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AS-level Biology Unit 1 > 1.5- Nucleic acids and their functions > Flashcards

1.5- Nucleic acids and their functions Flashcards

1
Q

What are the components of a nucleotide?

A

one or more phosphate group
pentose sugar
organic base

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2
Q

By what reaction do the components join to form a nucleotide?

A

condensation reaction

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3
Q

What is an example of a nucleotide?

A

adenosine triphosphate (ATP)

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4
Q

What does ATP consist of?

A

3 phosphate groups
ribose- pentose sugar
adenine- purine base

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5
Q

How are the bonds formed between phosphate groups in ATP?

A

condensation reaction

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6
Q

What is the enzyme that breaks down ATP?

A

ATPase

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7
Q

Where is ATP produced?

A

cytoplasm
mitochondria (matrix and inner membrane)
chloroplasts (thylakoid membranes)

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8
Q

What happens in order to release energy from ATP?

A

the enzyme ATPase breaks the bond between the middle and terminal phosphate group, which releases energy, to break the bond ,
water is added, therefore a hydrolysis reaction
adenosine diphosphate (ADP) and a phosphate group (Pi) are formed

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9
Q

What is the hydrolysis of ATP?

A

ATP + Water—–> ADP + Pi + Energy

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10
Q

What is Pi?

A

inorganic phosphate group

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11
Q

Is the hydrolysis of ATP reversible?

A

yes

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12
Q

How does ADP and Pi reform ATP?

A

energy is needed which comes from the breakdown of glucose during respiration or from photons of light exciting electrons during photosynthesis
Adding a phosphate group to ADP is called phosphorylation

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13
Q

How much energy is released or required in ATP hydrolysis and reverse?

A

30 kJ mol^-1

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14
Q

Wha is an exergonic reaction?

A

when energy is released

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15
Q

What is an endergonic?

A

when energy is required

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16
Q

What does ATP provide energy for?

A

metabolic processes
active transport
movement
nerve transmission
secretion

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17
Q

Why is ATP needed for metabolic processes?

A

to build larger complex molecules from smaller simpler molecules
e.g synthesis of DNA from nucleotides, polypeptides from amino acids

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18
Q

Why is ATP needed for active transport?

A

to change the shape of carrier proteins in cell membranes to allow molecules and ions to be transported against a concentration gradient

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19
Q

Why is ATP needed for movement?

A

for muscle contraction

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20
Q

Why is ATP needed for secretion?

A

the packaging and transport of secretory products int vesicles in cells

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21
Q

What are the advantages of ATP/ Why is it useful?

A

hydrolysis of ATP involves a single reaction that releases immediate energy whereas breakdown of glucose involves a number of intermediates and takes longer for the energy to be released
only one enzyme is needed to releases energy from ATP (ATPase), whereas many needed for glucose
ATP releases energy in small amounts when and where needed
ATP is soluble and easily transported

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22
Q

What are two types of nucleic acids?

A

deoxyribonucleic acid (DNA)
ribonucleic acid (RNA)

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23
Q

What do DNA nucleotides consist of?

A

deoxyribose- pentose sugar
adenine, thymine, cytosine, guanine- bases
phosphate group

24
Q

What do RNA nucleotides consist of?

A

ribose- pentose sugar
adenine, uracil, cytosine, guanine
phosphate group

25
Q

What are purine bases? Which are?

A

bases with a double ring structure
adenine and guanine

26
Q

What are pyrimidine bases? Which are?

A

bases with a single ring structure
cytosine, thymine, uracil

27
Q

What are the complimentary bases for adenine?

A

thymine or uracil

28
Q

How many bonds when adenine bonds with thymine or uracil?

A

2 hydrogen bonds

29
Q

How many bonds when cytosine bonds with guanine?

A

3 hydrogen bonds

30
Q

What is DNA?

A

double stranded polymer of nucleotides
the alternating phosphate groups and pentose sugars form the backbone of the polynucleotide
the pentose sugar in DNA is called deoxyribose
there are 4 different bases, each containing nitrogen- adenine, thymine, cytosine, guanine
Purine bases bond with pyrimidine bases by hydrogen bonding
adenine bonds with thymine, cytosine bonds with guanine, this is known as complimentary base pairing
base pairing links two polynucleotide chains which are antiparallel to each other
the molecule is twisted to form a double helix, this shape is maintained by hydrogen bonding

31
Q

What are the two functions of DNA?

A

replication
protein synthesis

32
Q

What is RNA?

A

single stranded polymer of nucleotides
contains the pentose sugar ribose
contains the organic bases adenine, guanine, cytosine, uracil
does not contain the base thymine
RNA is much shorter than DNA

33
Q

What are the types of RNA?

A

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

34
Q

What is mRNA?

A

long single stranded molecule
synthesised in the nucleus and carries the genetic code from the DNA to the ribosomes in the cytoplasm
each stand of mRNA contains the genetic code for one gene
each gene codes for a particular polypeptide

35
Q

What is rRNA?

