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A LEVEL BIOLOGY > 2.1.3 Nucleotides and nucleic acids > Flashcards

2.1.3 Nucleotides and nucleic acids Flashcards

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1
Q

nucleotides

A

-made from a pentose monosaccharide(5carbons), a nitrogenous base and a phosphate group(negative charge)
-monomer of a nucleic acid(C,H,O,N,P)

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2
Q

why are nucleotides important?

A

-make up DNA(stores genetic info), RNA(makes proteins from DNA instruction)
-makes up ADP and ATP(store and transport energy in cells)

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3
Q

DNA nucleotides

A

-made up of a deoxyribose sugar(type of pentose monosaccharide with a H group on carbon 2), base(A,T,C or G) and a phosphate group(same in every DNA nucleotide)
-each DNA molecule is made up of 2 polynucleotide chains

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4
Q

DNA structure

A

-composed of 2 polynucleotide strands joined in a double-helix shape via hydrogen bonds between complementary bases pairs
- A+T has 2 H bonds and C+G has 3 H bonds
-polynucleotide strands run antiparallel so they can twist to form helix(ONLY STRANDS)
-nucleotides joined up by phosphodiester bonds
-also joined up between purines&pyrimidines
(two nucleotides on the same strand are adjacent nucleotides)

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5
Q

how are polynucleotides formed?

A

-nucleotides join up between the phosphate group one nucleotide and the sugar of another(carbon 5) via a condensation reaction forming a phosphodiester bond.

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6
Q

what is a chain of sugars and phosphates called?

A

a sugar phosphate backbone

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7
Q

How does the pairing of bases allow identical copies of DNA to be made?

A

-through the formation of 2 H bonds between A+T and 3 H bonds between C+G via complementary base pairing
-purines can only bind to pyrimidines because they are different shapes
-if one base is known, it can only pair with one other base

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8
Q

RNA nucleotides

A

-made up of ribose sugar(hydroxyl group attached to carbon 2), phosphate group and a base(A,U,C,G)

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9
Q

What are purines and pyrimidines?

A

-types of bases in DNA/RNA nucleotides

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10
Q

purines

A

-base that contains TWO carbon-nitrogen rings joined together
-adenine + guanine

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11
Q

pyrimidines

A

-base that contains ONE carbon-nitrogen ring
(smaller than a purine)
-cytosine, thymine and uracil

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12
Q

What are ADP and ATP?

A

-they are phosphorylated nucleotides
-have one or more phosphate groups added to it

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13
Q

ADP(adenosine diphosphate)

A

-contains adenine, ribose and 2 phosphate groups
- can be phosphorylated to form ATP so a phosphate bond (stores energy) is formed
-ATP can then be broken back down into ADP + an inorganic phosphate when energy is needed by a cell

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14
Q

ATP(adenosine triphosphate)

A

-contains adenine, ribose and 3 phosphate groups
-energy carrying molecule that provides energy to drive many processes inside living cells.

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15
Q

Why does DNA replicate?
(semi-conservative replication)

A

-this is required before cell division so each new cell has the full amount of DNA
-important for growth of new cells and repair of cells

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16
Q

STEP 1

A

-happens in the nucleus because DNA is too large to move so double helix structure must UNWIND
-catalysed by DNA gyrase

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17
Q

STEP 2

A

-DNA helicase breaks down hydrogen bonds between complimentary pairs and exposes the DNA strands
-DNA NUCLEOTIDE UNZIPS

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18
Q

STEP 3

A

-each original single strand acts as a template for a new strand
-free floating/activated DNA nucleotides in the nucleus join to the original exposed nucleotides by complementary base pairing

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19
Q

What direction does DNA polymerase work in? Why is this an issue?

A

-works in 5’ to 3’ direction to synthesise sugar-phosphate backbone
-DNA is antiparallel so only one of the template strands is in this orientation(leading strand), which means one strand can be synthesised continuously and the other(lagging strand) discontinuously.

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20
Q

How can the lagging strand issue be solved?

A

-DNA polymerase synthesises short fragments of the lagging strand called Ozaki fragments joined together with ligase.

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21
Q

STEP 4

A

-Adjacent nucleotides are
joined by phosphodiester bonds
-formed in condensation reactions using DNA polymerase
-forms a sugar-phosphate backbone and H bonds form between template bases and free floating bases(A+T have 2, C+G have 3)

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22
Q

STEP 5

A

-polynucleotide strands twist to form double helix
-new DNA molecules formed, made up of half of the original template and half of the new daughter cells through the process of semi-conservative replication

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23
Q

What is a gene?

