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Biology > D1.2: Protein Synthesis > Flashcards

D1.2: Protein Synthesis Flashcards

1
Q

Define transcription.

A

Process by which the genetic information encoded in DNA is copied into RNA (always occurs in the 3’ to 5’ direction)

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2
Q

List the roles of RNA polymerases in the process of transcription. ​​

A
  • RNA polymerase binds to antisense strand then separates DNA strands
  • RNA polymerase builds mRNA molecule on antisense strand as it moves from 3’ to 5’
  • RNA polymerase forms covalent bonds between the RNA nucleotides
  • RNA polymerase detaches from DNA molecule and the double helix forms
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3
Q

Explain the initiation stage in transcription

A
  • Initiation stage: RNA Polymerase binds to the DNA at the start codon separating the 2 strands of the DNA by breaking the H bonds, exposing the bases
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4
Q

Explain the elongation stage in transcription

A
  • Elongation stage: RNA Polymerase builds a mRNA molecule on an antisense DNA strand. RNA polymerase moves along DNA reading it; each time a base is read, a free RNA nucleotide is added to the growing mRNA
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5
Q

Explain the termination stage in transcription

A
  • Termination stage: A termination sequence in DNA is reached at the mRNA is released; RNA polymerase detaches from the DNA strand allowing the 2 strands to come together again
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6
Q

State the complementary base pairing utilized in transcription.

A

In DNA,
- A=T (2 H Bonds)
- C=G (3 H bonds)

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7
Q

Distinguish between the sense and antisense strands of DNA.

A

sense strand of DNA (coding):
- DNA strand that has the same sequence as the RNA molecule produced during transcription except T is replaced with U. Runs from 5’ to 3’.

antisense strand of DNA (template):
- DNA strand used as a template during transcription to synthesise a complementary RNA molecule. Runs from 3’ to 5’

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8
Q

Outline how stability of the information stored in DNA is maintained.

A
  • DNA is transcribed many times and for all the cells that do not go through regular cell divisions, DNA needs to remain intact throughout the life of the cell
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9
Q

Define gene expression.

A

The process by which genetic information is used to produce RNA and proteins.

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10
Q

Outline the major steps of gene expression.

A

Transcription:

Translation:

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11
Q

State what the importance of the pattern of gene expression is

A

It is how cells differentiate for specific functions.

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12
Q

Outline the role of transcription in regulating gene expression.​

A

pk

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13
Q

Define translation.

A

Process by which ribosomes use the genetic information carried by mRNA to synthesise proteins (always occurs in the 5’ to 3’ direction)

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14
Q

State the location of translation in cells.​

A

Ribosomes that are found either in the cytoplasm or attached to the rER

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15
Q

Outline the roles of mRNA, ribosomes and tRNA in translation.

A

mRNA:
- carries the genetic code that determines the order of amino acids in a polypeptide sequence

Ribosomes:
- catalyse the formation of peptide bonds

tRNA:
- responsible for transporting amino acids to the ribosome according to the mRNA sequence

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16
Q

Explain the central dogma of molecular biology theory

A
  • DNA is the master set of instructions for all cell activities
  • RNA is a temporary photocopy of specific genetic instruction (gene)
  • Proteins are the products created from these instructions that carry out the cellular functions

DNA–>RNA–>Protein

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17
Q

Describe the structures of mRNA and tRNA.

A

mRNA:
- linear structure

tRNA:
- L shaped structure

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18
Q

Describe the structure of the ribosomes, including the small and large subunits and the names and roles of the tRNA binding sites.

A

contains a large subunit with 3 binding sites for tRNA molecules to bind to (only 2 can bind at a time), contains a small subunit which mRNA binds to

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19
Q

Explain the process of Translation (MR CAT APP)

A

MR: Messenger RNA binds to the Ribosome (via the small subunit)

CAT: Codons (on mRNA) are recognised by complementary Anticodons on Transfer RNA

APP: Amino acids are joined by the ribosome via Peptide bonds to form Polypeptides

tRNA loop forms a hydrogen bond with mRNA

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20
Q

What is a DNA strand whose base sequence does not change over time said to be?

A

Conserved

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21
Q

State the complementary base pairing utilized in translation.

A

DNA:
- Adenine pairs with Thymine
- Cytosine pairs with Guanine

RNA:
- Adenine pairs with Uracil
- Cytosine pairs with Guanine

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22
Q

Define codon and anticodon.

A

Codon:
- A set of three adjacent nucleotides in DNA or mRNA that code for a particular amino acid.

Anticodon:
- A sequence of three nucleotides in tRNA that is complementary to a specific codon in mRNA, allowing the tRNA to recognise and bind to the corresponding codon.

