Chapter 19- genetics of living systems

mutation

Any change to the genetic material

3 types of point mutations

1. Substitutions

2. Deletions

3. Insertions

Substitution mutations

a base in the DNA sequence is changed by another base e.g. silent, missense and nonsense mutations

deletion mutations 

where a base in the DNA sequence is deleted and causes frame shift

insertion mutations 

When a base in the DNA sequence is added and causes a frame shift

Silent mutation

Base change codes for the same amino acid

Missense mutation

Change in base sequence causes different amino acid being encoded into a protein

nonsense mutation

mutation will code for a STOP codon

Four types of chromosomal mutations

1. Duplication

2. Deletion

3. Inversion

4. Translocation

Chromosomal duplication mutations

a whole gene/section of DNA is copied

Chromosomal deletion mutations

a whole gene/section of DNA is deleted

Chromosomal inversion mutation 

W whole generation/section of DNA is rotated around the centromere 

Chromosomal translocation mutation

a whole gene/section of DNA is swapped with a non-sister chromatid

Mutations can be:

1. Neutral

2. Beneficial

3. Harmful

Neutral mutations

effect the phenotype so have no impact on organism- may occur in introns which are removed from pre-mRNA before reaching ribosome 

Examples of beneficial mutations

1. Lactose tolerance- animals become intolerant to milk after weening→ milk provides fats and sugars so drinking it provides advantages

2. Trichromatic vision vs dichromatic→ tri have three cones on the retina to detect to provide better ability to distinguish food/poisonous berries, predators and other species

Examples of harmful mutations

cystic fibrosis, type 1 diabetes and cancer

What is lac operon and where does it occur?

Occurs in bacteria to produce a cluster of lactose genes 

5 regions on the lac operon

1. The code for repressive protein

2. Promoter region (were RNA polymerase binds)

3. Operator region (were repressor protein binds)

4. Code for galactosidase

5. Codes for lactose permease

Process of LacOperon

1. Repressor protein is made

2. Repressor protein binds to operator region

3. Repressor protein prevents RNA polymerase from binding to promoter region

4. Lactose binds to repressor protein

5. Repressor protein changes in shape and dissociates from operator region

6. RNA polymerase binds to promoter region and transcripts Lab Z (galactosidase) and Lac Y (lactose permease)

7. Galactosidase hydrolysis lactose into glucose

Transcription modification 

Icons can be removed, or reordered to change the mRNA that is translated, resulting in different proteins 

Translation modification

post-translation modification (PTMS) can modify the protein (occurs in Golgi apparatus)

What is DNA wound around

Histone proteins 

Euchromatin

chromatin during interphase- is unwound DNA in the nucleus, so justices are separated and gene can be transcribed

Acetylation

adding an acetylene group makes histone less positive so genes are switched on

What does it mean for genes to be switched on?

DNA is less coiled, allowing for more transcription

Methylation 

Adding a methyl group to make the histone protein more hydrophobic (wrap tighter around histone as doesn’t want to be associated with fluid) switching genes off 

What does it mean to switch genes off?

DNA coils tighter around the histone

consequences of renting genes on

1. Cancer e.g. breast

2. Alzheimer’s

3. Louis

4. Rheumatoid

Consequences of turning genes off

1. Cancer e.g. leukaemia, lymphomas

Epigenetics

The study of how environmental and behavioural factors can impact how genes function, without changing the DNA sequence

Transcription factors 

small proteins the regulate the transcription of a gene 

HOX genes

• Control the development of the body plan of organisms

• Aid in the development from a zygote to a complete organism (left-right/ head-tail)

• They are 180bp (homeotic sequence) and code for transcription factors that bind to the DNA and regulate the transcription by switching genes on and off

Apoptosis 

programmed cell death to help shape the body plan and development of organs e.g. separation of the skin between fingers and creating folds in the brain to form larger SA

Process of apoptosis

1. Stress initiates the apoptosis either environmental factors (mutation or infections) or HOX genes (genetic stress and forming body plan)

2. Enzymes break down the cytoskeleton

3. Cell contents are packaged into vesicles (blebs)

4. Vesicles are engulfed by phagocytes and destroyed

Factors affecting apopotosis and gene expression

• Homeotic (homeostasis) balance can influence the transcription of genes

• Stressed can upset balance e.g. external (light/temperature/pollution) or internal (hormonal/psychological stress)

• Drugs can influence HOX genes e.g. Thalidomine can be used too treat cancer as it prevents the gene that develops blood vessels