the cell (b1- foundation)

Question 1

cell is defined as… + what do all cells contain

Answer 1

the basic structural and functional unit of of life

• can live as its own or in another organism

all cells contain:
- surrounded by a plasma membrane
- have cytosol, containing the organelles
- contain chromosomes/genetic material
- have ribosomes

Question 2

3 major differences between prokaryotic and eukaryotic cells

Answer 2

1. Size:
-prokaryotes: are smaller (typically 0.1-1.0 micron)
- eukaryotes: are much bigger (typically 10-100 microns in diameter)

2. Genetic Material:
- prokaryotes: genetic material is concentrated in the nucleoid
- eukaryotic cells: genetic material is in chromosomes in the nucleus

3. Cytoplasm:
- prokaryotes: all the material within the plasma membrane is cytoplasm
- eukaryotes: cytoplasm contained many membrane-bound organelles of specialized form and function

Question 3

what is cytology?

Answer 3

study of cells, focusing on their structure and function

• uses process called subcellular fractionation to separate the cell components
• then, biomarker enzymes are used to identify each of the separated organelles

Question 4

subcellular fractionation: first step and what the 3 processes used are

Answer 4

subcellular fractionation: process used to separate the cell components, involves 2 steps:

1. Tissue/cell homogenization: tissue is crushed by different methods and a homogenate is produce a homogenate

a. sonication: uses high-energy sound waves to rupture cell walls and membranes, releasing their contents. is effective for cell disruption and * highly suitable for protein extraction*.

b. chemical lysis: uses
- surfactants (dissolution of lipids)
- alkali (saponification- breaking down fats and oils into soap and alcohol- ex. NaOH)
- organic solvents: penetrate lipids and cause swelling of the cells (ex. toluene)

c. enzymatic lysis: enzymes are used to break down the cell. advantage is the specificity.
- enzymes used include: lysozyme, zymolase, cellulase, protease, glycanase (dont need to know all but maybe 1-2)

Question 5

what are microsomal fractions

Answer 5

fragments of the endoplasmic reticulum that are obtained through centrifugation

(ER too fat to come out by itself so it comes out in bits and pieces)

Question 6

subcellular fractionation: 2nd step and the steps used

Answer 6

2. centrifugation: used to separate the organelles based on different size, shape, and density. types of centrifugation:

a. differential centrifugation: means different times & speeds, so each step has a different time and speed (diff organelles come out at each)

order of organelles (1st to last): nuclei → mitochondria, chloroplasts, lysosomes, peroxisomes → plasma membrane, microsomal fragments, large ribosomes → small ribosomes → cytosol

b. density gradient centrifugation: all one big step and each of the organelle goes and settles at its density
- uses specific test tubes that have a pour at the bottom

Question 7

what are the biomarker enzymes for the following structures:

• nucleus
• mitochondria
• lysosomes
• Golgi apparatus
• microsomes
• cytoplasm

Answer 7

• nucleus → DNA (microsatellite markers), RNA
• mitochondria → inner membrane: ATP synthase
• lysosomes → cathepsin
• Golgi apparatus → galactosyl transferase
• microsomes → glucose-6-phosphate
• cytoplasm → lactate dehydrogenase

Question 8

structure of a nucleus

Answer 8

nuclear envelope: protective shell around the nucleus (made of 2 layers- inner and outer membrane), keeps DNA safe inside while separating it from the rest of the cell

nuclear pores (nucleoporins): tiny holes in the nuclear envelope, act like gates allowing important molecules (RNA and proteins) to move in and out of cell while keeping harmful substances out

nuclear lamina (jali like region): line inner part of the nuclear envelope, providing support and helps maintain shape of the nucleus

nucleolus: dense, round structure inside the nucleus, site where ribosomes are made

nucleoplasm: gel-like substance inside nucleus that surrounds the DNA and nucleolus (contains enzymes, proteins, and other molecules needed for the nucleus to function)

think nuclear EPL

Question 9

karyopherins

Answer 9

special proteins that act like “transport workers” for the nucleus

• help move important molecules (like proteins and RNA) in and out of the nucleus through the nuclear pores

2 types: importins (carry into the cell) and exportins (carry out of the nucleus)

Question 10

chromatin + 2 types + where is it located

Answer 10

chromatin are inside of the nucleus

functions of chromatin: primary protein components of chromatin are histones that compact the DNA and make nucleosomes, they prevent DNA damage, and control DNA replication and gene expression

