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BIOCHEMISTRY SEM1 > DNA > Flashcards

DNA Flashcards

1
Q

What is the main role of DNA?

A

To provide the instructions for protein construction.

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2
Q

What does DNA stand for?

A

Deoxyribonucleic acid

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3
Q

What was Levene’s ‘Tetranucleotide Hypothesis’?

A

The idea that the amounts of the 4 bases were the same in all DNA molecules, regardless what organism.

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4
Q

What was Griffith’s transforming principle?

A

Looked at two different strains of pneumonia: S strain (virulant) and R strain (non virulent) and found that when injecting a mouse with dead S strain and live R strain, living S strain still killed the mouse. This was due to bacterial transformation.

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5
Q

The Avery–MacLeod–McCarty principle was..?

A

That DNA is the transforming principle as when treating Dead pneumonia S strain with DNase, RNase and protease and then adding to live R strain, the only sample that didn’t bacterial transform was the DNase treated R strain. Shows that DNA carries the genetic material as it was destroyed by DNase and no S strain was present as DNA wasnt present.

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6
Q

What did Hersey-Chase prove?

A

That DNA is the hereditary material by T2 bacteriophage.
They radioactively labelled the protein coat of phages and infected a bacterial cell and no radioactivity was found in cell.
They then radioactively labelled the DNA of the phages and infected a bacterial cell and radioactivity was found in the cell, this shows that DNA is passed into the cell along with hereditary genetic material.

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7
Q

What was Chargraff’s rules?

A

That A=T and C=G. 1:1 ratio base pair rule.
DNA is species-specific as DNA composition varies in many species.
He also came up with paper chromatography of nucleic acids.

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8
Q

What did Pauling discover and believe?

A

The structure of proteins, he believed that hereditary info was held in protein not DNA.

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9
Q

What did Rosalind Franklin discover?

A

The structure of DNA using radio crystallography, provided evidence for: the helix, double strands, nitrogenous bases and one turn every base pairs.

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10
Q

What did Watson and Crick do?

A

Came up with a 3D model of DNA and decided it was a helical structure, this opened doors for DNA understanding.

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11
Q

What is the structure of a nucleotide?

A

A deoxyribose 5-carbon sugar, a nitrogenous base (A,T,C,G) which is bonded to 1’ carbon of sugar and a phosphate group which is bonded to 5’ carbon sugar.

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12
Q

What replaces thymine base and deoxyribose sugar in RNA?

A

Uracil base and ribose sugar.

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13
Q

What does DNA polymerase catalyse?

A

The formation of phosphodiester bonds between the free 3’-OH group of a nucleotide and the alpha-phosphate of the new nucleotide.

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14
Q

What is the main characteristic of the phosphate backbone?

A

The strands have a 5’ and a 3’ end direction. They are reverse complimentary and are anti-parallel.

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15
Q

What bonds are between the complementary base pairs?

A

Hydrogen bonds.
There are two between A and T
There are three between C and G

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16
Q

What are the purines?

A

A and G - they have two organic rings

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17
Q

What are the pyrimidines?

A

C and T - they have one organic ring

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18
Q

What are the benefits of the strands being reverse complimentary?

A

It holds stability and there is a 2nd strand for errors

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19
Q

What are the main functions of DNA?

A
  • Storage molecule
  • Genes are transcribed into mRNA to then be translated into proteins.
  • ~1.6% of human genome protein coding .
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20
Q

What is chromatin?

A

A complex of macromolecules found in cells containing DNA and proteins

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21
Q

What is a gene?

A

The basic unit of hereditary in an organism, a small part of DNA that codes for one specific protein.

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22
Q

What are a few types of protein that can be produced?

A

Enzymes, globular, membrane and fibrous

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23
Q

What is the point of pre-mRNA?

A

To allow for introns to be removed via splicing so that RNA processing can occur and the protein coding sequence can be determined.

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24
Q

What are introns?

A

Non-coding sections of pre-mRNA transcript.

25
Q

What is the main 2 points of transcription?

A
  • The synthesis of RNA under DNA direction

- Production of messenger RNA (mRNA)

26
Q

What are the 2 main points of translation?

A
  • The synthesis of a polypeptide which occurs under the direction of mRNA.
  • Occurs in the ribosome
27
Q

What is the main event of transcription (genetic code)?

A

The gene determines the sequence of bases along the length of an mRNA molecule.
Genetic information is encoded as a sequence of non-overlapping base triplets, or codons that code for amino acids.
E.g. TAG would base pair: AUC

28
Q

What does the genetic code being universal mean?

A

That it’s shared by all organisms and genes transferred from one species to another can be turned into proteins (Genetic engineering and gene editing)

29
Q

What allows for amino acids to be different?

A

Their R group.

30
Q

What joins amino acids together to create a polypeptide chain?