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23
Q

Describe the formation of hydrogen bonds between codon and anticodon.

A
  • anticodon loop of the tRNA molecule aligns with the corresponding codon on the mRNA strand
  • this is stabilised by specific hydrogen bonds between the complementary bases (A-U and G-C in RNA),
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24
Q

Explain the reason that a sequence of three nucleotides is required to code for the 20 amino acids commonly utilized by organisms.

A
  • 1 nucleotide = 1 of the 4 bases
  • 1 codon = contains 3 nucleotides = 1 amino acid
  • 4^3 = 64 (where 4 consists of 4 different bases and 3 is the number of positions within a codon) different combinations of 64 codons.
  • ANS: 64 sequences of 3 nucleotides, a codon, can code for all 20 amino acids used to build proteins in protein synthesis. This provides 64 different combinations to encode for all amino acids
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25
Q

Define codon, degenerate and universal as related to the genetic code.

A

Codon:
- A set of three adjacent nucleotides in DNA or mRNA that code for a particular amino acid.

Degenerate:
- multiple codons to code for the same amino acid.

Universal:
- genetic code is nearly identical in all organisms, with most codons specifying the same amino acids.

26
Q

Use a genetic code table to determine the amino acid sequence coded for by a given DNA or RNA sequence.

A

pk

27
Q

Outline the process of translation elongation, including codon recognition, bond formation and translocation.

A
  1. tRNA molecule carrying an amino acid pair with next free codon via A site
  2. Ribosome covalently attaches the amino acid on a tRNA molecule at P site to the tRNA molecule at A site via peptide bond catalysed by ribosome due to a condensation reaction occurring
  3. Ribosome translates along mRNA by 1 codon. Deacylated tRNA molecule moves to E site and exits ribosome. tRNA molecule carrying polypeptide in A site moves to P site.
  4. Process repeats until polypeptide is complete and when ribosome reaches any termination codon where the component disassembles.
28
Q

Define gene mutation.

A

A gene mutation is a change in the nucleotide sequence of a section of DNA / RNA.

29
Q

State the cause of sickle cell anemia, including the differences in the HbA and HbS alleles.

A

a single point mutation in the gene responsible for producing one of the polypeptides in haemoglobin

30
Q

State the difference in RNA sequences in the transcription of the HbA and HbS alleles.

A
31
Q

State the difference in amino acid sequences in the translation of the HbA and HbS alleles.

A
32
Q

Outline the consequences of the HbS mutation on the structure and function of the hemoglobin protein.

A

Consequence on structure of hemoglobin protein:
- DNA and mRNA sequence changes due to substitution mutation = Forms insoluble fibrous strands

Consequence on function of hemoglobin protein:
- Insoluble Hemoglobin cannot carry O2 as effectively resulting in reduced O2 supply to tissues

33
Q

Discuss the symptoms of sickle cell disease.

A
  • sickle cells destroyed more quickly than normal cells = low rbc count (anaemia)
  • sickle cells may form clots in capillaries = blocked blood supply to vital organs
34
Q

Identify the 5’ ends and 3’ ends of a strand of RNA.

A
35
Q

Describe the formation of the covalent bond between adjacent nucleotides during transcription.

A

Phosphodiester bond forms between the 3’ end of one RNA Nucleotide and the 5’ end of the next nucleotide

36
Q

State where the RNA polymerases can add the 5’ phosphate of a free nucleotide to

A

The RNA polymerases can only add the 5’ phosphate of a free nucleotide to the 3’ ribose of the elongating strand.​

37
Q

State the direction of movement of the ribosome along the mRNA molecule.

A

Ribosome moves from the 5’ to the 3’ direction as the codons on mRNA molecule are read

38
Q

Outline the structure and function of the promoter regions of DNA.

A

Structure:
- As it is a non-coding region, it contains no bases

Functions:
- contains specific sequences that allow RNA polymerase and transcription factors to bind to initiate transcription

39
Q

Describe the initiation of transcription, including the role of the promoter sequence, transcription factors and RNA polymerase.

A

Transcription Initiation:
- RNA polymerase binds at promoter region (non-coding region) on the template strand
- Transcription factors (repressors / activators) bind to the promoter region
- Transcription begins

40
Q

Compare the function of activator and repressor sequences within the promoter.

A

Activator sequences:
- Consists of proteins that bind to enhancer sites and function to increase transcription rates

Repressor sequences:
- Consists of proteins that bind to silencer sites and function to decrease transcription rates

41
Q

State what transcription factors are

A

Transcription factors are proteins that bind to the promoter.

42
Q

State the 2 possible functions of transcription factors

A

Some transcription factors activate transcription (activator proteins) while others inhibit transcription (repressor proteins)

43
Q

Define “coding” and “non-coding” sequences of DNA.

