Unit 6.1- Cellular Control Flashcards
Types of point mutations:
- Silent mutations
- Nonsense mutations
- Missense mutations
Silent mutations:
- Change to the base triplet but the triplet codes for the same amino acid
- The primary structure, and therefore the tertiary structure, is not altered
Missense mutations:
- A change to the base triplet causes a different amino acid to be coded for
- Could have a significant effect on the protein produced
- The alteration to the primary structure leads to a change in the tertiary structure, altering its shape and preventing it from carrying out its usual function
Nonsense mutations:
- A mutation alters a base triplet so that it becomes a stop triplet
- Results in a truncated protein that will not function
- The protein will most likely be degraded in the cell
Types of indel mutations:
- Insertions and deletions
- Expanding triple nucleotide repeats
Insertions and deletions:
- Causes a frame shift (as long as bases are not inserted or deleted in multiples of three)
- All subsequent base triplets are altered
- The primary structure and therefore the tertiary structure of the protein is dramatically altered, meaning the protein cannot carry out its usual function
- If the protein is abnormal, it will be rapidly degraded in the cell
Expanding triple nuceotide repeats:
- Some genes contain a repeating triplet
- In expanding triple nucleotide repeats, the number of the repeated triplet increases at meiosis, and again from generation to generation
Exon definition:
The coding or expressed region of DNA
Intron definition:
The non-coding region of DNA
Operon definition:
A group of genes that function as a single transcription unit
Transcription factor definition:
Protein or short non-coding RNA that can combine with a specific site on a length of DNA and inhibit or activate transcription of a gene
What does E. coli metabolise if glucose is absent?
- Lactose if it is present
- Lactose induces the production of two enzymes:
- Lactose permease, which allows lactose to enter the bacterial cell
- Beta galactosidase, which hydrolyses lactose to glucose and galactose
What is the Lac operon?
- Length of DNA about 6000 base pairs long.
- Contains the following regions:
- Regulatory gene
- Promoter region (control site)
- Operator region (control site)
- LacZ (structural gene)
- LacY (structural gene)
What do lacZ and lacY code for?
- B galactosidase
- Lactose permease
How does the lac operon work in the absence of lactose (when there is glucose)?
- Regulatory gene I codes for repressor protein (lacI)
- Repressor protein binds to operator, preventing RNA polymerase from binding to the promoter region
- Repressor protein therefore prevents the genes LacZ and LacY from being transcribed
- The genes for lactose metabolism are not made
- The genes are ‘switched off’
How does the lac operon work in the absence of glucose and when there is lactose?
- Molecules of lactose bind to the LacI repressor protein, altering the shape of the LacI repressor, preventin git from binding to the operator.
- The RNA polymerase enzyme can then bind to the promotor region and begin trnascribing the structural genes into mRNA that will then be translated into the two enzymes.
- Thus, lactose induces the enzymes needed to break it down
How do transcription factors work?
They slide along a part of the DNA molecule, seeking and binding to their specific promoter regions. They may then aid or inhibit the attachment of RNA polymerase to the DNA, and activate or suppress transcription of the gene
What is primary mRNA?
mRNA where all the DNA of the gene has been transcribed, including the introns. The introns are then removed through splicing and the exons are joined together
Apoptosis definition:
Programmed cell death
Conserved definition:
Has remained in all descendant species throughout history
Homeobox sequence definition:
Sequence of 180 base pairs (excluding introns), found within genes that are involved in regulating patterns of anatomical development in animals, fungi and plants
Hox genes definition:
Subset of homeobox genes, found only in animals; involved in formation of anatomical features in correct locations of body plan
What is a homeodomain sequence?
- The 60 amino acids coded for by the 180 DNA base pairs in the homeobox sequence
- The homeodomain sequence can fold into a specific shape and bind to DNA, and regulate the transcription of adjacent genes
- Transcription factors
What shape do homeodomain-containing proteins fold into?
H-T-H (alpha helix, turn alpha helix)
What sequence of bases does part of the homeodomain amino acid sequence recognise?
TAAT (on the enhancer region of a gene that needs to be transcribed)
What are hox genes involved in in the development of an embryo?
- Expressed in order along the anterior-poterior axis of the developing embryo
- Sequential and temporal gene expression
How does apoptosis happen?
- Enzymes break down the cell cytoskeleton
- The cytoplasm becomes dense with tightly packed organelles
- Cell surface membrane changes and small protrusions called blebs form
- Chromatin condenses, nuclear envelope breaks and DNA breaks into fragments
- The cell breaks into vesicles that are ingested by phagocytis cells, so that cell debris does not damage any other cells or tissues
- The whole process happens quickly
