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Alevel biology > Nucleotides & Nucleic Acids > Flashcards

Nucleotides & Nucleic Acids Flashcards

1
Q

what are the two types of nucleic acid?

A

deoxyribonucleic acid (DNA)
ribonucleic acid (RNA)

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2
Q

what is DNA?

A

the base sequence of DNA codes for the sequence of amino acids in a polypeptide
has a role in the storage of genetic information
has a double helix - the strands run anti parallel
compact shape - coils into chromosomes
longer than RNA - large amounts of info stored
complementary base pairing - A T and C G
sugar-phosphate backbone - stable molecule
has deoxyribose pentose sugar (1 less oxygen than ribose)

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3
Q

what is RNA?

A

used in protein synthesis
has a role in the transfer of genetic information
single helix
shorter than DNA
A U C G bases
no base pairs
has ribose pentose sugar

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4
Q

what are nucleotides?

A

monomers that make up nucleic acids
made from three components:
- phosphate
- pentose five carbon sugar
- organic (contain carbon) nitrogenous (contain nitrogen) base
2 condensation reactions take place to make a nucleotide, so 2 water molecules are released

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5
Q

what are the five different organic bases?

A

A - adenine
T - thymine
C - cytosine
G - guanine
U - uracil

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6
Q

how are polynucleotides formed?

A

the phosphate group at the 5th carbon of the pentose sugar of one nucleotide forms a phosphodiester bond with the OH group at the 3rd carbon of the pentose sugar of an adjacent nucleotide
nucleotides link together through condensation reactions
forms a long, strong sugar-phosphate backbone

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7
Q

what is the model of the structure of DNA?

A

the double helix
two anti-parallel polynucleotide chains joined through hydrogen bonds
deoxyribose sugars and phosphate groups alternate
nitrogenous bases pair up using hydrogen bonds
the two strands coil into a double helix
proposed by watson and crick

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8
Q

what are the two types of nitrogenous base?

A

purines (bigger) - 2 ring base
adenine & guanine
pyrimidines (smaller) - 1 ring base
thymine & cytosine

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9
Q

what is complementary base pairing?

A

guanine pairs with cytosine using 3 hydrogen bonds
adenine pairs with thymine (or uracil in RNA) using two hydrogen bonds

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10
Q

what is chargaff‘s rule?

A

equal amounts of adenine and thymine must pair together
equal amounts of guanine and cytosine must pair together
a small pyrimidine base pairs to a larger purine base
results in a constant distance between the DNA backbone = anti-parallel polynucleotide chains

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11
Q

what is the function of mRNA?

A

short sections of DNA corresponding to a single gene are transcribed into short messenger RNA (mRNA) which are single-stranded
mRNA is small enough to leave the nucleus and go to the ribosome for protein synthesis
mRNA is a polymer composed of many nucleotide monomers (polynucleotide)

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12
Q

what are the three types of RNA?

A

ribosomal RNA (rRNA)
transfer RNA (tRNA)
messenger RNA (mRNA)

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13
Q

what is DNA replication?

A

copying & replicating of the DNA
during interphase of cell division
happens only in the nucleus
makes identical copies of DNA to form sister chromatids
double stranded - both strands are templates

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14
Q

what are chromosomes?

A

made up of a DNA double helix
humans have 23 pairs in their somatic cells (body cells)

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15
Q

what is semiconservative replication?

A

two new molecules of DNA are produced
each molecule consists of one old strand and one new strand
model proposed by watson and crick

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16
Q

what is the process of semiconservative DNA replication?

A

DNA unwinds by action of gyrase enzyme
strands separate by action of helicase enzyme which breaks the hydrogen bonds between complementary base pairs
free DNA nucleotides are attracted to and pair up with their complimentary bases
hydrogen bonds form between complementary base pairs
DNA polymerase makes the sugar phosphate backbone by forming phosphodiester bonds between nucleotides
2 identical copies of DNA made

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17
Q

what are replication errors?

A

sequences of bases are not always matched correctly
results in an incorrect sequence in the newly copied strand
errors are random and lead to mutations
daughter cells will not receive identical genetic information
proteins & new cells either do not function or are not made

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18
Q

what were the three main DNA replication models?

A

the conservative model
the semiconservative model
the dispersive model

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19
Q

what does the conservative replication model state?

A

two DNA molecules are produced
the original molecule is conserved and contains two old DNA strands
the new molecule is made of two new DNA strands

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20
Q

what did meselson and stahl do?

A

carried out a series of experiments to see which model was a better representation of DNA replication
used the fact that nitrogen was in the bases and that it has two isotopes

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21
Q

what was meselson and stahl’s experiment?

A

bacteria was grown on heavy nitrogen so all the DNA contained heavy nitrogen
bacteria was then transferred to light nitrogen
bacteria was left to grow on the light nitrogen for a set period of time (1, 2 & many generations)
DNA was extracted and spun it very fast in a centrifuge
DNA settled in the centrifuge tube at a point dependent on its density

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22
Q

what were the results of meselson and stahl’s experiment?

A

bacteria grown on heavy nitrogen = line of DNA at bottom of centrifuge tube
bacteria grown on light nitrogen = line of DNA at top of centrifuge tube
DNA molecule made of light & heavy DNA = lines of DNA in middle of centrifuge tube
the results proved that DNA replication was semi-conservative

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23
Q

what happened in meselson & stahls experiment after each of the 3 generations?