A

-sequence of DNA nucleotides that codes for production of a specific sequence of amino acids that make up a specific polypeptide

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24
Q

Why is the order of nucleotide bases in a gene important?

A

-determines the order of amino acids in a particular protein
-different base code sequences(triplet)code for different amino acids
(template used to make proteins in protein synthesis)

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25
Q

why are the sequence of amino acids important?

A

-forms the primary structure of a protein
(different proteins have different numbers/sequences of amino acids)

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26
Q

What is every 3 nucleotides called in RNA?

A

a codon that codes for ONE AA

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27
Q

What is every 3 nucleotides called in DNA?

A

triplet code that codes for AA.

28
Q

The genetic code

A

-sequence of base triplet(codons) in DNA and RNA which codes for a specific amino acid
- non-overlapping= each triplet/codon is only read once and
triplets don’t share any bases.
-universal= every triplet/codon is the same in all organisms
-degenerate= one AA can have multiple triplets/codons

29
Q

How is DNA organised in eukaryotes?

A

-DNA is in a long line wrapped around histones to form a rod-like structure
-then organised into chromosomes

30
Q

What is the role of chromosomes?

A

-carry the genetic information of the cell within the nucleus

31
Q

How are genes organised in the chromosomes?

A

-Each gene will have a specific loci on the chromosome

32
Q

What are alleles?

A

-the different versions of a gene you can have at a loci
-All humans have the same genes, what makes us different are the alleles

33
Q

How are humans diploid?

A

-they have two alleles at each genetic loci, with one allele inherited from each parent

34
Q

Why does DNA wrap around histones?

A

-Histones are positively charged and DNA is negatively charged so they attract
-provides structural support for a chromosome

35
Q

What are stop and start codons?

A

-stop codons cause the ribosome to de attach and stop translation
-start codons(triplet code) mark the start of a translating region

36
Q

differences between DNA and RNA

A

-DNA contains thymine whereas RNA contains uracil
-DNA has deoxyribose in the nucleotide(has hydroxyl group on carbon 2) RNA has ribose in the nucleotide(doesn’t have hydroxyl group on Carbon 2)
-DNA is double stranded and RNA is usually single stranded(RNA is shorter)

37
Q

similarities between DNA&RNA

A

-both share the bases A, C and G
-both T and U are pyrimidines and pair with adenine
both have sugar phosphate backbone
both have a pentose sugar, phosphate group and bases.

38
Q

Why does protein synthesis take place?

A

-DNA is too large to move out of the nucleus and into the cytoplasm where ribosomes are.
-must be copied(transcription) and mRNA must leave the nucleus and join with a ribosome in the cytoplasm to synthesise a protein(translation).

39
Q

What is transcription?

A

First section of protein synthesis
-mRNA is used to copy a section of DNA
transcript for a polynucleotide in the nucleus because DNA is too big to transport to the ribosome

40
Q

Step 1 of transcription: unwinding

A

-DNA helicase catalyses a local(small section) unwinding of the DNA strands by breaking H bonds between complimentary base pairs through formation a transcription bubble. One of the strands is now used as a template strand

41
Q

Step 2:
complimentary base pair

A

-RNA polymerase binds to DNA and lines up free floating nucleotides to CBP along the template strand(A+U form 2 H bonds, C+G form 3)

42
Q

Step 3:
Condensation Reaction

A

-RNA polymerase catalyses formation of phosphodiester bonds between adjacent nucleotides to form sugar-phosphate backbone

43
Q

Step 4:
Assembling mRNA strands

A

-RNA polymerase moved down the template strand to assemble mRNA.
-newly formed strand begins to leave DNA via the nuclear envelope as H bonds between template strand breaks

44
Q

Step 5:
Terminating Sequence reached

A

-until RNA polymerase reaches a stop codon and gets kicked off template strand which stops mRNA production.

45
Q

What is post-transcriptional editing?

A

-mRNA is edited between transcription and translation

46
Q

What are introns?

A

-non coding regions in DNA that play a role in gene expression

47
Q

What happens to introns during PTE?

A

-go through the process of ‘splicing’ where they are cut out of the mRNA as it is not needed for protein synthesis

48
Q

What are exons?

A

-coding regions of DNA that code for proteins

49
Q

What happens to exons during PTE?

A

-makes up the mRNA transcript which leaves the nucleus through nuclear pores

50
Q

What is translation?

