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BIOSCI 107 > Section 2: Cell Structure & Function > Flashcards

Section 2: Cell Structure & Function Flashcards

1
Q

Central dogma

A

DNA –transcribed–> RNA –translated–> Protein
DNA: heritable material
RNA: intermediary / messenger
Proteins: workers

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2
Q

Prokaryote vs eukaryote cell

A 
Both have:
Plasma membrane
Cytosol
DNA
RNA
Protein
Ribosomes

Eukaryotic cells:
Membrane-bound organelles
Much larger

Prokaryote cells:
Lack membrane-bound nucleus

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3
Q

Cytoplasm - description + major organelles

A

Everything inside the plasma membrane except for the nucleus

Endomembrane system
Mitochondria
Ribosomes

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4
Q

Endomembrane system

A 
Consists of:
Nucleus
Endoplasmic reticulum (smooth and rough)
Golgi apparatus
Lysosomes

Along with plasma membrane, they work together to package, label, and ship molecules

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5
Q

Plasma membrane

A

A selectively permeable barrier controlling passage of substances in and out of cell
Double layer of phospholipids with embedded proteins
Physical barrier separating inside and outside of cell

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6
Q

Body and fats - hydrophilic and hydrophobic

A

Much of our body is hydrophilic (water-loving)
Fats are hydrophobic (water-hating), so tend to cluster together to exclude water
Fats in cell membrane provide barrier to water

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7
Q

Phospholipid

A

Hydrophilic polar heads (phosphate)
Hydrophobic lipid tails (fatty acids)
Arranged as double layer around cytoplasm - tail to tail
2 sheets/double layer naturally forms a water-excluding membrane

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8
Q

Plasma membrane proteins

A

Mediate movement of hydrophilic substances
Often amphipathic
Allow cell-cell identification and facilitate intercellular communication
Some proteins may form channels - a pathway through the protein for hydrophilic things to go through

Integral proteins
Peripheral membrane proteins

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9
Q

Define amphipathic

A

Have both hydrophilic and hydrophobic regions

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10
Q

Integral proteins

A

Embedded (partially or fully) into membrane

Transmembrane: goes through both layers of cells

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11
Q

Peripheral membrane proteins

A

Associated with membrane, but not actually embedded in it

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12
Q

What plasma membrane proteins do, i.e. types of plasma membrane proteins

A

Transport - channels may be general or selective, gated or not, passive or require energy
Enzymatic activity - carry out chemical reaction, may be part of a team of enzymes
Signal transduction - external signaling molecule causing transduction of information to inside of cell
Cell-cell recognition - use of glycoproteins as molecular signatures of extracellular side of cell
Intercellular joining - e.g. junctions
Attachment to cytoskeleton and ECM - e.g. fibronectin mediates contact between cell surface integrins and ECM facilitates movement

Cell-specific (spatial) and dynamic (temporal) repertoire of membrane-bound proteins: depends on job of cell, and what’s happening in the cell at that time

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13
Q

Glycoproteins

A

Carbohydrate + protein

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14
Q

Fluid Mosaic model

A

The membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids

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15
Q

Nucleus

A

Largest organelle
Enclosed by nuclear envelope
Entry and exit through nuclear pores

Functions:

  • House/protect DNA in eukaryotic cells
  • Make RNA and assemble ribosomes
  • Nucleus and cytoplasm separate –> molecule segregation to allow temporal and spatial control of cell function
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16
Q

Nuclear envelope

A

Double lipid bilayer

Continuous with rough ER

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17
Q

Nucleolus

A

rRNA production

Assembly of small and large subunits of ribosomes

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18
Q

In the nucleus: DNA (deoxyribonucleic acid)

A

The nucleic acid that encodes phenotype

Must be packed to fit into nucleus:
DNA wrapped 2x around group of 8 histones to form nucleosomes, collectively known as chromatin
As cell prepares for cell division, condenses further to chromatin fiber then condenses further into loops then stacks as chromosomes
Most of the time, DNA present as chromatin and chromatin fibres

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19
Q

Chromosome

A

Comprised of many genes

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20
Q

Gene

A

A DNA segment that contributes to phenotype/function

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21
Q

Humans - diploid

A

2N = 46
23 pairs of chromosomes, one from each parent
22 autosomes, 2 sex chromosomes

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22
Q

Packaging of nucleus

A

All DNA in one cell stretches out to ~2m
Accessibility determined by extent of coiling
Condensed chromosomes easier to organize than chromatin

