MCAT Biology

Viruses Microbiology Genetics Nervous System Cardiovascular Endocrine Lymphatic Muscle Bones Respiratory Reproductive

Virus

Virus

An intracellular parasite consisting of a capsid with a nucleic acid genome inside, unable to have both DNA and RNA.

Basic Virus Steps

attachment(adsorption) - specific attachment but not infected yet; and injection - penetration - from bacterium to host

Lytic Cycle

The process involving transcription and translation of viral genome, replication, and lysis of the host cell.

Hydrolase

In the lytic cycle, the virus will destroy the host genome and replicate its own DNA in it’s place

Lysogenic Cycle

Integration of viral genome into the host cell genome - combines its own genome with the host genome - divides into daughter cells with the new genomes when under stress

Transduction

Insert new genes/DNA that was not there before

Lytic Cycle of the Lysogenic cycle

The cell will undergo the lytic cycle if it is under stress → pH, temperature change, salinity → will duplicate since host is under stress

Productive cycle

Similar to the lytic cycle, but there is no lysis of the cell - doesn’t destroy the cell so it uses budding

Budding only works on

Animal cells - no cell wall there

Prions

Self-replicating proteins that do not follow the central dogma, lacking DNA/RNA, membranes, and organelles.

Viroids

Circular RNA molecules without a capsid, requiring co-infection, and blocking translation.

Making Viroids - two ways

Two different mechanisms make viroids -

• one by taking negative RNA, translating it to positive RNA to form many +RNA to form viroid copies

• One by taking -RNA and wrap +RNA to form a viroid copy

Bacteria Shapes

Round (coccus), rod (bacilli), spiral (spirillum), with flagella or cilia for movement.

Bacteria Cell Wall(+/-)

Gram-positive (stain dark, easier to penetrate) - two layers and gram-negative (stain light, harder to penetrate) bacteria - 3 layers

Bacteria Oxygen Use

Obligate aerobe - need, facultative anaerobe - can, tolerant anaerobe - doesn’t, and obligate anaerobe - dies based on oxygen requirements.

Energy Types of Use

• Photoauto = uses light and makes it on its own

• Chemoauto = use chemicals by self

• Photohetero = carnivorous plants

• Chemohetero = need other energy sources

Bacteria Reproduction

Binary fission for duplication, following an exponential growth pattern.

Conjugation

Genetic diversity mechanism in bacteria involving horizontal gene transfer through direct contact.

• F- is the donor(male) and F+ is the female recipient - gives an F plasmid, not a genome