MCAT Milesdown Biology

Nuceloid Region

DNA region in prokaryotes

• Bacteria DO NOT have nucleus!!

Nucleolus

Makes ribosomes, sits in the nucleus, no membrane

• recall ribosomes are important for synthesizing 1º proteins from amino acids

• both eukaryotes and prokaryotes have ribosomes —> necessary for cell function

Peroxisomes

Collect and break down material

• waste products & toxins

Rough ER

Accepts mRNA to make proteins

• rough bc studded w/ ribosomes

Smooth ER

Detox & makes lipids

Golgi apparatus

Modify/distribute proteins (only in eukaryotes)

• packaging system of the cell

COPI & COPII

• vesicles are used to transport materials and proteins to different parts of the cell, to know where they are going they need specialized coats

• Coat protein complexes: I & II go in different directions

• Both COPII & COPI operate on the cis face of the Golgi (the side facing the ER)

COPII:

• ER —> Gogli (Anterograde)

• delivers newly made proteins for processing and packaging

COPI:

• Golgi —> ER (Retrograde)

• returns mistakenly sent proteins or recycle machinery

Cathrin

another coat protein — but handles endocytosis and trafficking from the Golgi to lysosomes or the membrane

• moves between the gogli and the plasma membrane

• destination: Lysosome (via endosomes) or inside cell

• key function: handles endocytosis and Golgi sorting

Centrioles

9 groups of microtubules, pull chromosomes apart

• two centrioles are stacked at a right angle to form a centrosome —> on polar ends of the cell and pull chromosomes apart during anaphase

Lysosomes

• demo & recycling center

• made by golgi

• single membrane

plasmids

In prokaryotes, carry DNA not necessary for survival

• can be used by biochemists to insert genes of interest

Obligate Aerobe

Requires O2

Obligate Anaerobe

Dies in O2

Facultative Anaerobe

toggles between aerobic and anaerobic

Aerotolerant Anaerobe

Does not use O2 but tolerates it

Gram +

purple, thick peptidoglycan/lipoteichoic acid cell wall

Gram -

pink-red, thin peptidoglycan cell wall & outer membrane

Eukaryotes

• ETC in mitochondria

• large ribosomes

• reproduce via mitosis

Prokaryotes

• ETC in cell membrane

• small ribosomes

• reproduction via binary fission

• Plasmids carry DNA material, many have virulence factors

Episomes

plasmids that integrate into the genome

Prions

• infectious proteins

• trigger misfolding

• alpha helical —> beta pleated sheets

• lowers solubility

• causes mad cow disease

Viroid

plant pathogen

Microfilaments

Actin Filaments (smallest)

• Dynamic & flexible

• Role in:

  • Cell shape and movement

  • Muscle contraction (with myosin)

  • Cytokinesis (cleavage furrow)

  • Endocytosis & pseudopodia

• MCAT Buzzwords: Actin, myosin, lamellipodia, amoeboid movement

Microtubules

• Hollow tubes of tubulin dimers

• largest

• Form:

  • Mitotic spindle (metaphase, anaphase)

  • Cilia/flagella (9+2 structure)

  • Intracellular highways for transport via kinesin and dynein

  • Centrioles/centrosomes

• MCAT Buzzwords: Kinesin, dynein, colchicine, mitotic spindle, axoneme, 9+2

Intermediate Filaments

• Sturdy, rope-like, most stable of the three

• Structural reinforcement of the cell

• Different cell types have different IFs:

  • Keratin (epithelial cells)

  • Lamin (nuclear envelope)

  • Desmin (muscle)

• MCAT Buzzwords: Keratin, vimentin, lamin, desmosomes, nuclear lamina

Epithelia

thin tissue forming the outer layer of a body’s surface and lining the alimentary canal and other hollow structures