A

generation 1 = position of band inbetween heavy & light nitrogen - rules out conservative model generation 2 = new DNA band made with only light nitrogen - light strand of DNA must have been a template strand for the new molecule - rules out the dispersive model
generation 3 = highest band gets thicker as more of the DNA is made of only light nitrogen

24
Q

what is protein synthesis?

A

proteins are made in the nucleus and at ribosomes

25
what is a gene?
the sequence of nucleotide bases in DNA determines the sequence of amino acids in a polypeptide chain each chromosome has many genes
26
what are alleles?
a different form of the same gene can be recessive or dominant can be heterozygous or homozygous
27
what are the two parts of protein synthesis?
transcription and translation
28
what is transcription?
mRNA is made from DNA happens in the nucleus
29
why do we need transcription and mRNA?
DNA is too large to leave the nucleus DNA is transcribed (copied) into mRNA which can leave the nucleus through nuclear pores mRNA then attaches to the ribosome for translation
30
what is the process of transcription?
DNA unwinds in the region coding for a gene hydrogen bonds between DNA bases are broken so DNA strands separate bases of free RNA nucleotides form hydrogen bonds with complementary bases of DNA nucleotides making up the template strand on DNA RNA polymerase catalyses the formation of phosphodiester bonds between nucleotide bases forming the sugar phosphate backbone (A U and G C) an mRNA copy of coding strand separates from the template DNA strand as hydrogen bonds break it leaves the nucleus via nuclear pores the DNA double helix reforms
31
what is the sense strand?
the strand of DNA that contains the coded information runs from 5’ to 3’
32
what is the antisense strand?
complimentary copy of the sense strand acts as a template strand during transcription runs from 3’ to 5’
33
what is RNA polymerase?
forms phosphodiester bonds between RNA nucleotides to make mRNA forms a sugar-phosphate backbone
34
what is DNA polymerase?
makes the new strand in semiconservative DNA replication
35
what is translation?
makes a protein from mRNA happens at the ribosome
36
what is ribosomal RNA (rRNA)?
makes up the two subunits in ribosomes (along with proteins) the ribosome holds the mRNA in position while it is translated into a specific sequence of amino acids (a polypeptide)
37
what is transfer RNA (tRNA)?
composed of a strand of RNA folded so that at one end of the molecule there are 3 bases (the anticodon) the anticodon binds to a complimentary codon on mRNA this uses normal base pairing rules (A U and C G) forms a clover leaf structure, shorter than mRNA also has an amino acid binding site - brings the correct amino acid into the ribosome hydrogen bonds between base pairs and between codon & anticodon
38
what are the three stages of translation?
initiation elongation termination
39
what is the initiation stage of translation?
mRNA binds to the small subunit of the ribosome a tRNA with the complementary anticodon to the start codon comes into the ribosome and binds to the mRNA the tRNA is attached to a specific amino acid hydrogen bonds form between the codon & anticodon the large subunit of the ribosome now binds to the mRNA
40
what is the elongation stage of translation?
another tRNA with the anticodon complementary to the next codon is brought into the ribosome they are paired & bind together the tRNA will be attached to a specific amino acid a peptide bond forms between the two amino acids (condensation reaction) this is catalysed by peptidyl transferase the ribosome moves along the mRNA releasing the first tRNA, the amino acid stays bonded to the second amino acid the stages are repeated
41
what is the termination stage of translation?
when the ribosome reaches a stop codon translation is terminated the ribosome dissociates from the mRNA and the protein is released
42
what is the result of translation?
a very specific protein with a specific primary, secondary and tertiary structure
43
what is a genome?
entire DNA sequence of that particular organism
44
what is the genetic code?
each three nucleotides in a row count as a triplet & code for a single amino acid
45
what are the four key terms of the genetic code?
triplet code non-overlapping code degenerate code universal code
46
what is a triplet code?
three bases are needed to code for one amino acid there are 64 different triplets / codons one start codon & three stop codons
47
what is a non-overlapping code?
the sequence is read so that each base is only part of one codon / triplet
48
what is a degenerate code?
there is more than one codon for most amino acids significant because not all mutations in the DNA will lead to the wrong amino acid being put in a polypeptide chain
49
what is a universal code?
the code is the same in almost all living organisms the same specific base triplets code for the same amino acids
50
what is ATP?
used for energy transfer in all cells of all living organisms made as a result of respiration (aerobic & anaerobic)
51
what is the structure of ATP?
three phosphate groups bonded to the ribose sugar ribose sugar (pentose sugar like in RNA) adenine nitrogenous base (purine) adenine and ribose together make adenosine - ATP stands for adenosine triphosphate
52
why is ATP not a good long-term store of energy?
the phosphate bonds are not stable lipids and carbohydrates are better for this
53
what are the properties of ATP?
small - moves easily in, out & within cells water soluble - energy requiring processes take place in aqueous solution releases energy in small quantities easily regenerated by condensation reactions
54
how is a phosphate group removed from an ATP molecule?
hydrolysis reaction H2O & ATP hydrolyse enzyme used 30.6kJ energy released & ADP is made  the energy released can be coupled to energy-requiring reactions in the cell including: protein synthesis, active transport, endocytosis, exocytosis and muscle contraction
55
how is ADP made into ATP?
condensation reaction energy from respiration and photosynthesis is used to form ATP H2O is made ATP synthase enzyme used

Alevel biology (6 decks)

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