2 types: euchromatin (loose & active - genes are on) & heterochromatin (tight & inactive- genes are off)

• euchromatin is less dense than heterochromatin and also looks lighter under a microscope

Question 11

nucleosome

Answer 11

section of DNA that is wrapped around a core of proteins

(histone + DNA)

when chromatin is extended and viewed under a microscope, structure resembles beads on a string

Question 12

biomedical importance of the nucleus

Answer 12

• controls hereditary characteristics of an organism & stores hereditary material in the form of DNA
• responsible for cell division, growth, and differentiation
• produces ribosomes (protein factories)
• site for transcription (mRNA are produced for protein synthesis*
• involved in DNA repair

Question 13

why are there RBC’s the only type of cells without mitochondria? viva question

Answer 13

because their main job is to transport oxygen, and mitochondria would actually compete for that oxygen

• since mitochondria need oxygen to produce ATP so would take some of the oxygen
• also more space for hemoglobin and easier to squeeze through areas without organelles
• instead, rely on glycolysis with does not require oxygen, allowing them to function effectively (since all they need energy for is to maintain their membrane)

Question 14

3 structures of a mitochondria

Answer 14

outer membrane: outermost layer of mitochondria, acts as protective barrier (allows free transportation of molecules), contains porins (special proteins that control what enters and exits)

inner mitochondrial membrane: site for electron transport chain (!!!), folded into structures called cristae (increase surface area for energy production)
- has protein complexes (I-V) that make up ETC to produce ATP (says you dont need to know names of each one yet)

matrix: inner fluid-filled space, contains enzymes, mitochondrial DNA, and ribosomes needed to make some of its proteins
- where the Krebs cycle (citric acid cycle) happens
- site for beta-oxidation of fatty acids
- ketone bodies production
- first 2 steps of the urea cycle
(memorize like 3-4 things from this list- matrix one)

Question 15

mitochondrial cytochrome P450 system

Answer 15

group of enzymes in different mitochondria cells that help modify molecules using oxygen, work different in different organs

steroid hormone production (placenta, adrenal cortex, ovaries, testes): hydroxylates cholesterol (adds an -OH group) to convert it into steroid hormones (like cortisol, aldosterone, estrogen, and testosterone)

bile acid synthesis (liver): helps convert cholesterol into bile acids, which are needed to digest and absorb fats

vitamin D formation (kidney): activates vitamin D by hydroxylating it, allowing body to use it for calcium absorption and bone health

Question 16

mitochondria DNA

Answer 16

is maternally inherited

• mutation rate is higher compared to nuclear DNA
• evolved from circular genome of bacteria that were engulfed by the early ancestor’s of today’s eukaryotic cell (she said this was wrong maybe though)

Question 17

how mtDNA (mitochondrial DNA) contributes to the ETC (electron transport chain)

Answer 17

mitochondrial DNA contains 13 genes that make proteins for the ETC

breakdown:
7 genes make protein for → complex I
1 gene → complex III
3 genes → complex IV
2 genes → complex v (ATP synthase)

means mitochondria partially control their own energy production by making key proteins needed for the ETC

Question 18

list some mitochondrial diseases

Answer 18

• fatal infantile mitochondrial myopathy and renal dysfunction (weak muscles, difficulty breathing, kidney problems)
• myoclonic epilepsy (seizures, nerve cells dont use energy right)
• ragged red fiber disease (muscle fibers appear “ragged” and red under microscope = muscle weakness)
• Alzheimer’s disease (nerve cell damage, memory loss and cognitive decline)
• diabetes mellitus (mitochondrial dysfunction in pancreatic cells, body has trouble using insulin)

Question 19

functions of the rough endoplasmic reticulum

Answer 19

• covered with ribosomes giving it that “rough” appearance
• key role in processing proteins to send to right destination which will either be a) secreted, b) inserted into cell membrane, or c) sent to organelles like lysosomes

protein modification: newly made proteins are folded and processed before being sent to final destination

3 types of protein modifications:
- chaperone proteins help in protein folding

trimming by proteases: some proteins need some parts cut off before fully functional
- proteases are enzymes that cut unnecessary sections

protein glycosylation: RER adds carbohydrate (sugar) chains to proteins to help them function properly, stay stable, and reach the right location