Parenchyma

functional parts of the organ

different types of epithelium

Simple —> one layer

Stratified —> multiple layers

Pseudostratified —> one layer but looks like multiple

Cuboidal —> cube shaped

Columnar —> long and narrow

Squamous —> flat, scale like

Connective Tissue

• Stroma (support, ECM)

• bone, cartilage, tendon, blood

Genetic Recombination

how bacteria get new DNA

Transformation

gets genetic info from environment

Conjugation

transfer of genetic info via conjugation bridge (bacteria “sex”)

F+ —> F- or Hfr —> recipient

• antibiotic properties can be transferred via this way

Transduction

transfer using bacteriophage

Transposons

genetic info that can insert/remove itself

• jumping genes that can move around

Capsid

protein coat around a virus

envelope

some viruses have lipid envelope

Virion

individual virus particle

Bacteriophage

bacteria virus; tall sheath injects DNA/RNA

Viral Genome

• may be DNA or RNA

• may be single or double stranded

if single stranded…

• positive sense: RNA can be translated into host cell

• negative sense: RNA replicase must synthesize a complimentary strand, which can then be translated

Retrovirus

• single stranded RNA

• reverse transcriptase needed to make DNA before becoming transcribed to RNA again and making proteins

Lytic Cycle

Virions made until cell lyses

Lysogenic Cycle

• virus integrates genome as provirus or prophage

• goes dormant until stress activates it —> goes to lytic cycle

Cell Cycle: G1

Make mRNA and proteins to prep for mitosis

Cell Cycle: G0

A cell will enter G0 if it does NOT need to divide

• enters after G1 if mitosis is not necessary

G1 checkpoint

Cell decides if it should divide; P53 is in charge

Cell Cycle: S

DNA is replicated

Cell Cycle: G2

Cell growth, makes organelles

G2 checkpoint

Check cell size & organelles

Cell Cycle: M

mitosis & cytokinesis

Positive Growth Signals

1. CDK + Cyclin create a complex

2. complex phosphorylates Rb to Rb+P

3. Rb changes shape, releases E2F

4. E2F releasing causes cell division to continue

Negative Growth Signals

1. CDK inhibitors block phosphorylation of Rb

2. So, E2F stays attached

3. Cell cycle halts

Sex Chromosomes

Sex determined by 23rd pair of chromosomes

• XX = female

• XY = male

X-linked disorders

males express, females can be carriers

Y chromosome

• little genetic information

• SRY gene = “sorry you’re a male”

Mitosis

• PMAT

• ploidy of 2n throughout

Prophase: DNA condenses, centrioles migrate to opposite poles & microtubules form, nuclear envelope disappears

Metaphase: “meet in the middle”, chromosomes meet in the middle

Anaphase: “apart”, sister chromatids separate and move to opposite poles

Telophase: chromosomes decondense, nuclear membrane forms, cytokinesis occurs (cytoplasm splits)

Meiosis

• PMAT 2x

Prophase I: chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs

Metaphase I: spindle fibers from opposing centrosomes connect to bivalents (at centromeres) and align them along the middle of the cell

Anaphase I: homologous pairs move to opposite poles of the cell, this is disjunction and it accounts for the Law of Segregation

Telophase I: chromosomes decondense, nuclear membrane MAY reform, cell divides (cytokinesis), forms two haploid daughter cells of unequal sizes

Prophase II: chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)

Metaphase II: spindle fibers from opposing centromeres attach to chromosomes (at centromere) and align them along the cell equator

Anaphase II: spindle fibers contract and separate the sister chromatids, chromatids (now called chromosomes) move to opposite poles

Telophase II: chromosomes decondense, nuclear membrane forms, cells divide (cytokinesis) to form four haploid daughter cells

crossing over

exchange of genetic material to form new chromosomes that are genetically unique

Nondisjunction

when sister chromatids/homologous pairs don’t separate properly during anaphase, results in aneuploidy

Law of Segregation

simply disjunction —> normal separation of chromosomes