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A-Level Biology > 2.1.3 > Flashcards

2.1.3 Flashcards

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1
Q

Two types of nuclei acids

A

DNA and RNA

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2
Q

How are nuclei acids created?

A

By many nucleotides (monomers) linked together in a chain

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3
Q

What elements do nuclei acids contain?

A

Carbon, hydrogen, oxygen, nitrogen and phosphorous

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4
Q

3 components of a nucleotide

A 
Pentode monosaccharide (sugar) containing 5 carbon atoms
PO42- (phosphate group) - inorganic molecule
Nitrogenous base - containing 1 or 2 carbon rings in it’s structure
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5
Q

How are nucleotides linked together?

A

Through condensation reactions (to form a polymer called a polynucleotide) - the phosphate group at the 5th carbon of the pentose sugar (CH2) forms a covalent bond with the hydroxyl group at the third carbon of an adjacent nucleotide - PHOSPHODIESTER BOND

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6
Q

What do phosphodiester bonds create and how can they be broken?

A

They form a long, strong sugar phosphate ‘backbone’ with a base attached to each sugar - they can be broken by a hydrolysis reaction by adding in water and releasing the individual nucleotides

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7
Q

Difference between the sugar in DNA and RNA?

A

Deoxyribose in DNA (one fewer oxygen atom than in Ribose)

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8
Q

How many different nucleotides are there?

A

4 - 4 different bases

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9
Q

Pyrimidines?

A

Thymine and Cytosine (smaller bases with the single ring carbon structures) - ALSO URACIL

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10
Q

Purines

A

Larger bases which contain double carbon ring structures - Adenine and Guanine

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11
Q

How many bonds do thymine and adenine form?

A

2 hydrogen bonds - 1 purine and 1 pyramidine

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12
Q

How many bonds do cytosine and guanine create?

A

3 hydrogen bonds

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13
Q

What is DNA made of?

A

2 strands of polynucleotides (with phosphodiester bonds for backbone and hydrogen bonds between bases) coiled into a double helix
These two strands are held together by hydrogen bonds between the bases

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14
Q

Describe structure of DNA

A

Each strand has a phosphate group (5’) at one end at a hydroxyl group (3’) at the other ; the two parallel strands are arranged so that they run in opposite directions therefore they are ANTIPARALLEL

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15
Q

Why are DNA strands anti parallel?

A

To allow complementary base pairing, crating hydrogen bonds and a structurally more stable molecule of DNA

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16
Q

What is complementary base pairing?

A

Adenine and thymine are able to form 2 hydrogen bonds and always join together and cytosine and guanine form 3 hydrogen bonds and also bind to each other

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17
Q

Why is there a constant distance between the sugar phosphate backbones?

A

Because a smaller pyrimidine base always binds to a larger purine base

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18
Q

What does complementary base pairing mean?

A

DNA a,ways has equal amounts of adenine and thymine and equal amounts of cytosine and guanine

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19
Q

What carries the genetic information of an organism?

A

The SEQUENCE of bases along a DNA strand

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20
Q

What is RNA and why is it important?

A

It transfers genetic material from the DNA to produce proteins (like enzymes etc) and this is passed on from generation to generation ; BUT because DNA is a very long molecule, it is unable to leave the nucleus in order to supply the sites of protein synthesis

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21
Q

How to get around problem of DNA being too large?

A

Relatively short section of the DNA molecule (a gene) is transcribed into short mRNA and each individual mRNA is therefore much shorter than the whole chromosome of DNA

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22
Q

What is Uracil?

A

It’s a base in RNA which replaces THYMINE - therefore it is a pyrimidine

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23
Q

How is DNA different from RNA?

A

DNA has deoxyribose sugar while RNA has ribose sugar

Thymine is replaced by uracil which forms 2 hydrogen bonds with adenine ; therefore base pairing rules still apply

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24
Q

Where do RNA polymers travel to?

A

Ribosomes - for protein synthesis (translation)

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25
Q

How can DNA be extracted from plant material?

A

Break down cell walls by crushing in pestle and mortar
Mix sample with detergent which breaks down cell membrane (releasing cell contents into solution)
Add salt - breaks hydrogen bonds between DNA and water
Protease enzyme will break down histone proteins in nuclei
Add a layer of ethanol causing precipitation to top of solution - DNA seen as white strand between alcohol and solution

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26
Q

When is DNA replication required?

A

When cells divide to produce more cells - these daughter cells are genetically identical therefore the two strands of DNA separate and each strand acts a template for the creation of a new DNA molecule with complementary base pairing ensuring that the two new strands are identical to the original - DNA REPLICATION

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27
Q

Summary of semi conservative replication

A

Double helix structure unwinds - hydrogen bonds holding together bases are broken and free nucleotides pair up with their complementary bases. Hydrogen bonds form between them too and then the new nucleotides join to their adjacent nucleotides with phosphodiester bonds

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28
Q

Why is it called semi conservative replication?