Question 20

glycation vs glycosylation

Answer 20

both are when sugars are attached to proteins BUT glycation can happen without enzymes whereas glycosylation needs proteins to happen

Question 21

5 functions of smooth endoplasmic reticulum (SER) + microsomal cytochrome P450 monooxygenase system

Answer 21

think lipids are smooth

• has different functions depending on the type of cell it is in

1. Lipid Production (in intestinal epithelium): makes phospholipids, glycolipids, and cholesterol

2. Glycogen Breakdown (in liver and muscle cells): helps break down glycogen (a stored form of sugar) into glucose when the body needs energy

3. Steroid Hormone Synthesis (in adrenal gland cells): produces steroid hormones, like cortisol and sex hormones (like estrogen and testosterone).

4. Calcium Storage and Release (in muscle cells): stores calcium ions and releases them when needed, which is crucial for muscle contraction.

5. Detoxification (in liver cells): helps neutralize toxins from the body, including drugs and harmful substances
- uses cytochrome p450 enzyme system (plays key role in breaking down chemicals)

Question 22

Golgi apparatus structure

Answer 22

• separated from nucleus by RER
• surface towards RER is called cis-golgi (“receiving” end of the Golgi apparatus- proteins from RER are sent here inside vesicles) screened and decided whether to keep or send back
• surface of last cistern of Golgi apparatus that is facing away from RER is called trans-golgi (is the “shipping” side of the Golgi apparatus- packs proteins into vesicles to send to target locations)

flow of proteins: RER → Vesicles → Cis-Golgi → Golgi Modification → Trans-Golgi → Final Destination

Question 23

main function + 2 types of modifications done by the Golgi apparatus

Answer 23

main function: modify, sort, & package proteins

• receives vesicles from RER w/ newly synthesized proteins, screened by cis-golgi (if not good then sent back to RER), rest of proteins are passed onto network

types of modifications:
1. Glycosylation: attaches carbs (sugars) to proteins or lipids to help with cell recognition, signaling, and stability
- 2 types: N-Glycosylation (sugars added to -NH2 group (amide), mostly in membrane proteins and secreted proteins like antibodies) and O-Glycosylation (sugars are added to -OH (hydroxyl) group, mainly in mucus proteins)

2. Phosphorylation: adds phosphate groups to activate, deactivate, or direct them to right location

Question 24

3 destinations of proteins after being packaged by the Golgi apparatus

Answer 24

• lysosomes
• secreted out of cell
• become part of the cell (cell membrane)

Question 25

function of the lysosomes

Answer 25

- numerous in phagocytes and in cells with more metabolic activity - responsible for digestion of both **intra** and **extracellular** substances have group of enzymes called **hydrolases**: digest excess or worn out organelles, food particles, and engulfed viruses or bacteria

Question 26

how are lysosomal enzymes (that function inside the lysosomes) made?

Answer 26

enzymes (proteins) made for lysosomes are first made in the **RER** where sugar attaches are attached to them through **N-linked glycosylation** → sent to Golgi apparatus where more chemical modifications happen and special tag of **mannose-6-phosphate (M6P)** are added to these enzymes → packed into vesicles and sent to **endosomes** (sorting compartments) → endoscopes fuse with lysosomes, delivering the enzymes **M6P is important b/c otherwise not be sent to the lysosomes**

Question 27

lysosomal storage diseases

Answer 27

1. **I-cell disease**: this is when the M6P protein is missing and ends up secreted outside of the cell instead of going to the lysosome 2. **sphingolipidosis**: defective enzymes fail to break down sphingolipids (type of fat) - exs. *Gaucher's disease, niemann-pick disease* 3. **gangliosidosis**: failure to break down gangliosides (type of lipid in nerve cells) - ext. *tay-sachs disease, leukodystrophies* - I only wrote down these examples, there are more on the slides

Question 28

4 types of hydrolases in lysosomes (2 examples of each)

Answer 28

**polysaccharide hydrolyzing enzymes**: digest polysaccharides into simpler sugars - ex. *beta-galactosidase, alpha-glucosidase, lysozyme* **lipid hydrolyzing enzymes**: digest lipids (fats & phospholipids) - ex. *fatty acyl esterase, phospholipases* **protein hydrolyzing enzymes**: digest proteins into smaller peptides or amino acids - ex. *cathepsins, collagenase, elastase, peptidases* **nucleic acid hydrolyzing enzymes**: digest genetic material (DNA & RNA) - ex. *ribonuclease, deoxyribonuclease*