A

coding sequences of DNA:
- DNA sequences within the genome that contain the info required to synthesise proteins (DNA bases directly correspond to amino acid sequence in a protein)

non-coding sequences of DNA:
- DNA sequences within genome that do not consist of the info to make a protein (DNA bases are never represented within the amino acid sequence)

44
Q

Outline five functions of noncoding DNA sequences found in genomes.

A

Regulators of gene expression
- DNA sequences that regulate gene expression in diff ways; promoters act as a binding point for RNA polymerase to catalyse transcription

Introns
- DNA sequences that get removed at the end of transcription

Telomeres
- Repetitive sequences that protect ends of chromosome to ensure DNA is replicated correctly

Genes for tRNA & rRNA
- they code for RNA molecules that don’t get translated into proteins but instead fold to form tRNA molecules / rRNA molecules that form part of the structure of ribosomes

45
Q

Outline the location and timing of post-transcriptional modification of RNA.

A
  1. pre-mRNA gets synthesised during transcription
  2. 5’ cap and a poly-A-tail gets added which protect the mRNA molecule from degradation
  3. Splicing occurs which removes the introns (as they are non-coding sequences) and join the exons to form mature mRNA

This occurs before translation in the ribosomes found in the cytoplasm but after transcription in the nucleus of eukaryotic cells

46
Q

Describe the function of the 5’ cap

A

5’ cap:
- A modified guanine nucleotide added to the 5’ end of pre-mRNA during post-transcriptional modification, providing stability and assisting in mRNA processing and transport.

47
Q

Describe the function of the poly-A tail.

A

poly-A-tail:
-Multiple adenine nucleotides added to the 3’ end of a mRNA transcript to protect and stabilise the molecule.

48
Q

State what pre-mRNA is

A

The initial RNA molecule transcribed from DNA, which contains both introns and exons.

49
Q

Compare intron and exon sequences of genes.

A

intron (INTRUDING SEQUENCES):
- Introns are DNA sequences that contain no coding information but sometimes contain controlling sequences that regulate transcription of the gene

exons (EXPRESSING SEQUENCES):
- Exons are the DNA sequences that code for a polypeptide.

50
Q

Outline the process of RNA splicing. ​

A
  1. snRNP forms base pair with ends of introns
  2. spliceosome and looped intron forms
  3. Intron is excised (removed)
  4. Exons are ligated (joined); Spliceosome disassembles
51
Q

Describe the process of alternative RNA splicing.

A
  • this involves the removal of exons
  • results in different polypeptide from a single gene sequence
52
Q

Outline the benefit of alternative RNA splicing.​

A
  • allows for production of multiple proteins from a single gene
  • this is done by modifying the sequence of exons included in the mature mRNA.
53
Q

Outline the process of translation initiation.​

A
  • 5’ end of mRNA binds to small ribosomal subunit
  • Ribosome moves along mRNA (from 5’ to 3’) until start codon AUG is recognised
  • Initiator tRNA (only used to begin translation) binds to codon AUG of mRNA due to complimentary base pairing of anticodon UAC
  • Large ribosomal subunit binds to complete assembly of translation complex. Translation starts!
54
Q

List types of modifications of polypeptides that may be required to form a functional protein.

A
  • formation of disulphide bridges between cysteine residues
  • Conjugation with other proteins
  • Chemical modifications to improve structural stability
  • Removal of amino acids from polypeptide chain
55
Q

Outline the two stages of modification of preproinsulin to form functional insulin.​

A

Preproinsulin to Proinsulin:
- a signal peptide is removed in rER

Proinsulin to Mature insulin:
- As proinsulin folds within Golgi complex, opposite ends of the protein are linked by disulfide bridges and the intervening segment C peptide is removed

Mature insulin forms

56
Q

List reasons when proteins typically exist for a relatively short time within a cell.

A

Proteins degraded by proteins if they are:
- Damaged
- Unneeded

They are then recycled

57
Q

Outline the function of proteasomes in the recycling of amino acids.

A
  • hydrolyses proteins by breaking peptide bonds betw amino acids
  • This allows cells to maintain a supply of amino acids + rids any non-functional amino acids
58
Q

State the name of the bond holding tRNA and amino acids together

A

Ester bond

59
Q

State what is used specifically in DNA profiling to make non-coding regions useful

A

Tandem repeats (sequence of two or more DNA bases that is repeated)

60
Q

State the correct directions of Translation, Transcription and DNA Replication

A

From 5’ to 3’

61
Q

State which process facilitates the production of insulin from pre-proinsulin.

A

Proteolysis

62
Q
A

Biology (20 decks)

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