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23
Q

Ribosomes

A

2 subunits, small and large made of rRNA in complex with many proteins
No membrane - would be inefficient

Function: protein production
Found in 2 places within cell:
- Free in cytoplasm - making proteins to be used in cytosol
- Attached to rough ER - making non-cytosolic proteins/endomembrane

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24
Q

rRNA

A

Ribosomal RNA

Subunits assemble in nucleolus, leave through nuclear pores

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25
Q

Endoplasmic reticulum

A

An extensive network of tubes and tubules, stretching out from nuclear membrane/envelope
Two types: rough and smooth

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26
Q

Rough ER

A

Continuous with nuclear envelope
Dotted with attached ribosomes

Main function is production of:
Secreted proteins
Membrane proteins
Organelle proteins

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27
Q

Rough ER - proteins

A

Proteins enter lumen within rough ER for folding

Rough ER membrane surrounds protein to form transport vesicles destined for golgi

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28
Q

Smooth ER

A

Extends from rough ER
Lacks ribosomes - doesn’t make proteins

Major function:
Housing unit for proteins and enzymes
Synthesizes lipids
Storage of cell-specific proteins (not all cells make all proteins)
Produces sex hormones
Functions vary greatly from cell to cell - very cell/tissue-type specific

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29
Q

Golgi apparatus/complex/body - description, function, formation of…

A

The ‘warehouse’
Made up of 3-20 cisternae, stacked on top of one another

Modify, sort, package and transport proteins received from rough ER using enzymes in each cisternae
Responsible for exocytosis of proteins from cell

Formation of:
Secretory vesicles (proteins for exocytosis)
Membrane vesicles (PM molecules)
Transport vesicles (molecules to lysosome)
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30
Q

Cisternae

A

Flattened membranous sacs

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31
Q

Secretory cells have…

A

Extensive golgi complexes, e.g. goblet cells

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32
Q

Golgi apparatus: to destination

A

Each cisternae contains enzymes of different functions

Proteins move cis to trans from sac to sac
Mature at the exit cisternae
Travel to destination

Modifications occur within each sac (formation of glycoproteins, glycolipids and lipoproteins

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33
Q

Lysosomes

A

Contain powerful digestive enzymes
Vesicles formed from golgi body
Membrane proteins pump H+ in to maintain acidic pH

Main function is digestion of:
- Substances that enter a cell
- Cell components, e.g. organelles - autophagy
- Entire cells - autolysis
Once digested, all building blocks are recycled

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34
Q

Lysosomal storage disorders

A

Failure of a single lysosome enzyme can cause severe disease

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35
Q

Gaucher metabolic disorder

A

Lysosomal storage disorder
A particular lipid (glucocerebroside) is poorly degraded
Results in severe phenotype in humans

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36
Q

Mitochondria - main function

A

Generation of ATP through cellular respiration

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37
Q

Mitochondria are made up of…

A

Outer mitochondrial membrane
Inner mitochondrial membrane, with folds called cristae
Fluid filled interior cavity, called mitrochondrial matrix

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38
Q

Mitochondria and energy

A

The more energy a cell requires, the more ATP it must make, the greater number of mitochondria present

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39
Q

Transfer of phosphate to another molecule provides ______

A

Energy

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40
Q

ATP

A

Adenosine triphosphate - our energy currency

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41
Q

Cytoskeleton

A

Structural support system of cell
Fibres of filaments that help to maintain the size, shape, and integrity of the cell:
- Act as scaffolding across cell
- Involved in intracellular transportation and cell movement

Three types of fibers (smallest to largest):
Microfilaments (dynamic - assembled and disassembled as required)
Intermediate filaments
Microtubules (dynamic)

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42
Q

Cytoskeleton: Microfilaments - description

A

Diameter: 7nm
Comprised of actin molecules assembled in two long chains, twisted around each other
Found around periphery and lining the interior of cell

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43
Q

Cytoskeleton: Microfilaments - functions

A

Bear tension and weight by anchoring cytoskeleton to plasma membrane proteins
Promote amoeboid motility if required, e.g. macrophage

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44
Q

Cytoskeleton: Intermediate filaments - description

A

Diameter: 8-12nm
Comprised of diverse range of different materials, e.g. keratin
Found in cytoplasm of cell
Often the most permanent of cytoskeleton