A

Peptide bonds

31
Q

What catalyses RNA synthesis in transcription?

A

RNA polymerase

32
Q

What is the role of RNA polymerase?

A

To unzip the DNA to allow for a template strand and hook the RNA nucleotides together to form the mRNA strand.

33
Q

What are the three main stages of transcription?

A
  1. Initiation
  2. Elongation
  3. Termination
34
Q

What is the initiation (transcription) stage?

A

RNA polymerase binds to a promoter region on the DNA. This tells the enzyme where to start transcribing, which strand to transcribe and the direction in which to start it. The promoter aims the enzyme at the correct template strand.

35
Q

Where does transcription occur?

A

In the nucleus

36
Q

What is the elongation stage (transcription)?

A

When the RNA polymerase unwinds the DNA about 10 base pairs per time, it reads the template strand in a 3’ to 5’ direction. The enzyme then adds new nucleotides complementary to the bases on the 3’end of the building up strand.

37
Q

What is a major difference between DNA and RNA polymerase?

A

Unlike DNA, RNA polymerase does not proofread the RNA transcript and errors occur very commonly, however, as there are many copies made it’s not as harmful as mutations in DNA.

38
Q

What is the termination phase (transcription)?

A

The RNA polymerase reaches a termination sequence on the DNA template strand, the newly formed transcript releases itself from the DNA strand. An pre-mRNA strand is now present.

39
Q

How does pre-mRNA become mRNA?

A

Splicing of introns that do not code for proteins.

40
Q

What is post-transcriptional processing?

A

Modifications to the pre-mRNA in specific ways before it is dispatched to the cytoplasm e.g. splicing.

41
Q

What is the 5’ cap?

A

A guanine nucleotide connected to mRNA via an unusual 5′ to 5′ triphosphate linkage.

42
Q

What are the four main functions of the 5’ cap?

A
  • Promote translation
  • Prevent degradation from exonucleases
  • Regulation of nuclear export
  • Promotes 5’ proximal intron excision
43
Q

What is the 3’ polyA tail?

A

Multiple adenosine monophosphates

44
Q

What are the two main functions of the 3’ polyA tail?

A
  • Protects mRNA from enzyme degradation in the cytoplasm

- Aids in transcription termination

45
Q

What are the major two components needed for translation?

A
  • tRNA (transfer RNA)

- ribosome

46
Q

Why are tRNA molecules not all identical?

A

They carry specific amino acids and an anticodon (sequence of three nucleotides)

47
Q

What are the main functions of ribosomes during translation?

A
  • To allow specific recognition of tRNA anticodons with mRNA codons to allow protein synthesis
  • Ribosomal subunits are made up of ribosomal RNA.
48
Q

What are the three binding sites for tRNA in the ribosome and what order do they function?

A
  • A site (binding site)
  • P site (binding site)
  • E site (exit site)
49
Q

What is the initiation stage? (translation)

A

Initiation complex is formed whereby a tRNA molecule forms hydrogen bonds between its anticodon and the start codon (AUG) on the mRNA molecule. Initiation factors attach and join ribosomal units.

50
Q

What is the elongation stage? (translation)

A

The next tRNA molecule enters the A binding site where its anticodon binds with the mRNA codon, the amino acid forms a peptide bond with the amino acid in the P site. This is so the amino acid can join the growing polypeptide chain. The tRNA in the P site is transferred to the E site and released as the amino acid has been created.

51
Q

What is the termination stage? (translation)

A

The elongation stages are stopped by a stop codon (UAA, UAG or UGA) - they do not bind with tRNA or code amino acids. They bind a protein release factor which allows hydrolysis of the bond between the polypeptide chain and tRNA in the P site.

52
Q

How may proteins be modified post translation?

A
  • Glycolysation
  • Targeting
  • Folding
53
Q

What are the secondary structures of proteins held together by?

A

Hydrogen bonds between C=O and N-H groups of peptide bonds

They can be alpha helix or beta pleated sheets

54
Q

What are the tertiary structures of proteins held together by?

A

Disulphide bridges between cysteines, and ionic bonds between charged side groups

55
Q

How do proteins enhance their function by being made up of monomers of amino acids?

A

Allow the transition from a one-dimensional world to a third one by folding up in different ways to form functioning proteins.

56
Q

How do proteins enhance their function by having a wide range of functional groups?

A

Allow for an array of protein function such as enzymes. Chemical reactivity will affect how enzymes function.

57
Q

How do proteins enhance their function by having a spectrum of rigidness or flexibility?

A

Allows for an array of function such as rigidness being suitable for structure in exoskeletons and limited flexibility to act as hinges or springs.

58
Q

What happens when there is small changes in a shape of a protein?

A

Devastating effects such as: denaturation where the proteins structure is altered that much that it becomes dysfunctional

BIOCHEMISTRY SEM1 (4 decks)

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