A

-second stage of protein synthesis
-translating the code on mRNA into a protein to form a polypeptide chain in the ribosomes in the cytoplasm

51
Q

Step 1:
INITIATION

A

-tRNA transports its specific AA to the ribosomes where it binds to the mRNA
-tRNA with the complimentary anti codon and the specific AA attached will bind onto the start codon of mRNA by CBP.

52
Q

Step 2:
Elongation

A

the protein at the first tRNA will form a dipeptide bond with the protein at the next tRNA which is catalysed by rRNA and uses ATP
-the tRNA molecule will leave and the dipeptide bond moves to the next tRNA.
-3rd tRNA binds to next codon of mRNA and its AA binds to the first two and the 2nd tRNA moves away.

53
Q

Step 3:
Termination

A

-process continues, forming a polypeptide chain until a there is a stop codon on the mRNA
-polypeptide chain is transported in vesicle from RER where goes through processing to the golgi apparatus, where it is packaged into a secretory vesicle
-vesicle moves along cytoskeleton and fuses with cell surface plasma membrane via exocytosis

54
Q

What happens if DNA replication is not accurate?

A

a spontaneous mutation will occur
-affects conservation of genetic information as it changes DNA sequence(can alter sequence of amino acids and therefore produce an abnormal protein)
-may not have an effect on protein function, worsen it or better it

55
Q

Structure and role of mRNA

A

-single poly(rna)nucleotide strand(made in the nucleus during transcription) arranged in a helix shape*
-group of 3 adjacent bases are called codons
-carries the genetic code from the DNA in the nucleus to the ribosomes for protein synthesis
*represented as a straight strand to make it easier to understand processes involving RNA.

56
Q

Structure and role of tRNA

A

-single polynucleotide strand that is folded into a clover shape held together by H bonds between base pairs
-has a sugar phosphate backbone
-has a specific sequence of 3 bases called an anticodon that is complementary to mRNA & an AA binding site at the end
- carries AA’s that are used to make proteins to the ribosome

57
Q

Structure and role of rRNA

A

-forms the 2 subunits(large and small) in a ribosome along with proteins
-ribosome moves along the mRNA strand during protein synthesis.
-rRNA helps catalyse the formation of peptide bonds between amino acids

58
Q

what is ATP used for?

A

-currency of energy in organisms(how it is transferred)
-energy is used for synthesis, transport and movement
-constantly recycled and only used as short term energy storage

59
Q

How does ATP release energy?

A

-liberation of the 3rd phosphate
-phosphate bond breaking via hydrolysis requires a small amount of energy to release a large amount of energy
-the free phosphate can phosphorylate something else and ADP gets converted back into ATP via energy released in respiration

60
Q

why is ATP a good short term energy store?

A

-small(can easily move in and out of cells)
-water soluble due to phosphate group(energy requiring processes can happen in aq solutions)
-releases a small amount of energy(not enough for wasted energy or thermal energy transfer)
-easily generated

61
Q

Limitations of ATP

A

-unstable phosphate bonds mean that ATP is not a good long term energy store
-fats and carbs are better as they can be broke down easy to release energy in respiration

62
Q

Why is ATP required?

A

-all organisms need it for anabolic reactions(building larger molecules from smaller ones) and moving substances across membrane or within cell
-animals need it for muscle contraction to coordinate movement and for conduction of nerve impulses

63
Q

Why do scientists need to purify DNA?

A

in order to analyse it

64
Q

Purifying DNA

A

-break up cell wall in your sample(grind for 10 secs)
-make up solution of detergent, salt and distilled water
-add plant extract to solution and incubate in a water bath at 60 degrees for 15 mins
-detergent will break down cell membrane/nuclear envelope and release DNA from nucleus, salt will cause DNA to precipitate and clump.
-temp prevents enzymes from working properly and breaking down DNA
-place beaker in ice bath to cool mixture and add protease to filtered mixture to break down histones
-dribble cold ethanol(causes DNA to precipitate) on side of tube to form a layer of DNA detergent mixture and once left for a few mins it will form a white precipitate which can be removed with glass rod.

65
Q

DNA structure and functions

A

-base sequence stores genetic info
-very large so it can store a massive amount of genetic info
-helix shape makes it compact

66
Q

Eukaryotic DNA vs Prokaryotic DNA

A

-nucleotide structure is identical
-nucleotides joined by phosphodiester bonds
-eu contains exons AND introns, pro only contains exons
-eu DNA is long and linear, pro DNA is short and circular
-eu is associated with histones, pro not associated with histones
-pro cannot form chromosomes

A LEVEL BIOLOGY (19 decks)

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