Question 29

3 things that lysosomes can do (biomedical importance)

Answer 29

**exocytosis**: release of enzymes outside of the cell - process is useful for destroying bacteria, damaged tissues, or extracellular debris **autophagy**: 'self eating' - lysosomes digest worn out or damaged cell parts - damaged material is enclosed in vacuole and fused with lysosome for digestion **heterophagy**: "foreign-eating" - lysosomes digest materials from outside the cell - happens when cell engulfs foreign particles (phagocytosis or endocytosis), forming vacuole that fuses with a lysosome)

Question 30

peroxisomes (general overview + enzymes)

Answer 30

**peroxisomes**: small organelles found in most cells, especially prominent in **leukocytes** (white blood cells) and **platelets** - involved in detoxification, lipid metabolism, and biosynthesis **enzymes**: catalase & peroxidase → help neutralize harmful free radicals by breaking down *hydrogen peroxide (H₂O₂) into water (H₂O) and oxygen (O₂)*. - prevents oxidative damage to the cell *remember them from hydrogen peroxide*

Question 31

5 functions of peroxisomes

Answer 31

**lipid metabolism**: breakdown of long-chain fatty acids (type of fats) into smaller pieces that can be used for energy (*fatty acyl coA synthetase*) **synthesis of glycerophospholipids**: peroxisomes can make this certain fat that is needed to form cell membranes **formation of plasmalogens**: type of fat that is especially important for the nervous system, important content of myelin in nerve cells **synthesis of bile acids**: bile acids are needed for digesting fats and absorbing important vitamins like *vitamin A and vitamin K* **oxidation of D-amino acids and uric acids** in animal cells: help break down D-amino acids (type of protein building block) and uric acid (waste product) to keep body in balance

Question 32

main peroxisomal disorder

Answer 32

**zellweger syndrome (cerebrohepatorenal syndrome)**: most severe peroxisomal disease caused by **absence of functional peroxisomes** → accumulation of long chain fatty acids mostly in the brain **effects**: - decreased formation of plasmalogens → affects nerve cell function - defective bile acid synthesis → poor fat absorption & vitamin deficiency

Question 33

prokaryotic ribosomes vs eukaryotic ribosomes

Answer 33

**prokaryotic ribosomes**: have 70S ribosomes - consists of: small subunit = 30S, large subunit= 50S **eukaryotic ribosomes**: have 80S ribosomes - consists of: small subunit = 40S, large subunit = 60S

Question 34

ribosome structure

Answer 34

- site of **protein synthesis** in the cell - made from complexes of rRNAs and proteins - about 37-62% rRNA and the rest is proteins - 2 subunits: large & small

Question 35

cytoplasm vs cytoskeleton

Answer 35

- not the same thing, and shouldn't be used interchangeably **cytoplasm**: gel-like substance inside cell membrane, made up of **cytosol** (the fluid part) & various organelles, excluding the nucleus - basically everything inside the cell except for the nucleus **cytoskeleton**: network of protein filaments and tubules that are within the cytoplasm - provides structure, support, and shape to the cell and plays major role in cell movement, division, and transport of materials within cell

Question 36

biomedical importance of the cytoplasm

Answer 36

- gives cell its shape (fills out the cell and keeps organelles in their place) - contains **enzymes** that: aid in metabolic activity and break down waste - **cytoplasmic streaming**: movement of the cellular materials around the cell

Question 37

3 main types of filaments in the cytoskeleton (explain them just briefly) **UQ**

Answer 37

**cytoskeleton**: give cell shape & association w/ extracellular connective tissue **1. Microfilaments**: made of actin proteins and are the thinnest filaments in the cytoskeleton, *help in muscle contraction, cell division, and immune responses* **2. Intermediate filaments**: stronger & more stable than microfilaments and made of different proteins, like keratin (more on other flashcard), *provide structural support by anchoring cells and connecting them to their environment* **3. Microtubules**: made up of tubulin proteins (alpha and beta tubulins) & are the thickest filaments in the cytoskeleton, *enable transport within the cell + critical role in cell division*

Question 38

microfilaments (cytoskeleton) + what their roles are

Answer 38

- made up of **actin proteins** and are the **thinnest** filaments in the cytoskeleton play an important role in: - **muscle contraction**: actin filaments interact w/ myosin to help muscles contract and relax - **cytokinesis during mitosis**: help cell divide by forming a ring that pinches the cell into two - **diapedesis of white blood cells**: actin filaments help white blood cells (WBCs) squeeze through blood vessel walls to reach infection sites **phagocytosis by WBCs**: WBCs use actin to engulf and digest harmful particles like bacteria.