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45
Q

Cytoskeleton: Intermediate filaments - functions

A

Bear tension and weight throughout cell

Act as scaffold for cellular organelles

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46
Q

Cytoskeleton: Microtubules - description

A

Diameter: tubular structure, 25nm with central lumen of 15 nm diameter
Comprised of tubulin dimers (alpha and beta), coiled, to form a tube
Extends from centriole into cytoplasm/nucleus

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47
Q

Cytoskeleton: Microtubules - functions

A

Support cell shape and size
Guide for movement of organelles, e.g. vesicles from Golgi to membrane
Chromosome organisation - cell division
Support and movement of cilia/flagella

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48
Q

Energy process

A

ATP –> ADP –> Phosphate (transferred to another molecule)

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49
Q

Major categories of fuel

A

Carbohydrates - broken down to simpler sugars
Proteins - broken down to amino acids
Fats - broken down to simple fats

Which are then absorbed

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50
Q

Main steps of cellular respiration

A

Glycolysis (cytosol)
Pyruvate oxidation (mitochondrial matrix)
Citric acid/Krebs cycle (mitochondrial matrix)
Electron transport chain and chemiosmosis (oxidative phosphorylation) (proteins within inner membrane)

C6H12O6 + 6O2 –> 6CO2 + 6H2O + Energy

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51
Q

Electron transport chain - FADH2 and NADH

A

FADH2 and NADH are electron donors in the electron transport chain

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52
Q

Citric acid cycle intermediates

A

Used in other metabolic pathways
A series of reactions: product of first reaction is the substrate for the next

Acetyle CoA –> Citrate –> α-Keto-glutarate –> Succinyl CoA –> Malate –> Oxaloacetate (cycle)

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53
Q

Substrate phosphorylation

A

ATP is generated by direct transfer of a phosphate group to ADP
Glycolysis and citric acid cycle make ATP via this process

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54
Q

Oxidative phosphorylation

A

ATP is generated from oxidation of NADH and FADH2 and the subsequent transfer of electrons and pumping protons

ETC and chemiosmosis

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55
Q

Oxygen and cyanide

A

Oxygen is the final electron acceptor

Cyanide blocks passage of electrons to O2 = death of cell

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56
Q

Cellular respiration is versatile

A

Energy can be derived from more than just glucose
Fats, proteins, and more complex carbohydrates also generate ATP
Monomers enter glycolysis and citric acid at different points

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57
Q

Control of cellular respiration - phosphofructokinase

A

Can limit rate of glycolysis
Inhibited by citrate and ATP, i.e. products of cellular respiration
Stimulated by AMP - accumulates when ADP not phospho to ATP

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58
Q

Control of cellular respiration - feedback

A

Negative feedback control is integral to control ATP production
Homeostasis generally depends on negative feedback mechanisms, but can be impacted by on positive feedback mechanisms

Negative feedback: more results in less, e.g. blood glucose
Positive feedback: more results in more e.g. blood clotting

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59
Q

Homeostasis - increasing blood glucose level

A

Receptors - beta cells in pancreatic islets –>
Secrete insulin –>
Effectors - all body cells –respond with–>
Increased rate of glucose transport into target cells,
increased rate of glucose use and ATP generation,
increased conversion of glucose to glycogen –>
Homeostasis restored by decreasing blood glucose level

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60
Q

Homeostasis - decreasing blood glucose level

A

Receptors - alpha cells in pancreatic islets –>
Secrete glucagon –>
Effectors - liver, skeletal muscle, adipose cells –respond with–>
Increased breakdown of glycogen to glucose (in liver, skeletal muscle) –>
Homeostasis restored by increasing blood glucose level

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61
Q

Homeostasis of blood glucose - produced by? and function?

A

Insulin:
Produced by beta cells of islets of Langerhans in pancreas
Function - promote glucose uptake into cells (for ATP production or storage in liver)

Glucagon:
Produced by alpha cells of islets of Langerhans in pancreas
Function - stimulates breakdown of glycogen to increase blood sugar levels

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62
Q

What happens if you lose the function of insulin

A

No glucose in cells
No ATP from glucose
No glycogen for ‘harder times’

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63
Q

Diabetes mellitus

A

The ability to produce or respond to the hormone insulin is impaired
Results in abnormal metabolism of carbohydrates and elevated levels of glucose in blood
Symptoms: vision changes, fatigue, frequent urination, tingling hands/feet

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64
Q

Carbohydrates broken down to…

A

Simple sugars through digestive system

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65
Q

What is NADH

A

An electron carrier

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66
Q

Purpose of electron carriers

A

Transport electrons, e.g. to reactions in mitochondria

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67
Q

Glucose can transfer across ____ into ______

A

Membranes into bloodstream

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68
Q

Where is glycogen typically stored

A

Liver and skeletal muscles

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69
Q

How many ATPs per second in one cell does cellular respiration generate?

