DNA?

A
  • triplet code
  • 64 possible codes but only 20 amino acids - more than one code for the same amino acid (known as degenerate)
  • code is punctuated - 3 codes that do not code for AA. Known as stop codons in mRNA
  • universal - all organisms have the same triplet codes for the same amino acids
  • do not overlap
39
Q

What is an intron?

A

A non-coding nucleotide sequence in DNA and pre-mRNA that is removed from pre-mRNA to produce mRNA

40
Q

What is an exon?

A

A coding region in the nucleotide sequence of DNA and pre-mRNA that remains present in the final mRNA after introns are removed

41
Q

DNA makes new polypeptides. What has to happen in eukaryotic cells first?

A
  • RNA has to be processed first
  • initial code much longer than final
  • introns are cut out by endonucleases and remaining exons are joined by ligases
42
Q

Outline the process of protein synthesis

A

DNA is transcribed in the nucleus to RNA which is then translated to a polypeptide in the ribosome

43
Q

Define transcription

A

One strand of DNA acts as a template for the production of mRNA, a complimentary part of the DNA sequence.

44
Q

Explain transcription

A
  • DNA helicase enzyme breaks the H bonds between bases so the double helix unwinds and separates, exposing the nucleotide bases.
  • RNA polymerase binds to the template strand of DNA at the beginning of the sequence to be copied, forming hydrogen and phosphodiester bonds
  • free RNA nucleotides align opposite the template strand in order of complimentary bases
  • RNA polymerase moves along forming bonds that add nucleotides (synthesis of mRNA molecule)
  • strands rewind to form a double helix and the RNA polymerase separates from the template when it reaches a ‘stop’ codon
  • mRNA leaves via nuclear pore
45
Q

Define translation

A
  • sequence of codons on the mRNA used to generate a specific sequence of amino acids, forming polypeptides
46
Q

Translation takes place on a ribosome and involves tRNA. What are the 2 subunits of a ribosome?

A
  • large: 2 sites of attachment for the tRNA molecules
  • small: binds to mRNA
47
Q

Describe the initiation stage of translation

A
  • a ribosome attaches to a ‘start’ codon at one end of the mRNA molecule
  • first tRNA attaches to ribosome and the 3 bases on the codon of the mRNA bond to the 3 bases on the anticodon of tRNA by hydrogen bonds
  • second tRNA attaches to other attachment site in same manner
48
Q

Describe the elongation state of translation

A
  • 2 AA are close enough for the ribosomal enzyme to catalyse a peptide between them
  • the tRNA now leaves the attachment site so it’s vacant so the ribosome moves one codon along the mRNA so the next tRNA can bind
  • process repeated until polypeptide chain is formed
49
Q

Describe the termination stage of translation

A
  • the sequence repeats until a ‘stop’ codon is met
  • ribosome-mRNA-polypeptide complex separates
  • protein synthesis is complete
50
Q

2 uses of ATP in plant cell

A

Cell division, active transport

51
Q

Creatine phosphate increases ATP availability. Under what conditions is ADP -> ATP, and what conditions for ATP-> ADP

A

ADP -> ATP = exercise so ATP generated quickly due to creatine
ATP -> ADP = relax, creatine phosphate creates to be store of ATP

AS BIO UNIT1 (6 decks)

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