Katrina Chung

Pathology

Medicine Semester 1

Learning outcome Define gene, chromosome, genome, terms used in

gene alteration processes

Describe plasmid and its importance with relevant examples

Describe the mechanisms of bacteria genetic alteration and evaluate the consequences giving examples

List factors that influence genetic change

Definition (1)

Gene

Segment of DNA that encodes for a specific polypeptide/protein

- structural proteins, enzymes

Heritable

Chromosome

Main DNA material of a cell that contains the genes

Thread-like structure

Definition (2)

Genome

Total collection of genetic material in the cell

- includes chromosome and extrachromosomal material

Determines ALL properties and hereditary information of a bacterial cell

Plasmids (1)

Small, circular double-stranded (ds) DNA

- linear in some species of bacteria

Extra-chromosomal

Replicate independently of host chromosome

Heritable

(http://sandwalk.blogspot.com)

Plasmids (2)

Transferrable through

- conjugation

- transformation

- transduction

Non-essential for normal existence of bacteria cell

Confer additional properties

- resistance to antibiotics

- increase virulence

Plasmids (3)

Examples

- F plasmid

- R plasmid

- bacteriosin plasmid

- plasmids associated with pathogenicity

Gene alteration (1)

DNA replication normally produces identical genes in all daughter cells

Error in replication

- result in altered gene

- encode an altered protein

- possible altered structure or function

Gene alteration (2)

Consequences of altered gene

Altered structure or function essential for existence of cell

- cell may die

Altered structure or function non-essential

- cell may function as normal

- has less advantage

- may confer additional properties for better survival

Gene alteration (3)

Processes of gene alteration

Mutation

Recombination

Transformation

Conjugation

Transduction

Gene transfer

Gene alteration: mutation (1)

Spontaneous genetic processes

Chromosome composition altered during DNA replication

Results

- minimal: point mutations

- extensive: multisite mutations

Gene alteration: mutation (2)

Types of mutation

- point mutations

changes in single nucleotide

insertions, substitution, deletions

- frame-shift mutation

reading frame altered further in gene

could result in totally different protein