Exam 2

Question 1

Define cytology.

Answer 1

The study of cells

Question 2

Distinguish among extracellular fluid, interstitial fluid and intracellular fluid.

Answer 2

Extracellular fluid (ECF) is outside of the cells. Interstitial fluid is between the cells, in tissue spaces and intracellular fluid (ICF) is inside the cells.

Question 3

Describe the composition/charge difference of the ICF compared to the extracellular environment (ECF).

Answer 3

Intercellular fluid has high potassium (k+) inside. Inside is (-) compared to the outside in extracellular fluid, which is (+). It has many (-) charged proteins, fewer positive molecules/ions. Has Cytoskeleton, carbs, lipid storage, inclusions and organelles. Extra

Question 4

Be able to describe the importance of cell division.

Answer 4

Cells divide to help with growth, development, and tissue repair. Its like a while process called the cell cycle, where the cell gets ready for division and then actually divides into two identical cells. During division, the nucleus divides in a process called mitosis, and then the rest of the cell splits in cytokinesis.

Question 5

Be able to list the phases of the cell cycle in the proper order.

Answer 5

Interphase: G1 phase, S phase, G2 phase

M (mitotic) phase: mitosis (prophase, metaphase, anaphase telophase, cytokinesis.

Question 6

Distinguish between interphase and M-phase. List the subdivisions in each (in order).

Answer 6

G1 phase, where the cell grows and carries out its Normal function
S phase, where DNA replication occurs and the cell makes a copy of its genetic material.
G2 phase, where the cell continues to grow and prepares for division.

M-phase, also known as the mitotic phase, is the actual division phase. It consists of two subdivisions:
Mitosis, wich includes prophase, metaphase, anaphase and telophase. During mitosis, the nucleus divides.n
Cytokinesis, where the rest of the cell, such as the cytoplasm and organelles, divides to form two separate cells.

Question 7

Define mitosis and cytokinesis.

Answer 7

Mitosis: nucleus divides, each daughter cell gets 1 complete set of DNA. Cytokinesis: Cytoplasm with organelles divides.

Question 8

Describe the events that take place during G1, S and G2 phase.

Answer 8

SO, in a nutshell, G1 is about growth and normal functions, S is about DNA replication, and G2 is about final preparations. It’s all part of the cells journey towards division. Generally, it can range from a few hours to several days.

Question 9

Describe the process of DNA replication/duplication that occurs in S phase.

Answer 9

During the S phase, DNA replication occurs. Its like the cell making a copy of its genetic material. Imagine it as the cell creating a duplicate of its instruction manual, so it has an extra set of all the important information. This replication process ensure that each new cell formed during division will have a complete set of DNA. Its like having a backup plan for the cells genetic code!

Question 10

Be able to describe what semi-conservative replication is.

Answer 10

So, semi-conservative replication is a fancy term for the way DNA replicates itself. Its like a clever recycling system! During replication, the DNA molecule splits into two strands, and each strand serves as a template for the creation of a new complementary strand. So, in the end, you have two new DNA molecules, each with one original strand and one newly synthesized strand. Its like keeping half of the old DNA and adding half of the new DNA to create a perfect blend.

Question 11

Prophase:

Answer 11

this is like the preparation phase. The chromosomes condense and become visible. The nuclear envelope starts to break down, and the spindle fibres begin to form.

Question 12

Metaphase:

Answer 12

this is where the action happens. The chromosomes line up in the middle of the cell, forming whats called the metaphase plate. The spindle fibres attach to the centromeres of each chromosome. Its like a neat lineup of chromosomes, ready to be divided.

Question 13

Anaphase:

Answer 13

time for separation. The sister chromatids of each chromosome separate and are pulling towards opposite ends of the cell by the spindle fibres. Its like the chromosomes getting pulled apart.

Question 14

Telophase:

Answer 14

things start to wind down. The chromosomes reach the opposite ends of the cell and a new nuclear envelope starts forming around each set of chromosomes. Its like the chromosomes finding their new homes and getting cozy

Question 15

Cytokinesis:

Answer 15

the final act. The cell membrane pinches in, dividing the cytoplasm into two separate cells. Each cell has its own nucleus and complete set of chromosomes. Its like there cell splitting into two, ready to start a new chapter.

Question 16

Describe the cleavage furrow.