A

2 new double stranded DNA molecules are produced with each one consisting of one old DNA strand and one new strand therefore semi-conservative (half the same) replication

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29
Q

What does DNA helicase do?

A

Unwinds and separates the two strands - travels along the DNA backbone and catalysed the reactions that break the hydrogen bonds between complementary bases (UNZIPPING)

30
Q

What does DNA polymerase do?

A

Free nucleotides pair with newly exposed bases on the template strands and while this is happening, DNA polymerase catalysed the formation of phosphodiester bonds between adjacent nucleotides

31
Q

What does it mean by activated nucleotides?

A

These are free nucleotides that are attracted to their complementary bases after DNA helicase unzips them - MUST BE ACTIVATED

32
Q

DNA Ligase role?

A

DNA helicase unzips the strands in only one direction - DNA polymerase can only catalyse the formation of phosphodiester bonds in one direction (5’ to 3’ of GROWING STRAND) - 3’ to 5’ of ORIGINAL STRAND. For one strand this is fine BUT for the other strand it will be going in the opposite direction. Therefore DNA POLYMERASE FORMS THE OTHER STRAND AS A SERIES OF SHORTER STRANDS/FRAGMENTS (OKAZAKI FRAGMENTS - must follow 3’ to 5’ of original strand). THEREFORE DNA LIGASE MUST JOIN TOGETHER THE OKAZAKI FRAGMENTS - ONE STRAND IS CONTINUOUS (LEADING STRAND) WHILE THE OTHER IS DISCONTINUOUS (LAGGING STRAND)

33
Q

Difference between an activated nucleotide?

A

They have 3 phosphate groups instead of 1 - this is because when the condensation reaction of DNA polymerase is occurring (catalysing formation of phosphodiester bond), 2 of these phosphate groups leave PROVIDING THE ENERGY for the reaction to take place

34
Q

What is a mutation?

A

A random and spontaneous change in the sequence of DNA bases in the newly copied strand

35
Q

What is the genetic code?

A

DNA must code for a sequence of amino acids to form proteins - DNA carries the blueprints needed to synthesise the many different proteins needed by these organisms

36
Q

How is genetic code arranged in DNA?

A

The instructions are contained in the sequence of bases along the chain of nucleotides that make up the two strands of DNA - the codes are a simple triplet code and is a sequence of 3 bases (called a codon) ; each codon codes for an amino acid

37
Q

What codes for a gene?

A

A sequence of DNA that contains the complete sequence of bases/codons to code for an entire protein is called a gene

38
Q

What does it mean by genetic code being universal?

A

All organisms use this code - although the sequences of bases coding for each individual protein will be different

39
Q

How many different codons are possible?

A

64 different base triplets (4^3 = 64)

40
Q

What are the “must have codons”?

A

Start codon - at the beginning of a gene ; signalling the start of a sequence that codes for a protein
Stop codons - 3 of these that do not code for amino acids and signal the end of the sequence

41
Q

Why is it important to have a start codon?

A

Ensures that all the other codons are read in frame - so that they are non-overlapping

42
Q

What does it mean by degenerate?

A

There are only 20 regular amino acids and as there are 64 codons, several codons can code for the same amino acid ; therefore the code is degenerate ; ALLOWS FOR MORE THAN ONE CODON TO CODE FOR AN AMINO ACID - thus reduce the impact of a random mutation (typically only differ by 1 nucleotide)

43
Q

If the start codon is in the middle of a gene what does it code for? (ATG)

A

Methionine

44
Q

Where is DNA in the cell?

A

DNA is contained within the double membrane nuclear envelope which protects it from being damaged in the cytoplasm - protein synthesis s occurs at ribosomes in cytoplasm by chromosomal DNA is too large to leave he nucleus to supply the coding information needed

45
Q

How to get past problem of DNA being too large?

A

Base sequences of genes have to be copied and transported to the ribosome and this is called transcription which produces shorter molecules of RNA

46
Q

How does the DNA unzip during transcription?

A

Only section that contains the gene unwinds and unzips under DNA helicase (beginning at start codon)

47
Q

Sense and Antisense strand?

A

The sense strand contains the code for the protein to be synthesises and it runs from 5’ to 3’ ; the other strand is complementary and is called the antisense strand (3’ to 5’). THIS ANTISENSE STRAND IS THE TEMPLATE STRAND DURING TRANSCRIPTION ALLOWING RNA STRAND TO BE FORMED WITH SAME SEQUENCE OF BASES AS SENSE STRAND

48
Q

What happens when the DNA unzips during transcription?

