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A Level Biology > Nucleic Acids > Flashcards

Nucleic Acids Flashcards

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1
Q

What does DNA stand for

A

Deoxyribonucleic acid

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2
Q

What is a nucleotide

A

Biological molecule consisting of a five-carbon sugar, a phosphate group and a nitrogenous base

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3
Q

what is the structure of a nucleotide

A
  • phosphate esters of pentode sugars
  • nitrogenous base is linked to C1 of the sugar
  • phosphate group is linked to C5 of the sugar
  • these are bonded by covalent bonds due to condensation reaction
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4
Q

When do nucleotides become phosphorylated nucleotides

A

When they contain more than one phosphate group
- ADP
- ATP

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5
Q

How are nucleotides able to help with metabolic pathways

A
  • ATP
  • ADP
  • AMP
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6
Q

What is the structure of DNA

A
  • polymer. Many repeated nucleotide units
  • consist two polynucleotide strands
  • two strands run in opposite directions (anti parallel)
  • consist of a phosphate group, five carbon sugar (deoxyribose), one nitrogenous base
  • nitrogenous bases: adenine, guanine, thymine, cytosine
  • covalent bond between the sugar and phosphate group is called a phosphodiester bond
  • phosphodiester bonds broken and formed when polynucleotides are synthesised
  • long so can carry a lot of genetic coding
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7
Q

What is a purine

A

The nucleotide bases containing a double ring structure

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8
Q

what hydrogenous bases are purines

A

Guanine
Adenine

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9
Q

What is a pyramidine

A

Nucleotide base with one ring structure

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10
Q

What hydrogenous bases are pyramidine

A

Cytosine
Thymine
Uracil

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11
Q

What bonds are between hydrogenous pairs

A

Hydrogen bonds

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12
Q

How many hydrogen bonds are between adenine and thymine

A

2

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13
Q

How many hydrogen bonds are between guanine and cytosine

A

3

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14
Q

What gives DNA is helical structure

A

Purine is always paired with a pyrimidine.
- gives DNA ability to twist

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15
Q

What allows the DNA to unzip for transcription and replication

A

Hydrogen bonds
- weak
- easy to break

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16
Q

What part of the DNA is the 5’ end

A

The end of the molecule where the phosphate group is attached to the fifth carbon atom of the deoxyribose sugar

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17
Q

what part of the DNA is the 3’ end

A

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

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18
Q

What do the rungs on the DNA ladder contain

A

Complementary base pairs
- joined by hydrogen bonds

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19
Q

What does the antiparallel sugar-phosphate backbone do for the integrity of the DNA

A

Allows the molecule to be very stable
- integrity of the coded information within the base sequences is protected

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20
Q

How is DNA organised in eukaryotic cells

A
  • majority of DNA content is in the nucleus
  • each large molecule of DNA is wound around special histone proteins into chromosomes
  • each chromosome is one molecule of DNA
  • loop of DNA inside mitochondria and chloroplasts
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21
Q

How is DNA organised in prokaryotic cells

A
  • DNA is in a loop and is within the cytoplasm
  • not wound around histone proteins
  • described as naked
22
Q

What is the structure of RNA

A
  • pentose sugar (ribose)
  • phosphate group
  • nitrogenous base (uracil instead of thymine)
  • one strand
  • shorter strand
  • either mRNA, tRNA or rRNA
23
Q

What is the structure of ATP

A
  • ribose
  • adenine (nitrogenous base)
  • 3 inorganic phosphates (phosphate group)
24
Q

What is semi-conservative replication

A

How DNA replicated
- results in two new molecules
- each containing one old strand and one new strand
- one old strand is conserved in each new molecule

25
Q

How does a DNA molecule split into two

A

Unwinds - the double helix untwists, a little at a time, catalysed by a gyrase enzyme

Unzips - hydrogen bonds between nucleotide bases are broken. catalysed by DNA HELICASE. This results in two single strands of DNA with exposed nucleotide bases

26
Q

What happens after the DNA has been separated

A
  • free nucleotides, in the nucleoplasm, bond to the exposed bases. Using complementary base pairings
  • DNA POLYMERASE catalyses the addition of new bases from 5’ to 3’. DNA zips back together
  • leading strand is synthesised continuously
  • lagging strand is synthesised in fragments (discontinuous)
  • these fragments are then joined together by ligase
27
Q