Answer 16

The cleavage furrow is like a little groove that forms during cytokinesis. Its like a tiny indentation that appears in the cell membrane as the cell divides. Picture it as a little pinch or a crease that gradually deepens until the cell separates into two.

Question 17

DNA

Answer 17

its like the master blueprint of life. DNA carries all the genetic information in our cells. Its made up of a long sequence of nucleotides, which are like the building blocks of DNA

Question 18

Genes

Answer 18

Think of genes as specific sections of DNA. They contain instruction for making proteins, which are essential for various functions in our bodies. Genes determine our traits and characteristics, like eye colour or height. Each gene has a specific location on a chromosome.

Question 19

mRNA

Answer 19

mRNA or messenger RNA, is like a courier that carries the genetic instructions from the DNA too the protein-making factories in our cells called ribosomes. Its like a copy of the genes instructions that can easily transported.

Question 20

Amino acids

Answer 20

these are the building blocks of proteins. There are 20 different types of amino acids, and they links together in a specific sequence dictated by the mRNA. Its like putting a unique sequence of lego blocks to create different proteins.

Question 21

Proteins

Answer 21

proteins are like the workhorses of our cell. They perform various functions, like enzymes that speed up chemical reactions or structural proteins that give cells their shape. The sequence of amino acids determines the structure and function of the protein.

Question 22

Be able to discuss how the following are related to one another: DNA, genes, mRNA, amino acids, protein.

Answer 22

n a nutshell, DNA contains genes, genes are transcribed into mRNA, mRNA guide the assembly of amino acids, and amino acids come together to form proteins. Its like a fascinating chain of events that ultimately leads to creation of proteins, which are vital for life.

Question 23

Transcription

Answer 23

is the process where genetic information from DNA is copied in mRNA. It occurs in the nucleus of eukaryotic cells.

Question 24

Translation

Answer 24

is the process where mRNA is used as a template to build a protein. It takes place in the ribosomes, which can be found in the cytoplasm of both eukaryotic and prokaryotic cells.

Question 25

Describe the difference between the states of the DNA of genes that are active (expressed) vs. inactive (not expressed).

Answer 25

Although all cells have the same DNA with the same genes, not all genes are expressed or turned into proteins. The state of DNA is active genes, is open and accessible, allowing transcription factors and RNA polymerase to bind and initiate transcription. In inactive genes, the DNA is tightly packed and inaccessible, preventing gene expression. So, the difference lies in the accessibility of the DNA

Question 26

Explain how transcription of the template strand is initiated, how the mRNA is elongated, (ie. complementary base pairing) and how transcription is terminated.

Answer 26

So, transcription starts with the promoter, builds the mRNA using complementary base pairing and ends at the terminator. Its like writing out a sentence, with the DNA providing a script.

Question 27

The cell

Answer 27

Cell theory: based on Robert Hooke’s research - Cells are the building blocks of all plants and animals. – All cells come from the division of preexisting cells – Cells are the smallest units that perform all vital physiological functions – Each cell maintains homeostasis at the cellular level

Question 28

Cytoplasm

Answer 28

intracellular fluid (cytosol) + organelles

Question 29

Nucleus:

Answer 29

controls cellular activities

Question 30

Plasma membrane

Answer 30

barrier

Question 31

Cellular environment

Answer 31

Fluid in compartments: movement between compartments

Question 32

Extracellular fluid (ECF)

Answer 32

outside of cells – Interstitial fluid (between cells, in tissue spaces) – Blood plasma, lymph, cerebrospinal fluid

Question 33

Intracellular fluid (ICF)

Answer 33

inside of cells – Cytosol with nutrients, ions, proteins, wastes

Question 34

ICF vs. ECF

Answer 34

• Intracelluar fluid (inside cell) – High potassium (K+) inside – Inside (-) compared to outside (+) • Many (-) charged proteins • Fewer positive molecules/ions – Cytoskeleton – Carbs, lipid storage, inclusions – Organelles • Extracellular fluid (outside cell) – High sodium outside (Na+) – Extracellular matrix

Question 35

The nucleus

Answer 35

• Largest organelle (10% total cell volume) with nuclear membrane, nucleoplasm, nucleolus, pores • Genetic library of DNA (chromatin, chromosomes): genes containing genetic code – Directs synthesis of RNA, proteins • Control center: cell structure /function – What, where, when, how much protein made

