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Molecules > Molecular Biology 3+4 > Flashcards

Molecular Biology 3+4 Flashcards

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1
Q

Through what does mRNA have to exit to be exported from the nucleus and into the membrane?

A

Nuclear pore

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2
Q

What are three types of gene mutation?

A

1- Deletion/nonsense
2- Insertion/frameshift
3- Substitution/missense

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3
Q

What is deletion?

A

1- Base pair is deleted

2- Leads to frameshift or nonsense

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4
Q

What is insertion?

A

1- New base pair is inserted

2- Leads to frameshift or nonsense

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5
Q

What is substitution?

A

1- Base pair is substituted or replaced with a different base pair
2- Missense
3- AA replaced

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6
Q

What is polymorphism?

A

1- Minor change in sequence
2- Usually SNP (single nucleotide polymorphism)
3- Present in more than 1% of population
4- Main cause of genetic variation

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7
Q

What are the base pairs of the start codon?

A

1- AUG

2- Methionine (Met)

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8
Q

What is the role of tRNA?

A

1- ‘Adaptor’
2- Carries amino acids which correspond to mRNA sequence
3- Anti-codon, binds to codon of mRNA

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9
Q

Describe the structure of tRNA.

A

1- 80 nucleotides long
2- Clover leaf-like structure
3- Anti-codon present at the end which corresponds to mRNA codon

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10
Q

How does the right amino acid get added to the right tRNA?

A

1- 20 different amino acids
2- 20 different aminoacyl-tRNA synthesases
3- Each synthesase corresponds only to one amino acid and its compatible/cognate tRNAs
4- Amino acid is activated via enzymes and ATP
5- Amino-acyl is added to tRNA

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11
Q

How is the amino acid activated and transferred?

A

1- Activation:
Enzyme + AA + ATP –(Mg++)–> enzyme(aminoacyl-AMP) + PPi
2- Transfer:
tRNA + enzyme(aminoacyl-AMP) —-> aminoacyl-tRNA + enzyme

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12
Q

Compare eukaryote and prokaryote ribosomes.

A

1- Eukaryote: 80s
small subunit is 40s, large subunit is 60s
2- Prokaryote: 70s
small subunit is 30s, large subunit is 50s

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13
Q

How many binding sites do ribosomes have?

A

1- Four binding sites
2- One for mRNA
3- Three for tRNAs

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14
Q

What are the three phases of translation?

A

1- Initiation
2- Elongation
3- Termination

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15
Q

Describe the structure of a nuclear pore

A

A ring of subunits with a nuclear basket connected by nuclear fibrils

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16
Q

Where can ribosomes be found?

A

Free in cytoplasm or found attached to the endoplasmic reticulum

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17
Q

What is the difference between base pairs in DNA from RNA?

A

1- DNA has thymine

2- RNA has uraccil

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18
Q

What are the main differences in structure between DNA and RNA?

A

1- DNA is a double helix
2- RNA is a single strand
3- RNA may have secondary or tertiary structure

19
Q

What is the function of DNA?

A

Information storage

20
Q

What are the functions of RNA?

A
  • mRNA: genetic messenger
    2- tRNA: adaptor, physical link between mRNA and amino acids
    3- gRNA: guide RNAs for RNA editing
    4- Structural RNA: e.g. Xist, helps inactivate X chromosome
    5- Catalysts: rRNA links amino acids together, snRNAs help with DNA splicing
21
Q

What are promoters?

A

1- Region of DNA
2- Found before transcription site, signals its beginning
3- 100-200 bases long

22
Q

What are terminators?

A

1- Region of DNA

2- Marks the end of transcription

23
Q

What are the three different types of RNA polymerases?

A

1- RNA pol I
2- RNA pol II
3- RNA pol III

24
Q

What RNA does RNA pol I generate?

A

rRNA

25
Q

What RNA does RNA pol II generate?

A

Protein coding RNA

26
Q

What RNA does RNA pol III generate?

A

tRNA

27
Q

What is the TATA box?

A

1- Promoter sequence
2- Facilitates binding of RNA pol II
3- Facilitates binding of transcription factors such a TBP (TATA binding factor)
4- It is located 25 bases upstream of the starter code
5- TBP distorts shape of DNA once bound which allows binding of RNA pol II

28
Q

How does RNA polymerase bind to DNA and why?

A

1- RNA polymerase binds to the factor-promoter complex
2- Trans-acting factors bind to cis-acting promoter
3- RNA cannot bind directly to promoter

29
Q

What are enhancers?

A

1- Short DNA sequences
2- 50-1500 base pairs
3- Are not always located close to the transcription start site as they can work from a distance
4- Bind to transcription factors to increase likelihood of a specific section of DNA being transcripted
5- Opposed by silencers

30
Q

What opposes enhancers?

A

Silencers

31
Q

What are the two domains of transcription factors?

A

1- DNA binding domain

2- Activation domain

32
Q

What are six ways in which transcription can be controlled?

A

1- Protein is only synthesised when transcription needs to be carried out
2- Protein is inactivated by phosphorylation
3- Protein is inactivated by dephosphorylation
4- Protein is inactivated by ligand binding
5- Protein is inhibited and rendered inactive by an inhibitor
6- Protein has an inactive binding partner which is switched with an active binding partner when transcription needs to be carried out

33
Q

Why must mRNA be processed?

A

1- To protect from exonucleases
2- To aid their export from the nucleus
3- So it can be identified as mRNA

34
Q

What are exonucleases?

A

Enzymes which cleave nucleotides

35
Q

What are introns?

A

A segment of DNA or RNA which does not code for genes

36
Q

What are exons?

A

A segment of DNA or RNA which codes for genes after introns are spliced

37
Q

What are the steps of transcription?

A

1- DNA is unwinded by helicase
2- Genes are transcribed into pre mRNA
3- Intorns are removed by RNA splicing, producing mRNA
4- mRNA is exported from the nucleus into the cytoplasm

38
Q

What are the steps of RNA splicing?

A

1- Splicesome carrying RNAse and snRNA base pairs to the end of intron
2- Intron is spliced at its 5’ end
3- 5’ end of intron pairs with the downstream branch sequence, forming a lariat
4- The two exons are then ligated together

39
Q

What is Frasier’s syndrome?

A

1- Genetic mutation
2- Autosomal-dominant
3- Mutation of intron site leading to absence of three amino acids

40
Q

What is the importance of post-transcriptional modifications?

A

Many different proteins can be made from the same DNA

41
Q

How can DNA be unwound?

A

Through histone-modifying complex or

Chromatin remodelling complex

42
Q

What causes aniridia?

A

A defect in the eye caused by a genetic mutation of the transcription factor PAX6

43
Q

What are the symptoms of aniridia?

A

Cornea opaque

Iris absent

Retina degenerate

Lens opaque

Increased pressure

Molecules (4 decks)

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