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Biology > Controlling Gene Expression > Flashcards

Controlling Gene Expression Flashcards

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1
Q

The Four stages of how gene expressions can be controlled

A
  • Transcriptional Control
  • Post Transcriptional Control
  • Translational Control
  • Post Translational Control
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2
Q

What happens in transcriptional control (Transcription Factors in Eukaryotes)

A
  • Transcription Factors bind with specific DNA sequences, the right complexes of transcription factors is required for transcription to begin
  • Increasing/ decreasing the production of transcription factors will control the transcription of other genes
  • RNA polymerase is not a transcription factor
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3
Q

What happens in transcription Control (Chromatin remodelling) (2)

A
  • DNA associates with histone proteins forming chromatin
  • DNA wraps around a bundle of 8 histones which is called a nucleosome
  • Methylation causes nucleosomes to pack tightly together = transcription factors cannot bind to DNA and gene cannot be expressed
  • Acetylation and Phosphorylation causes nucleosomes to be loosely packed and transcription can bind to DNA
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4
Q

What happens in transcriptional control (The Lac OPeron) (3)

A
  • Operon are a group of genes which are under control of a same regulatory mechanism. Composed of structural genes and control sites ( Promoter and Operator Regions)
  • Promotor is where RNA polymerase binds for transcription
  • Operator controls genes switching on or off, if nothing is bounded to operator RNA polymerase can bind to promotor. However if a repressor protein is bound to operator the binding site for RNA polymerase to bind with proctor is partially blocked
  • Structural Gene codes for protein
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5
Q

What is Down Regulation

A
  • The repressor Protein is constantly produced and binds to the operator. This will prevent RNA polymerase binding to DNA and beginning transcription.
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6
Q

What is the role of Cycle AMP

A
  • To up-regulate the rate of transcription to produce the required amount of enzymes to metabolise lactose.
  • By using a cAMP (secondary messenger)
  • If glucose levels are low = cAMP is produced and is attached to CAP, this binds DNA, CAP allows RNA polymerase to bind to promoter and transcription will occur
  • If glucose levels are high = cAMP is not made and CAP cannot be used to bind DNA. Transcription is at low levels
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7
Q

What is an operon

A
  • A group of genes which are under control of the same regulatory mechanism
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8
Q

What is operon composed of?

A
  • Structural genes and controlling regions
  • Controlling Regions (Promotor and Operator)
  • Promotor = RNA polymerase binds to this
  • Operator = Controls genes from switching on and off, if a repressor protein binds to it this will partially block the binding site for RNA polymerase
  • Structural genes codes for a protein
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9
Q

What are the enzymes that E.Coli synthesises for?

A
  • beta galactosidase which hydrolises lactose into glucose and galactose
  • beta galactose permease which takes up lactose
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10
Q

Examples of respiratory substrate of E.Coli

A
  • Glucose
  • Lactose
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11
Q

What is the function of Beta Galactosidase

A
  • Hydrolises Lactose into Glucose and Galactose
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12
Q

What is the function of Beta Lactose Permease

A

Enables the cell to take up lactose which is embedded on the cell membrane and creates a channel

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13
Q

Describe the events when lactose is the only respiratory substrate available

A
  • Lactose will passively enter the cell
  • Lactose will bind to the repressor protein, this causes the repressor to change shape and release from the operator
  • Structural gene can now be transcribed
  • Beta galactosidase and Beta lactose permease is formed
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14
Q

What happens in Post - transcriptional control

A
  • Intron is taken out of DNA to become pre mRNA
  • In the beginning, transcription produces a molecule called pre-mRNA to form mature RNA
  • Cap and tail are added, ‘splicing’ by spliceosomes which remove introns
  • RNA can be edited by ‘splicing’ (via sub,del or ins|) meaning a single strand of DNA produces strands of mRNA
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15
Q

How is splicing activated

A

Through cAMP which triggers a protein to be made to cause splicing

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16
Q

What does the cap do in post transcriptional control

A
  • Allows ribosomes to bind to mRNA better
  • Helps to stabilise mRNA and delay degradation in cytoplasm
17
Q

What happens in translational control if you don’t want it to occur

A
  • Switching translation on and off
  • If we don’t want translation to occur mechanisms can be:
  • mRNA degradation
  • binding of inhibitory proteins and this will stop mRNA binding to the ribosomes and synthesis of proteins
18
Q

What happens in translational control if you do want it to occur? ( phosphorylation and protein kinases)

A

-If we do want translation to occur the mechanism would be:
-Activation if initiation factors which will allow mRNA to bind to ribosomes.
- This is done by phosphorylation (adding a phosphate group to the protein will change the tertiary structure and function of the protein|)
- This chemical process is done by protein kinase which will catalyse this and is a regulator of cell activity.

19
Q

What happens in post-translational control?

A
  • Modifying the protein
  • Addition of non - protein groups like carbohydrate chains and lipids for cell signalling
  • Modify amino acids and formation of bonds such as disulphide bridges
  • Protein folding or shortening (changing structure)
  • Modification of cAMP e.g. lac operon cAMP binds to cAMP repressor protein to increase rate of transcription in repressor genes.
20
Q

What are homeobox genes?

A
  • Ancient, highly conserved regions of DNA found in animals, plants and fungi
  • 180 base pairs long
  • Codes for homeodomains = protein segments that act as transcription factors.
21
Q

Function of Homeobox genes

A
  • Able to switch genes on and off = regulatory proteins
  • They control the development of the body plan
22
Q

What are hox genes?

A
  • Are one specific group of homeobox genes only found in animals.
23
Q

What is a homeodomain?

A
  • part of the protein in homeobox genes which binds to DNA and switches other genes on and off.
24
Q

What are hox genes responsible for?

A
  • Are responsible for body positioning
  • The order in which the genes appear along the chromosomes is the order when their effects are expressed in the organism
25
Q

What are the types of symmetry

A
  • Radial Symmetry = Have no left or right sides but has a head and tail
  • Bilateral Symmetry = Have left side, right side, head and tail.
  • Asymmetry = Organisms that have no lunes of symmetry
26
Q

What is apoptosis

A
  • Programmed Cell Death
27
Q

How does apoptosis work?

A

Removing unwanted cells and tissues in order to shape organisms
Cells undergoing apoptosis will release chemical signals This can also trigger mitosis and proliferation to occur = remodelling of tissues.

28
Q

What is a mutation?

A

A random change in sequences of bases in DNA

29
Q

3 types of point mutation

A
  • Subsitution
  • Insertion
  • Deletion
30
Q

Effects of different mutations

A

Neutral = No effect on the phenotype of an organism due to normal functioning of protein

Beneficial = Rarely a protein is synthesised resulting in a new and useful characteristic in the phenotype

Harmful = Phenotype is affected in a negative way, proteins aren’t synthesised and cannot function properly.

31
Q

Effect of nucleotide if substitution happens

A

= If new codon codes for a different amino acid, this causes a change in the primary structure of protein
= However as codons are degenerative, the new codon may code for the same amino acid leading to no change

32
Q

Effect of nucleotide if insertion and deletion occur

A
  • This will cause a frame shift mutation
  • As triplet codes are non over-lapping and this is the reading frame of the sequence of bases
  • Every three bases codes for one amino acid
  • This will move/shift the reading frame and change every successive codon

Biology (8 decks)

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