Question 36

G1

Answer 36

• G = gap We will assume preparing to divide: • Lasts about 8-10hr • Environmental monitoring • Cell grows • Makes new organelles and other structures for replication – Starts to copy centrosome so have 2 pairs centrioles later – Need them for mitotic spindle production

Question 37

S- phase

Answer 37

• DNA synthesis/duplication (~8hr) • Goal: make another copy of all DNA molecules – need 2 complete sets for 2 identical daughter cells • Many enzymes involved • Unwind DNA to separate the DNA strands and copy

Question 38

DNA replication in S phase

Answer 38

• Two identical DNA molecules formed from original DNA • Semi-conservative replication: 1 old and 1 new strand/ final DNA molecule • New DNA rewinds around histone proteins • Important that new DNA is not damaged or broken!

Question 39

Semi-conservative replication

Answer 39

1 old and 1 new strand/ final DNA molecule

Question 40

G2

Answer 40

• After S phase, before mitosis (~4-6hr) • Monitoring environment • Cell growth continues • Final preparation • Centrosome replication complete: 2 pairs of centrioles for mitotic spindle production!

Question 41

Mitosis

Answer 41

nucleus divides, each daughter cell gets 1 complete set of DNA! – Continual process!...0.5 -1.5 hrs – Stages: PMAT – Vocab: Chromatin, chromosome, chromatids

Question 42

Cytokinesis

Answer 42

Cytoplasm with organelles divides – Begins in late anaphase+

Question 43

DNA

Answer 43

genetic instructions

Question 44

Gene

Answer 44

segments of DNA code for RNA→ protein

Question 45

Overview: From DNA to protein

Answer 45

• DNA directs its own replication -we saw that during interphase! • DNA directs protein synthesis (we will see this now!), but too big to leave nucleus • So- mRNA made, carries protein coding message to cytoplasm • Protein made in cytoplasm • DNA: genetic instructions – Gene: segments of DNA code for RNA→ protein • DNA → mRNA (transcription) – Nucleus • mRNA → protein (translation) – Cytoplasm, ribosomes

Question 46

Inactive genes

Answer 46

DNA supercoiled not easily accessed

Question 47

Active “expressed” genes

Answer 47

DNA uncoiled, exposed for transcription of mRNA

Question 48

Transcription (DNA→ mRNA)

Answer 48

• Remember nucleotides? Read as 3 nucleotides (base triplet) • 1 DNA triplet → 1 mRNA codon → 1 amino acid • DNA: 2 strands, in transcription- • Template DNA strand – Transcribed strand, contains gene’s promoter “start sequence” • Coding DNA strand – Not transcribed, has same code as mRNA built except U not T

Question 49

Template DNA strand

Answer 49

Transcribed strand, contains gene’s promoter “start sequence”

Question 50

Coding DNA strand

Answer 50

Not transcribed, has same code as mRNA built except U not T

Question 51

Initiation

Answer 51

– DNA is unwound – RNA polymerase binds DNA promoter on template strand (contains gene) – RNA polymerase begins to make new RNA polymer

Question 52

Elongation

Answer 52

– RNA polymerase moves along DNA template and assembles mRNA – Complementary base-pairing: H bonds between template DNA and new mRNA (U not T!!) – Covalent bonds between mRNA ribonucleotides – 1 DNA base triplet transcribed into 1 codon (mRNA -3 ribonucleotide sequence)

Question 53

Termination:

Answer 53

At end of gene: stop/termination signal • special nucleotide sequence - RNA polymerase released - pre-mRNA transcript released

Question 54

RNA processing of pre-mRNA

Answer 54

• Result of transcription: pre - mRNA transcript produced (AKA primary transcript) – Many codons long – But –immature and can’t leave nucleus yet! • Pre-mRNA transcript – Contains: • Exons: coding regions, codes for proteins: KEEP • Introns: non-coding regions, does not code for proteins: REMOVE

Question 55

Exons

Answer 55

coding regions, codes for proteins: KEEP

Question 56

Introns

Answer 56

non-coding regions, does not code for proteins: REMOVE

Question 57

RNA processing before exits nucleus

Answer 57

• Splicing: cut out mRNA introns, connect exons – Note: it isn’t always this easy ☺ • Capping • Poly A tail

Question 58

Splicing

Answer 58

cut out mRNA introns, connect exons – Note: it isn’t always this easy ☺

Question 59

Protein synthesis: translation mRNA→protein

Answer 59

• Translation: – 1 codon on mRNA translated into 1 amino acid in protein – Purpose: make a specific polypeptide protein – Location: ribosomes • Free: in cytosol • Bound: to organelle membrane (ie. RER)

Question 60

Reading the genetic code

Answer 60

• We started with a base triplet (3 nucleotides -DNA) • We made a complementary codon (3 ribonucleotides - mRNA) • 1 codon translates into 1 amino acid – Each amino acid can be specified by >1 codon • Polypeptides (proteins) made from combination of 20 amino acids

Question 61

mRNA→protein: who are the players?

