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MCB > MCB2 - The Central Dogma Of Biology > Flashcards

MCB2 - The Central Dogma Of Biology Flashcards

1
Q

Discuss outside of DNA double helix.

A

Sugar phosphate backbone consisting of deoxyribose sugar and phosphate groups. Negatively charged due to phosphate.

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2
Q

Discuss core of double helix structure.

A

Nitrogenous bases which are perpendicular to the sugar phosphate backbone. Bases stack on top of one another contributing to the stability.

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3
Q

Define purine and pyrimidine bases.

A

Purine bases have 2 rings. Pyrimidine bases have 1 ring.

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4
Q

Give two types of grooves on DNA double helix and where they are.

A

Major groove - larger area.

Minor groove - smaller area.

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5
Q

Which nitrogenous bases bond to each other and how.

A

Cytosine and guanine bond with 3 hydrogen bonds.

Adenine and thymine bond with 2 hydrogen bonds.

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6
Q

Which bases are purines and which are pyrimidines.

A

Adenine and guanine are purines.

Thymine and cytosine are pyrimidines.

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7
Q

Where do transcription factors bind to on a DNA double helix.

A

Major groove.

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8
Q

Define the central dogma of biology.

A

Two step process by which information in genes flows into proteins through RNA.
DNA -> RNA -> proteins

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9
Q

Define DNA replication.

A

Process by which copy of DNA molecule is made.

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10
Q

Define transcription.

A

Copying of one DNA strand into complementary RNA by RNA polymerase.

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11
Q

Define translation.

A

Sequence of nucleotides in mRNA translated into amino acid sequence.

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12
Q

Give evidence contradicting the central dogma.

A

Retroviruses. Viruses composed of RNA contains reverse transcriptase enzyme which makes DNA from RNA.

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13
Q

Difference between nucleoside and nucleotide.

A

Nucleoside - nitrogenous base + sugar

Nucleotide - nitrogenous base + sugar + phosphate

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14
Q

Discuss differences between DNA and RNA.

A

DNA double stranded, RNA single stranded.
DNA contains thymine, RNA contains uracil.
DNA found only in nucleus, RNA found in nucleus and cytoplasm.

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15
Q

Discuss similarities between DNA and RNA.

A

Both contain genetic information. Contain 4 nitrogenous bases. Found in nucleus. Contains sugars and phosphates.

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16
Q

Define a nucleosome.

A

Histone proteins wrapped with DNA.

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17
Q

Give four histone proteins and how they form dimers.

A

Histone protein H2A and H2B.
Histone protein H3 and H4.
Dimer formed through extensive hydrophobic interactions.

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18
Q

How do histone proteins form an octomer.

A

4 histone dimers form an octomer.

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19
Q

Which histone protein clamps nucleosomes.

A

Histone protein H1 or H5.

20
Q

Discuss structure of DNA and how it becomes packaged.

A

Beads on a string formation. Compacts into solenoid structure. Forms 700nm structure. Becomes further compacted into chromosome.

21
Q

Define epigenetics.

A

Change in gene expression maintained through cell division and not involving a change in DNA sequence.

22
Q

Give three epigenetic mechanisms.

A

DNA methylation. Histone modifications. Non-coding RNAs.

23
Q

How are genes switched on and off.

A

Switched on - open and accessible DNA structure

Switched off - condensed, highly packaged DNA structure

24
Q

Where and how does DNA methylation occur.

A

Covalent addition of methyl group to 5th carbon of cytosine followed by guanine. Uses DNA methyl transferase enzymes (DNMTs).

25
Q

What effect does DNA methylation have and how does it occur.

A

DNA methylation causes gene expression to be switched off. Prevents transcription machinery from binding to gene. Also causes DNA methylation readers, containing DNA methyl binding domains (MBDs), recognise methylated CpG, causing downstream effects.

26
Q

How does DNA methylation become reversed and what effect does it have.