A

Free RNA nucleotides base pair with complementary bases exposed on the antisense strand when it unzips ; thymine replaced by Uracil which binds to adenine on antisense strand. RNA polymerase forms phosphodiester bonds between RNA nucleotides and transcription stops at the end of the Gene creating mRNA ; it has same base sequence as sense strand except uracil
MRNA DETACHES AND LEAVES THROUGH A NUCLEAR PORE AND TRAVELS TO A RIBOSOME IN THE CYTOPLASM FOR TRANSLATION
DNA DOUBLE HELIX REFORMS

49
Q

Structure of ribosomes?

A

2 subunits in prokaryotes (1 large and 1 small) and each subunit with an equal amount of protein and a form of ribosomal RNA which is important in maintaining the structural stability of the protein synthesis sequence and plays a biochemical role in catalysing the reaction

50
Q

What does mRNA bind to during translation?

A

First binds to a specific site on the small subunit of a ribosome which holds mRNA in position while it is decoded into a sequences of amino acids

51
Q

Structure of tRNA?

A

Strand of RNA folded in such a way that three bases (called the anticodon) are at one end of the molecule. This anticodon will bind to a complementary codon on mRNA and the tRNA molecules carry an amino acid corresponding to that codon

52
Q

Role of tRNA?

A

Anticodons bind to complementary codons on mRNA and the amino acids are brought together in the correct sequence to form the primary structure of the protein coded for by the mRNA

53
Q

How does translation occur?

A

Amino acids are added one at a time with the polypeptide chain growing - ribosome act as the binding site for mRNA and tRNA and catalyse the assembly of the protein

54
Q

Summary of translation

A

1) mRNA binds to the small subunit of the ribosome at the start codon (AUG - correct one)
2) tRNA with complementary anticodon binds to the start codon carrying methionine
3) this continues with the next codons - max of two tRNAs can be bound on at the same time
4) amino acids are joined by formation of peptide bonds catalysed by the enzyme peptidyl transferase (rRNA)
5) ribosome continues down the mRNA molecule releasing each tRNA one at a time

55
Q

What happens when the ribosome reaches the end of the mRNA molecule (stop codon)?

A

Polypeptide is released

56
Q

What occurs while the amino acids are joined into their primary structure?

A

They fold into tertiary and secondary structures - this folding and the bonds formed are determined by the sequence of amino acids in primary structure

57
Q

Where does protein go to undergo further modification?

A

Golgi apparatus - becomes fully functional and carries out specific role after that

58
Q

Special about ribosomes?

A

They can follow on the mRNA behind the first creating multiple identical polypeptides simultaneously

59
Q

What processes require energy?

A

Muscle contraction, cell division, transmission of nerve impulses

60
Q

3 main types of energy requiring activity

A

Synthesis (large molecules like proteins)
Transport (sodium potassium pump - active transport for example)
Movement (protein fibres in muscle cells)

61
Q

Structure of ATP

A

It is a nucleotide - nitrogenous base (always adenine), pentose ribose sugar (as in RNA). 3 phosphate groups

62
Q

What is ATP known as?

A

Universal energy currency since it is used for the energy transfer in all cells

63
Q

What happens when bonds are broken?

A

Energy is needed

64
Q

What happens when bonds are formed?

A

Energy is released

65
Q

How does ATP release energy?

A

A small amount of energy is required to break the weak bond holding together the last phosphate group BUT a large amount of energy is released when the liberated phosphate undergoes other reactions involving bond formation (30.6 kJ)

66
Q

How is phosphate removed from ATP?

A

Through hydrolysis reaction - water is involved

67
Q

Equation for hydrolysis of ATP?

A

ATP + H2O -> ADP + Inorganic Phosphate + energy

68
Q

Why is ATP not as good a long term store as fats and carbohydrates?

A

Due to the instability of phosphate bonds in ATP - very immediate transfer of energy

69
Q

What is phosphorylation?

A

Energy released as a result of cellular respiration is used to reattach a phosphate group to an ADP molecule, creating ATP (which can then be again broken down to release energy) - as water is removed in phosphorylation, it is a condensation reaction

70
Q

Why is ATP a good immediate energy store?

A

ATP is rapidly reformed by phosphorylation therefore this inter conversion of ATP and ADP is happening all the time in living cells so cells do NOT need a large store of ATP

71
Q

Properties of ATP?

A

Small - moves easily into and out of cells
Water soluble - cytoplasm is aqueous for example
Contains bonds between phosphates with intermediate energy - large enough to be useful for cellular reactions but not so large that they are wasted as heat
Release energy in small quantities - suitabek to most cellular needs so energy is not wasted as heat
Easily recharged - can be recharged with energy (phosphorylation of ADP)

A-Level Biology (37 decks)

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