Answer 61

• mRNA transcript with codons • tRNAs: picks up amino acids from cytoplasm, “transfers” to ribosome – Anti-codon of tRNA: binds complementary mRNA codon – Amino acid attached at other end of tRNA, transferred to growing peptide • Ribosome: “reading machines” – Made of rRNA

Question 62

Translation: Initiation

Answer 62

• Ribosome binds mRNA sequence near mRNA cap • Finds start codon: AUG • Initiator tRNA (with anti-codon UAC and special aa “MET”) binds to start codon

Question 63

Translation: Elongation

Answer 63

• Additional amino acids added – Another tRNA (with anti-codon and attached aa) pairs with next codon – Ribosome links the amino acids of the tRNA by peptide bond – mRNA moved through ribosome – After tRNA transfers aa, empty tRNA falls off and is “recharged”

Question 64

Translation: Termination

Answer 64

• Elongation continues until “Stop” codon (UAA, UAG, UGA) signals termination • Polypeptide protein released • Protein can’t function yet, must fold correctly first! • Polyribosomes: – Multiple ribosomes translate same mRNA in succession – More protein made in shorter time!

Question 65

When things go awry…

Answer 65

• Mutations: permanent changes in a cell’s DNA • Nucleotide sequence change→ mRNA change → can change amino acid sequence → can change protein’s function • With DNA mutation can affect protein structure – Structure dictates function! – Without normal structure, protein can’t function normal

Question 66

Cell (plasma) membrane functions

Answer 66

• Physical barrier: intracellular and extracellular, covers, protects cell • Gatekeeper: regulates exchange with environment: ions, nutrients, waste • Environmental sensor: monitors environment, ECF composition, chemical signals, cell communication • Structural support: anchors cells to other cell, ECM

Question 67

Plasma membrane composition

Answer 67

• Lipids – Phospholipids – 2 layers! – Cholesterol – Glycolipids • Proteins – Proteins – Glycoproteins • Membrane is asymmetrical

Question 68

Plasma membrane fluidity

Answer 68

• Fluid mosaic model: membrane structure – Sea of phospholipids, protein “icebergs” and islands: mosaic – Phospholipid and proteins interact, move side to side: fluid • Circular membrane held together by weak hydrophobic interactions – Hydrophobic non-polar fatty acid tails of phospholipids • Fluidity influenced by various factors

Question 69

Plasma Membrane Lipids

Answer 69

• Phospholipid bilayer (2 layers!) – Polar hydrophilic head – Non-polar hydrophobic tails – Barrier to most polar/charged/large molecules • Cholesterol – Strengthens membrane – Maintains membrane stability with temp changes

Question 70

Plasma membrane “accessories”

Answer 70

Accessories with carbohydrates • Glycolipids: lipid with carb • Glycoproteins: protein with carb • Glycocalyx: Carb portion is ”coating of sugar” on cell surface – Lubrication/protection – Anchoring/locomotion – Recognition (self): signature ID tags

Question 71

Glycolipids

Answer 71

lipid with carb

Question 72

Glycoproteins

Answer 72

protein with carb

Question 73

Glycocalyx

Answer 73

Carb portion is ”coating of sugar” on cell surface – Lubrication/protection – Anchoring/locomotion – Recognition (self): signature ID tags

Question 74

Plasma membrane protein types

Answer 74

1. Peripheral: loosely bound on one side of membrane 2. Integral: usually span entire membrane width (transmembrane proteins) – Hydrophilic and hydrophobic parts – Some are glycoproteins

Question 75

Peripheral proteins

Answer 75

loosely bound on one side of membrane

Question 76

Integral proteins

Answer 76

usually span entire membrane width (transmembrane proteins) – Hydrophilic and hydrophobic parts – Some are glycoproteins