A

found in the cytoplasm and is a component part of ribosomes
ribosomes are made of rRNA and protein and are synthesised in the nucleolus of the nucleus
ribosomes are the site of protein synthesis by a process called translation

36
Q

What is tRNA?

A

small single stranded molecule folded
each tRNA molecule has an amino acid attachment site CCA
at the opposite end of the tRNA molecule there is a triplet of bases called an anticodon
tRNA molecules transport amino acids to the ribosomes
the anticodon bases form a complex with complimentary bases on the mRNA molecule (codon)
this allows translation to take place

37
Q

How does DNA replication occur?

A

hydrogen bonds holding the base pairs together, break and two halves of the DNA molecule separate
DNA unwinds
as the DNA strands separate the enzyme DNA polymerase catalyses the addition of free nucleotides to the exposed bases, each chain acts as a template so that free nucleotides can be joined to their complimentary bases
this process results in two identical DNA molecules, each made up of one newly synthesised chain and one chain from the original molecule

38
Q

Who proposed the semi conservative hypothesis of DNA replication?

A

Meselson and Stahl

39
Q

What does meselson and stahl’s hypothesis suggest?

A

each DNA strand act as a template of new DNA
each new strand of DNA formed is composed of an original strand and a newly synthesised strand

40
Q

How did meselson and stahl prove their theory?

A

cultured E-coli for several generations on a medium containing amino acids made with the heavy isotope nitrogen 15
the bacteria incorporated the nitrogen 15 into their nucleotides

41
Q

What was mesleson and stahl’s experiment?

A

the scientists extracted the bacterial DNA and centrifuged it
the DNA settled at a low pint in the tube because it contained the heavy nitrogen 15 isotope
bacteria were washed, then transferred to a medium contains the normal lighter isotope nitrogen 14, and were allowed to replicate once
when extracts of DNA from the first generation culture were centrifuged, it was shown to have a midpoint density, half nitrogen 15 and half of the new nitrogen 14
when extracts of DNA were taken from the second generation, grown in a nitrogen 14 medium, the DNA settled at mid points and high points in the tube after centrifugation
this provided evidence which supported the semi-conservative hypothesis

42
Q

How many bases code for an amino acid?

A

3

43
Q

What are 3 bases called?

A

triplet code or codon

44
Q

What is transcription?

A

the synthesis of RNA from a DNA template where the code in the DNA is converted into a complementary RNA code

45
Q

When does transcription occur?

A

when free RNA nucleotides align themselves opposite complimentary nucleotides on the DNA strand

46
Q

How does transcription occur?

A

DNA unwinds and unzips at a particular region to be copied; this is catalysed by an enzyme called helicase, which break the hydrogen bonds between base pairs
The enzyme RNA polymerase attaches to the DNA at the beginning of the sequence to be copied.
Only one of the DNA strands acts as the template to be copied
RNA polymerase moves along the DNA forming bonds that add nucleotides one at a time to the RNA.
This results in the synthesis of the molecule mRNA alongside the unzipped portion of DNA.
Behind the RNA polymerase the DNA strands re-join to reform the double helix.
The mRNA carries the DNA code out of the nucleus through a nuclear pore to the cytoplasm and attaches itself to a ribosome

47
Q

What is translation?

A

process of making proteins by forming a specific sequence of amino acids based on coded instructions in mRNA

48
Q

How does translation occur?

A

mRNA contains the code for protein synthesis
begins when an mRNA molecule attaches itself to a ribosome- initiation
The ribosome acts as a framework moving along the mRNA, reading the code.
mRNA contains triplet codes or codons. Each codon codes for a different amino acid.
tRNA molecules attach to specific amino acid molecules and carry them to the mRNA molecule.

49
Q

What are complimentary anticodon?

A

codon bases align and are held together by the ribosome at an attachment site; a codon-anticodon complex is formed

50
Q

What is initiation?

A

a ribosome attaches to a start codon at one end of the mRNA molecule

51
Q

What is elongation?

A

two amino acids are close enough together for a peptide bond to form between them; a new amino acid is added to the polypeptide chain

52
Q

What is termination?

A

Amino acids are added until the ribosome reaches a stop codon
The ribosome detaches from the mRNA molecule and the polypeptide is released

53
Q

What happens once the tRNA is released from the ribosome?

A

it is free to collect another amino acid from the amino acid pool in the cytoplasm. Energy in the form of ATP is needed to attach the amino acid to the tRNA molecule; this is amino acid activation

54
Q

What are start and stop codons?

A

tell the ribosome where to start and stop reading the genetic code

55
Q

What is a polysome system?

A

a group of ribosomes moving along the same mRNA molecule, one after the other

56
Q

What does degenerate mean?

A

AS-level Biology Unit 1 (6 decks)

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