Topic 7: Microbial Genetics Flashcards
Define Genetics
Genetics: Study of what genes are, how they carry information, how it is expressed, and how genes are replicated
Genome:
All of the genetic material in a cell (Chromosomes + mitiochondria/chloroplasts and/ or plasmids).
Genomics: molecular study of genomes.
Chromosome: Structure that carries hereditary information, contains many genes. Can be circular (bacterial) or linear (human).
Gene: Genetic makeup of an organism e.g. all the genes.
Phenotype: External manifestation of genotype or expression of genes (e.g. blue eyes is a phenotype).
Chromosome and Gene
- Chromosome is subdivided into genes, the fundamental unit of heredity responsible for a given trait.
- Site on the chromosome that provides information for a certain cell function.
- Segment of DNA that contains the necessary code to make a protein or RNA molecule (ie functional products)
- Three basic categories of genes:
1. Genes that code for proteins - structural genes
2. Genes that code for RNA
3. Genes that control gene expression - regulatory genes.
Genotype and Phenotype
Genotype: All the genes in a genome constitute the genetic makeup.
Phenotype: Expression of genotype creates observable traits
Genome Vary in Size
- Smallest viruses 4 to 5 genes
- E. coli - single chromosome containing 4,288 genes; 1mm; 1,000 times longer than cell.
- Human cell- 46 chromosomes containing 31,000 genes; 2 metres; 180,000 - times longer than the cell.
Eukaryote Chromosome
- Multiple and linear
- Diploid
Prokaryote Chromosome E. Coli
- Single, circular chromosome
- Looped and folded
- Attaches at one or several places to cell membrane
- E.coli chromosome 4.2Mb
- Bacterial Chromosomes are usually 3-4Mb (3000-4000kb) in size.
- Haploid
Define Chromosome
- Chromosome
1. Double stranded, closed circular
2. Composed of many genes
3. All different lengths and directions
-Gene
1. Encodes a protein or RNA (or carries a function)
2. Can be almost any length, but average 1,000bp
(bp= base pairs).
- DNA
1. Deoxyribonucleic acid double helix
2. Anti-parallel right-hand helix - Nucleotides
1. A,T,G or C = base + deoxyriboe + Pi
DNA - Deoxyribonucleic Acid
- Two strands twisted into a helix
- Basic unit of DNA structure is a nucleotide
- Each nucleotide consists of 3 parts
1. 5 carbon sugar: 2 deoxyribose (5 carbon sugar).
2. Phosphate group
3. Nitrogenous group: Adenine, guanine, thymine, cytosine. - Nucleotides covalently bond to form a sugar - phosphate linkage - the backbone.
- each sugar phosphate attaches to two phosphates
- 5 carbon and 3 carbon
- Strands are held together by hydrogen bonds between AT and CG.
- Phosphates (negative charge) on outside of double helix.
DNA Replication
- DNA is copied by DNA polymerase
- In the 5’- 3’ direction
- Leading strand is synthesised continuously
- Lagging strand is synthesised discontinuously
- Initiated by an RNA primer
- Okazaki fragments
- RNA primers are removed and Okazaki fragments joined by a DNA polymerase and DNA ligase.
- DNA replication is semiconservative where each chromosome end up with one new strand and one old strand.
RNA- Ribonucleic acid
- Ribose sugar and phosphate backbone
- 4 nucleotides
1. Uracil (U) instead of Thymine (T)
2. Adenine (A)
3. Cytosine (C)
4. Guanine (G) - 3 main types of RNA in the cell
1. mRNA - Messenger RNA
2. tRNA - Transfer RNA
3. rRNA - Ribosomal RNA
Transcription
- DNA is transcribed to make RNA (mRNA, tRNA, and rRNA).
- Transcription begins when RNA polymerase binds to the promotor sequence
- Transcription proceeds in the 5’-3’ direction
- Transcription stops when it reaches the terminator sequence.
Translation
-mRNA is translated in codons (three nucleotides)
-Translation of mRNA begins at the start codon: AUG (AWAY YOU GO)
-Translation ends at a stop codon: UAA, UAG, UGA.
(U ARE ARRESTED; U ARE GROUNDED, U GOT ARRESTED)