Question 39

intermediate filaments (cytoskeleton) + their roles

Answer 39

these filaments are stronger and more stable than microfilaments and are made of different proteins, such as: **Keratin** (found in skin cells), **Vimentin** (in connective tissue), **Nestin** (in nerve cells), **Lamin** (in the nucleus). **main functions**: - anchor cell to extracellular matrix: helps cell stay in place within tissues. - connect the cell to other cells: Intermediate filaments help cells stay attached to each other, which is important for tissue stability

Question 40

microtubules (cytoskeleton) + their roles

Answer 40

made of **tubulin proteins (alpha and beta tubulins)** and are the thickest filaments in the cytoskeleton **functions**: - **intracellular transport**: act as tracks for transporting organelles and vesicles within the cell, using motor proteins like dyneins and kinesins. - **cell division**: during mitosis, microtubules help form the mitotic spindle, which connects to the kinetochore on chromosomes and ensures that they are properly separated into two new cells

Question 41

fluid mosaic model

Answer 41

used to describe the cell's membrane structure **fluid**: lipids & proteins can move sideways, like a fluid, making it flexible and dynamic **mosaic**: membrane has a pattern (mosaic) of proteins, lipids, and carbohydrates that are scattered unevenly, like tiles in a mosaic other info from slides: phospholipids arranged in bilayers, driven by hydrophobic effects. lateral movement is allowed but flip flop movement is restricted (flippases transfer PL from inner to outer layer)

Question 42

the 3 parts of a cell membrane (structure)

Answer 42

**lipids**: phospholipids, glycosphingolipids, & cholesterol **proteins**: integral & peripheral **carbohydrates**: glycolipids & glycoproteins

Question 43

cell membrane structure: lipids (3 types)

Answer 43

all major lipids are **amphipathic** (have both hydrophilic and hydrophobic parts) **1. phospholipids**: main lipids in the cell membrane - form the bilayer, heads face outward while tails face inward - (structure on a different card) **2. glycosphingolipids**: sugar-containing lipids that contain **ceramide** backbone - include *galactosyl ceramide* and *glucosyl ceramide* - found mainly in plasma membrane: help w cell recognition & communication **3. cholestrol**: crucial role in maintaining membrane fluidity (prevents membrane from becoming too rigid or too fluid) - has an **OH group at carbon 3** = hydrophilic property

Question 44

structure of a phospholipid

Answer 44

**polar phosphate head** (hydrophilic part) attached to **2 nonpolar fatty acid chains** (hydrophobic part) **C1 (fatty acid chain)**: usually contains saturated fatty acids (no double bonds) = straight anymore rigid **C2 (fatty acid chain)**: usually contains unsaturated fatty acids (w/ double bonds) = **kink** that increases membrane fluidity external layer: contains **choline-containing phospholipids** *MCQ* inner layer: contains **ethanolamine** and **serine-containing phospholipids** *I think this means how one tail goes down straight and the other tail has a kink in it*

Question 45

cell membrane structure: proteins

Answer 45

**peripheral proteins**: loosely bound to surface of membrane (either inner or outer side) - roles in: support of cell membrane, cell communication (i.e. receptors), enzymatic functions **integral proteins**: span the membrane, either partially or completely - 2 classes: transmembrane & transport **transmembrane proteins**: go all the way across the membrane - typically have **alpha helices** that help them transverse the lipid bilayer **transport proteins**: ion channels, protons pumps, G-protein couples receptors (GPCRs- signal transduction and communication)

Question 46

cell membrane structure: carbohydrates (**glycocalyx**)

Answer 46

glycocalyx means **glycolipids & glycoproteins** together, play role in: - **holding onto water**, preventing dehydration (glycolipids) - **cell-cell recognition**: help cells identify each other, important for immune function - communication b/w cells - **Antigenicity**: They allow the immune system to recognize self cells from foreign cells. - **intercellular adhesions**: help cells stick together in tissues