Question 77

Functions of membrane proteins

Answer 77

• Similar lipids in cell membranes • Different membrane proteins- give cells unique functions • Some functions of membrane proteins: – Transport – Attachment – Receptors

Question 78

Transport: integral proteins

Answer 78

– Ion channel: specific ions • Hydrophilic part lines channel – Carrier: specific solutes bind (glucose) • Some do not require energy • Some do: ATP powered pumps-require ATP

Question 79

Attachment (integral or peripheral)

Answer 79

– Maintain cell shape, position; membrane protein position – Inside bound to cytoskeleton – Outside bound to: • ECM • Other cells: cellular junctions

Question 80

Receptors: integral proteins

Answer 80

– Bind ligands (chemicals) • Hormones (Insulin to insulin receptor) • Neurotransmitter to muscle cell • Triggers cell change – Some receptors linked to channel proteins • “Ligand gated” channel- channel opens/closes • Changes membrane permeability

Question 81

Plasma membrane

Answer 81

barrier between cell cytosol (inside) and interstitial fluid (outside ECF

Question 82

Intracellular

Answer 82

more K+, enzymes/proteins, glycogen, has organelles

Question 83

Extracellular

Answer 83

more Na +, Ca 2+, and Cl-

Question 84

Plasma membrane permeability

Answer 84

• Permeability: how easily substances move through a membrane • Plasma membrane is selectively permeable: some substances cross more easily than others – Maintain differences across membrane – Result of lipid and protein distribution in membrane – Maintains internal order despite changes outside cell- “homeostasis”!

Question 85

Permeability

Answer 85

how easily substances move through a membrane

Question 86

Plasma membrane is selectively permeable

Answer 86

some substances cross more easily than others

Question 87

Transport processes

Answer 87

• Passive transport: NO energy used, move across from higher to lower concentration – Simple diffusion: solutes directly cross membrane – Osmosis: water through membrane or channel – Facilitated diffusion: solutes through specific channel or a carrier molecule, (but no energy is used!!) • Active transport: energy used (ie. ATP) to get across – Primary active transport: • Move substances from lower to higher concentration – Vesicular transport • Membrane bound sacs (vesicles)

Question 88

Passive transport

Answer 88

NO energy used, move across from higher to lower concentration

Question 89

Simple diffusion

Answer 89

solutes directly cross membrane

Question 90

Osmosis

Answer 90

water through membrane or channel

Question 91

Facilitated diffusion

Answer 91

solutes through specific channel or a carrier molecule, (but no energy is used!!)

Question 92

Active transport

Answer 92

energy used (ie. ATP) to get across

Question 93

Primary active transport

Answer 93

Move substances from lower to higher concentration

Question 94

Vesicular transport

Answer 94

Membrane bound sacs (vesicles)

Question 95

Diffusion

Answer 95

solute moves from area of higher solute concentration to lower concentration (down its concentration gradient) • Driving force: high speed motion of atoms and collisions – Collisions occur more in crowded (concentrated) area • No energy needed: Diffusion is ALWAYS passive • But! remember cell has selectively permeable plasma membrane = barrier

Question 96

Simple diffusion

Answer 96

move freely through plasma membrane down concentration gradient – Remember hydrophobic core = barrier – Small, nonpolar, lipid soluble substances move through easily • Diffusion rate increases with: – Shorter diffusion distance – Increased lipid solubility • Lipids, steroids, FA cross – Smaller size – Steeper concentration gradient – Higher temperature – Increased surface area • Physiological relevance?

Question 97

Facilitated diffusion

Answer 97

Channel or carrier integral membrane proteins help (facilitate) small polar, charged or large molecules – PASSIVE: no energy needed – Must travel down their concentration gradient – Specific: interaction with protein transporter – Channels for ions (leak or gated), H20 – Carriers: can become saturated • All seats filled!

