Micro - organism Flashcards
Prokaryotes
unicellular entities
lack a nucleus and membrane bound organelles unlike eukaryotes
genetic material is usually in
the nucleoid region of the cytoplasm
some prokaryotes contain a single circular chromosome of double stranded DNA also known as a plasmid.
Examples of prokaryotes
Bacteria and Archaea
Prokaryotes reproduce
via binary fission
other processes such as
transduction, transformation, conjugation are forms of reproduction that also takes place in a prokaryote
Prokaryotic Cell Features
Capsule: polysaccharides that aid prokaryotes such as bacteria to adhere to surfaces and to each other also prevent desiccation of the microbe.
Cell wall: located below the capsule, maintains the cells shape and plays in a role protection and withstanding pressures within the cell.
Cell membrane: lies underneath the cell wall, containing phospholipids which are arranged in a bilayer conformation where the hydrophobic tails (fatty acids) are in the interior with the hydrophilic heads (glycerol plus phosphate) out on the exterior
Appendages: prokaryotic cells contain a few appendages which are protrusions on the cell surface such as fimbriae, pili and flagella. Fimbriae are thin filaments that aid adhesion. Pili are longer structures that play a role in conjugation and in some cases movement, whilst flagellum is a structure that helps the cell to move around.
Ribosome: the site of protein synthesis
Nucleoid region: region in the cell where the double stranded circular chromosomal materials are found.
Chromosome: genetic material found within the nucleoid region
Plasmid: small circular rings of extrachromosomal double stranded DNA which carry non-essential genes and are duplicated independent of chromosomes
Eukaryotes
Cells that possess a clearly defined nucleus, the nucleus has a membrane around it.
The nucleus holds chromosomes, and the cellular compartment holds organelles, some of which are membrane bound.
The membrane bound eukaryotic organelles are the nucleus, mitochondria, Golgi apparatus, lysosomes and endoplasmic reticulum
4 Main types of eukaryotes
animals
plants
fungi
protists
Eukaryotes reproduce
Some eukaryotes reproduce asexually whilst some reproduce sexually.
Eukaryotic Cell Features
Mitochondria: powerhouse of the cell, ATP is synthesized here
Lysosomes: contains enzymes that break down pathogens, old organelles etc.
Peroxisome: aids in metabolizing wastes
Endoplasmic reticulum: synthesizes, stores and transports lipids and carbohydrates
Golgi apparatus: area where proteins are modified
Nucleus: stores genetic material
Nucleolus: ribosomes are formed in this region
Cytoplasm: the area of the cell where the organelles are found
Differences Between Prokaryotes and Eukaryotes
- Genetic material is usually circular and
located in nucleoid region
Genetic material are linear chromosomes
situated in the nucleus - Lack organelles, small ribosomes
Contains a few organelles such as mitochondria, Golgi apparatus, large ribosomes - Usually unicellular, generation/growth time is fast
Can be multicellular, generation/growth
time is slow - Cell wall found in all
Cell wall only in plants and fungi
Binary fission
asexual reproduction that bacteria uses to divide creating 2 identical daughter cells
Conjugation
direct contact is used to transfer genetic material between bacteria
Transformation
exogenous DNA is transferred into host cells
Transduction
process by which viruses transfer genetic material between bacteria. This is performed by bacteriophage
Archaea
single-celled prokaryote whose cell wall lacks peptidoglycan, ether linked lipids are in their cell wall as opposed to ester linked lipids in bacteria
Phospholipid bilayer
vital component of a cell membrane made of a hydrophobic tail and hydrophilic heads
Viruses
small parasites that lack the capacity to undergo replication, transcription, or translation outside of a host cell. Viruses that infect bacteria are known as bacteriophages. Viruses lack the concept of homeostasis which is the capacity to regulate and sustain their internal environment. Almost all viruses rely on the host cell for translation, and to a certain extent for transcription and replication.
Viruses may contain
nucleic acid either
double stranded DNA or single stranded RNA surrounded by capsid (virus encoded protein coat). Viruses also have an outer membrane lipoprotein envelope which is obtained via the process of budding from the host cell.
Glycoprotein
found on the viral surface play a role in the structure of the virion as well as interact with receptors on the host cell.
Nucleocapsid
genome and the capsid together
Some RNA and DNA viruses contain
non- structural proteins which are integral for immediate transcription or replication after infection of the host cell
Virus Replication Strategies
Some viruses utilize the host cell machinery for replication.
Large DNA viruses with bigger genomes encode their own replication and transcription factors.
RNA viruses require RNA polymerase for transcription and these enzymes are not present in the host cell thus must be encoded by the virus.
Retroviruses are RNA viruses which utilize RNA-dependent DNA polymerase to replicate the RNA genome through a DNA intermediate (reverse transcription).
Viral Replication Cycle
- Attachment: virus binds to host cell surface receptors via its glycoproteins
- Viral entry: viral genome enters host cell after attachment.
- Synthesis: host cell machinery manufactures the viral proteins and copies viral nucleic acid.
- Assembly: new viruses are produced from viral components
- Release: newly synthesized viruses are released and may leave with a layer of the host cells surface which is the envelope layer
Oncoviruses
viruses linked with the development of cancer
can produce proteins that inhibit or deteriorate the function of tumour suppressor genes which are known to play a key role in cell division
inactivation of tumour suppressor genes, cells grow uncontrollably thus forming tumours
Cancer (human papillomavirus)
Cervical cancer is induced by oncogenic proteins produced by special types of human papillomavirus.