What are the steps of DNA replication

A
  • unwinds
  • unzips
  • bases attach
  • zips back up
28
Q

How can mutations occur in replication

A

The wrong nucleotide may be inserted
- could change the genetic code (point mutation)

29
Q

What is a gene variation

A

Different variations of a particular gene

30
Q

What are the five main feature of genetic code

A
  • triplet code
  • non overlapping
  • degenerate
  • universal
  • determines amino acid sequence
31
Q

What is triplet code in genetic code

A
  • three bases (codon) code for an amino acid
  • the three complementary bases on tRNA form an anticodon
  • triplet codons for ‘start’ and ‘stop’ signals
32
Q

What does it mean when genetic code is non-overlapping

A

All of the codons are separate

33
Q

What does it mean when genetic code in degenerate

A

Most amino acids have more than one code

34
Q

What does it mean that genetic code is universal

A

All life on earth has the same DNA code for amino acids

35
Q

What does it mean by genetic code can determine amino acid sequences

A

DNA codes for RNA, this in turn codes for proteins
The proteins produced then form and regulate all other processes

36
Q

Examples of the primary structure of a polynucleotide being correct

A
  • shape of the active site must be complementary to the substrate
  • part of an antibody must have a complementary shape to the antigen on the surface of an invading pathogen
  • receptor of a cell membrane must have a complementary shape to the cell signalling molecule that it must detect
  • ion channel protein must have hydrophilic amino acids lining the outside of the channel
37
Q

What is translation

A

The process of making mRNA from a DNA template

38
Q

What is translation

A

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

39
Q

What are the steps of transcription

A
  • gene unwinds and unzips
  • hydrogen bonds break
  • RNA POLYMERASE allows nucleotides to bond to their complementary bases
  • length of RNA that is complementary to the template strand is produced
  • this forms coding strand
  • mRNA passes out nucleus and attaches to a ribosome
40
Q

What does the large subunit of ribosomes contain in translation

A

3 binding site
- E
- P
- A

41
Q

What happens at the A site

A

Where tRNA enters ribosome
- holds tRNA carrying the next amino acid to be added to the polypeptide chain

42
Q

What happens at the P site

A

Holds tRNA carrying the growing polypeptide chain
- where the codon and anticodon bind
- condensation reaction forms peptide bonds between amino acids

43
Q

What happens at the E site

A

Where the tRNA exits the ribosome
- site from which tRNA that has lost its amino acid is discharged

44
Q

What are the main steps of translation

A
  • small subunit of ribosome attaches to mRNA
  • tRNA attaches to mRNA
  • large subunit of ribosome attached around tRNA on mRNA
  • tRNA enters A site
  • polypeptide chain starts to grow
  • tRNA leaves E site
  • process continues
  • release factor enters A site
  • all elements are released resulting in a polypeptide chain
45
Q

What happens inside the large subunit of ribosome

A
  • anticodon of tRNA attaches to codon of mRNA
  • polypeptide chain is formed
46
Q

What does the mRNA carry in translation

A

The nucleotide code for the protein to be made

47
Q

What does tRNA do in translation

A

Interpret the molecule code
- each tRNA carries an amino acid and an anticodon

48
Q

What is the structure of tRNA

A

Clover structure
- D arm
- T arm
- anti codon
- acceptor stem (amino acid)

49
Q

What are the processed of protein synthesis

A
  • DNA unzips: DNA helicase
  • DNA polymerase bonds adjacent nucleotides
  • hydrogen bonds form and helix returns
  • pre mRNA leaves through nuclear pores
  • turn into mature mRNA with splicing
  • tRNA brings amino acid into ribosome subunit (A site)
  • codon and anticodon bind (P site)
  • polypeptide chain grows
  • tRNA leaves ribosome (E site)
  • amino acid binds to tRNA (tRNA activation)
50
Q

What is splicing

A

The process by which introns, no coding regions of genes, are taken out of the mRNA transcript. Exons, coding regions, are joined together to make mature mRNA

A Level Biology (13 decks)

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