Question 98

Osmosis

Answer 98

movement of water (solvent) across semi-permeable membrane

Question 99

Osmolarity

Answer 99

total solute concentration in solution

Question 100

Osmosis

Answer 100

• Osmosis: movement of water (solvent) across semi-permeable membrane • Osmolarity: total solute concentration in solution • If total solute concentration differs between 2 compartments (like across membrane) water concentration differs too – Water moves from high water (low solute) to low water (high solute): • Some directly through PM • Most through aquaporins (H20 channels) – Cell remains same size

Question 101

Osmotic pressure

Answer 101

tendency of water to move in or out of cell (or solution in a compartment) by osmosis, pulling force solute has on water – Water moves from high to low H20 conc., moves towards more solute • Side A above with more solute/less H20 has higher osmotic pressure • Higher non-moving [solute]= higher osmotic pressure • Water moves towards higher osmotic pressure (towards higher solute) • In normal body conditions: osmotic pressure inside cell =outside cell

Question 102

Osmosis in physiology

Answer 102

• Isotonic solution (normal condition) *inside and outside cell = 2 compartments! – Same solute conc. in outside solution vs. inside cell (same osmotic pressure)- cells do not shrink or swell – No net osmotic flow – Cell maintains “tone” • Hypotonic solution – Less solute in outside solution vs. inside cell – Water flows into cell toward higher solute – Cells swell: can burst • Hypertonic solution – More solute outside than inside cell – Water flows out of cell towards higher solute – Cell shrinks

Question 103

Isotonic solution

Answer 103

(normal condition) *inside and outside cell = 2 compartments! – Same solute conc. in outside solution vs. inside cell (same osmotic pressure)- cells do not shrink or swell – No net osmotic flow – Cell maintains “tone”

Question 104

Hypotonic solution

Answer 104

– Less solute in outside solution vs. inside cell – Water flows into cell toward higher solute – Cells swell: can burst

Question 105

Hypertonic solution

Answer 105

– More solute outside than inside cell – Water flows out of cell towards higher solute – Cell shrinks

Question 106

Fluid shifts and water balance

Answer 106

• Remember! Water moves to compartment with more solute • Dehydration • Overhydration (“Water intoxication”) • Don’t drink salt water if stranded at sea! Why?

Question 107

Active transport: not so easy

Answer 107

• Movement of solute from low to high concentration (against gradient) or vesicle involved: primary or vesicular transport – Uses energy • Primary active transport – Energy required: ATP used directly – Carrier protein needed: ion pumps – Move ion/molecule against/up concentration gradient (low to high) • Make gradient even higher • Na+, K+, Ca2+ ,Mg2+ ,Cl- • Can transport 1 or >1 ion at time – Transport influenced by: • Pump number • ATP supply

Question 108

Primary active transport example!

Answer 108

• Na+ /K+ exchange pump: Most important to cell! – Example of ion exchange pump – This one transports > 1 ion, in opposite directions – Moves ions against concentration gradient • 3 Na+ out for 2 K+ in – Requires ATP hydrolysis (energy source) – Maintains HIGH extracellular Na+ and HIGH intracellular K+ – CRITICAL for homeostasis

Question 109

Gradients across the membrane

Answer 109

• These transport processes create/maintain differences across membrane • Electrochemical gradient : electrical & chemical difference across the membrane – Result of membrane selective permeability and transport processes – Represents stored energy – Components: Gradients across the membrane • Electrical gradient: Transmembrane potential – Resting membrane potential of cells: negative inside – Due to more – charged proteins and fewer + charged ions in cell • Concentration (chemical) gradient: ie. more Na+ outside and more K+ inside

Question 110

Vesicular transport (bulk transport)

Answer 110

• Materials move into or out of cell in sacs that bud off membranes (vesicles) • Requires ATP • Types: – Endocytosis: substance brought from outside to inside cell • Phagocytosis • Pinocytosis – Exocytosis: substance released from inside to outside cell

Question 111

Endocytosis

Answer 111

substance brought from outside to inside cell • Phagocytosis • Pinocytosis

Question 112

Exocytosis

Answer 112

substance released from inside to outside cell

Question 113

Endocytosis

Answer 113

• Vesicle formation requires energy • Phagocytosis: – “cell eating”: large particles – Select cells: phagocytes – Surrounds with pseudopods • Forms vesicle: phagosome • Digests when fuses with lysosome • Pinocytosis: – “cell drinking”: small vesicles – Bring in interstitial fluid with dissolved molecules – Most cells capable

Question 114

Endocytosis

Answer 114

• Receptor-mediated endocytosis – Very selective! • Substance brought in must binds specific receptor on surface of cell – For example: cholesterol uptake from blood into cell

Question 115

Exocytosis

Answer 115

• Vesicle fuses with plasma membrane – requires energy • Contents released (secreted) – Secretion of hormones, digestive enzymes, neurotransmitters • Helps to also recycle and replace membrane to balance endocytosis