A

TET proteins, which are DNA methyl erases, oxidase methylated CpG, removing methyl group. Allows transcription machinery to bind meaning gene is “switched on”.

27
Q

What is the promote region on a gene.

A

Region where transcription machinery can bind - transcription factors, RNA polymerase.

28
Q

What are exons and introns.

A

Exons are DNA nucleotide sequences that are coding. Introns are non coding DNA.

29
Q

Discuss how histone modifications affect gene expression.

A

Post translational modifications on N terminal tails which are present on each histone proteins.

30
Q

Give two main types of histone medication.

A

Trimethylation and acetylation.

31
Q

Give examples of histone modifications on histone protein H3 and how it affects gene expression.

A

Trimethylation on lysine 9 - gene silencing as heterochromatin is formed.
Trimethylation on lysine 4 and acetylation on lysine 9 - gene expression.
Trimethaylation of lysine 27 - gene silencing due to Polycomb repressive complex.

32
Q

Which enzymes add and remove methyl from histone N terminal tails.

A

Histone methyltransferases.

Histone demethylases.

33
Q

Which enzymes add and remove acetyl groups on histone N terminal tails.

A

Histone acetyltransferases.

Histone deacetylases.

34
Q

Name other enzymes involved in N terminal modifications.

A

Kinases. Phosphatases. Ubiquitinases.

35
Q

Give examples of non coding RNA,

A 
snRNA - splicing 
rRNA - ribosomes
tRNA - translation 
miRNA - micro 
lncRNA - long non coding
36
Q

What are miRNAs

A

Micro RNA which regulate gene expression by acting post transcription (after production of mRNA)

37
Q

Discuss process of how miRNA acts.

A

RNA polymerase II forms primary miRNA (double stranded hairpin structure).
Primary miRNA recognised by DGCR8 protein.
DROSHA enzyme associates with DGCR8 forming micro-processor complex.
Primary miRNA cut into precursor miRNA.
Exported out of nucleus by protein EXPORTIN 5.
RNase protein DICER recognises pre-cursor miRNA and cleaves it.
Argonaute protein AGO 2 associates with RNA causing it to unwind and releases one strand.
Non released strand, guide strand, alongside AGO 2, associates with other proteins forming RISC - RNA induced silencing complex.
RISC translocated to complementary mRNA and silences it.

38
Q

How do RISCs affect gene expression.

A

Silence mRNA so reduces gene expression. Cuts mRNA preventing translation or prevents ribosome subunits from binding to mRNA for translation.

39
Q

Which miRNA mechanism is most common in plants.

A

Rapid mRNA degradation.

40
Q

Which miRNA mechanism is most common in humans.

A

Rapid translational repression with eventual degradation of mRNA.

41
Q

Role of ubiquitinases.

A

Add ubiquitin to proteins marking them for protein death. Move to proteases for degradation.

42
Q

Define and discuss RNAi.

A

RNA interference.

Natural defence mechanism in many species which is directed against foreign RNA molecules.

43
Q

Define lncRNA.

A

Long non coding RNA. Longer than 200 nucleotides. Found in nucleus or cytosol and can affect gene expression through different mechanisms.

44
Q

Give three ways in which lncRNAs act.

A

Act as scaffold bring proteins together and change chromatin model aiding/preventing gene expression.
Brings specific proteins to DNA/RNA through complementary base pairing aiding/preventing gene expression.
Act either cis or trans.

45
Q

Discuss differences between cis and trans action of lncRNAs.

A

Cis - controls transcription of genes on same chromosome.

Trans - controls transcription of genes on other chromosomes.

46
Q

Discuss histone acetylation In detail.

A

Lysine residue on histone tail becomes acetylated by HATs. Removal of positive charge. Reduced attach with negative charge DNA molecule. Acetylcholine group can be removed by HDACs.

47
Q

Discuss role of ATP dependent remodelling complexes.

A

ATP dependent remodelling complexes use ATP as an energy source to slide nucleosomes which can affect gene expression

MCB (13 decks)

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