Question 47

specialized features of the membrane: lipid rafts, caveolae, tight junctions

Answer 47

**Lipid Rafts**: subdomains of plasma membrane, rich in cholesterol and glycosphingolipids - functions: endocytosis, signal transduction, & binding of pathogens **Caveolae**: derived from lipid rafts, small, flask-shaped invaginations of the membrane that help with endocytosis (the process of taking in substances). - contain protein *caveolin* **Tight Junctions**: tightly seal spaces b/w cells, preventing molecules from passing through the space b/w cells. - contain *claudin* and other proteins

Question 48

functions of the cell membrane

Answer 48

- defines **boundaries** and forms closed compartments around cellular protoplasm (forming organelles) - **selective permeability**: small molecules like O2 & CO2 can pass easily, large molecules or charged ions need transport proteins to get across **localizes enzymes**: enzymes embedded in the membrane help carry out chemical reactions in a specific location = increased efficiency **cell identity marker**: glycolipids & glycoproteins act as "ID tags" = help immune system recognize self and foreign) - attachment for **cytoskeleton** - **excitation-response coupling**: receptors on membrane detect signals (hormones, neurotransmitters, & electrical signals), signals trigger response inside cell - **facilitates cell adhesion & interactions**: cell stick to each other using special proteins on their membranes = tissue formation *normal membranes = normal cell function*

Question 49

3 forms of transport across the membrane

Answer 49

1. simple diffusion, 2. facilitated diffusion (both passive transport) 3. active transport

Question 50

Simple diffusion (1st type of passive transport)

Answer 50

materials move down their concentration gradient through the phospholipid bilayer - move from **high to low concentration** *ex. oxygen diffusing in or CO2 diffusing out* (know this example)

Question 51

facilitated diffusion (2nd type of passive transport) + types of transport proteins/channels

Answer 51

passive movement of substance into or out of cell by means of **carrier proteins or channel proteins** moves from **high to low conc.** transport proteins: **Transporters** (Carrier proteins): for glucose **Aquaporins**: for water ion channels: **ligand-gated channels**: open when a specific molecule (ligand) binds to them - ex. neurotransmitters open channels in nerve cells (*acetylcholine receptor*) **voltage-gated channels**: open or close based on changes in electrical change (voltage) across the membrane - ex. nerve signals use voltage-gated Na+ and K+ channels to send impulses (*depolarization*) *know the examples*

Question 52

how many distinct aquaporins have been identified? what does a defect in aquaporin-2 lead to?

Answer 52

5 distinct aquaporins (AP-1 to AP-5) defect in aquaporin-2 = **diabetes insipidus**

Question 53

2 types of active transport: primary & secondary

Answer 53

**primary**: directly uses energy from breakdown of ATP to move molecules - exs. *Na+/K+ ATPase, H+/K+ ATPase, Ca2+ ATPase, ABC ("ATP-Binding Cassette") **secondary**: does not use ATP directly, primary transport causes a new conc. gradient - exs.: **symport pumps (co-transport)**: both molecules move in the same direction - *glucose/Na+ symporter*: Na+ flow into cell also brings glucose along with it - *Na+/Amino acids* **antiport pumps (exchanger)**: molecules move in opposite directions - exs. *Na+/Ca2+*: Na+ enters cell while Ca2+ exits

Question 54

2 processes for movement of large molecules in/out of cell

Answer 54

exocytosis & endocytosis (3 further classifications of endocytosis)

Question 55

3 types of endocytosis

Answer 55

**endocytosis**: cell membrane folds in, forming vesicle to bring substances inside - used for large molecules, nutrients, and even whole bacteria 3 types: **1. Phagocytosis** ("Cell Eating"): cell engulfs large particles (like bacteria or debris), fuse w/ lysosome for digestion - *ex. white blood cells use phagocytosis to destroy bacteria* **2. Pinocytosis** ("Cell Drinking"): cell takes in liquids and dissolved molecules by forming small vesicles, non-specific process - *ex. cells absorb nutrients from the fluid around them* **3. Receptor-mediated Endocytosis**: cell uses specific receptors to grab and pull in certain molecules, triggered by molecular signals - *ex. cells take in cholesterol (LDL) using receptors*

Question 56

exocytosis

Answer 56

reverse of endocytosis vesicle from inside cell moves to the cell membrane, **fuses** with it, and the contents are **secreted** *examples*: - neurons release neurotransmitters to send signals - glands release hormones into the blood - cells remove waste after digestion