A

10 million ATPs per second

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70
Q

Glucagon vs glycogen

A

Glucagon acts on glycogen

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71
Q

Lipid chain length

A

Can be different lengths –> dictates fluidity of membrane

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72
Q

Lipid chain saturation

A

Can be saturated or unsaturated –> dictates structure

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73
Q

Nuclear pores

A

Channels; tightly regulated

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74
Q

Plasma membrane - hydrophobic or hydrophilic

A

Part of protein inside membrane must be hydrophobic so they’re able to interact and pass through the hydrophobic part of membrane
Part of protein outside membrane must be hydrophilic as they will be interacting with water

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75
Q

Chromatin vs chromosomes

A

If wanting to make RNA and proteins, must be able to access - hard to access large portions of genome (in chromosome), so easier to access chromatin as it’s slightly more relaxed

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76
Q

Without functioning free ribosomes…

A

Production of proteins destined for use in cytoplasm would be impaired

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77
Q

Without a functioning Golgi apparatus…

A

Protein modification would be impaired

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78
Q

Without functioning lysosomes…

A

Autophagy and autolysis would be impaired

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79
Q

Genotype vs phenotype

A

Genotype: an organism’s hereditary information
Phenotype: actual observable or physiological traits

Our genotype and its interaction with the environment determines our phenotype

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80
Q

Gene expression

A

The process of going from DNA to a functional product (typically protein)
Highly regulated - not by chance, doesn’t occur spontaneously

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81
Q

DNA

A

The heritable material that is used to store and transmit information from generation to generation

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82
Q

RNA

A

Acts as a messenger to allow info stored in DNA to be used to make proteins

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83
Q

Proteins carry out…

A

Cellular functions

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84
Q

Gene expression - main steps

A

Transcription of RNA from DNA
Processing of pre-mRNA transcript into mature mRNA
Translation of mRNA transcript to a protein

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85
Q

Gene expression - types of proteins

A

Housekeeping (commonly used) proteins:
Continuously produced from DNA
Protein and mRNA present in large quantities (e.g. tubulin)
Typically have long half life in cells

Other proteins produced in response to stimuli as required:
Cell signalling (e.g. ligand binding a cell surface receptor, or activating an intracellular receptor)
Signal transduced and may enter nucleus to active transcription
Results in production of a short-lived protein to carry out the required function

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86
Q

Transcription - main steps

A

Initiation - polymerase binds to promoter
Elongation - moves downstream through gene transcribing RNA
Termination - detaches after terminator reached

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87
Q

DNA vs RNA bases

A

DNA: A, T, C, G
RNA: A, U C, G

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88
Q

Exons

A

Coding regions (inc UTRs)

89
Q

Introns

A

Non-coding regions intervening exons

90
Q

UTR

A

Untranslated regions at 5’ and 3’ ends

End up in mature mRNA but not part of protein

91
Q

Spliceosome

A

A large complex of proteins and small RNAs

92
Q

Alternative splicing

A

A process by which different combinations of exons are joined together, resulting in the production of multiple forms of mRNA from a single pre-mRNA
Allows for multiple gene products from the same gene

93
Q

Protein sequence determines…

A

Amino acid final structure

Structure determines function

94
Q

Translation: main steps

A

Initiation
Elongation
Termination

95
Q

How do codons form amino acids

A

Codons are translated into amino acids

96
Q

Where is tRNA and mRNA held

A

Within ribosomes to enable the formation of polypeptides

97
Q

Ribosome binding sites

A

mRNA binding site
A site - holds ‘next-in-line’ tRNA
P site - holds tRNA carrying the growing polypeptide
E site - tRNAs exit from here

98
Q

tRNA

A

The physical link between mRNA and amino acid sequence of proteins

99
Q

Initiation tRNA

A

tRNA carrying methionine (Met)

100
Q

Translation - elongation

A

Codon recognition
Peptide bond formation
Translocation

101
Q

How are properties of amino acids determined

A 
Side chains (R groups) determine properties of each amino acid
20 standard amino acids
102
Q

Amino acids - primary structure

A 
Determined by DNA sequence
Held by covalent bonds between amino acids (strongest bonds out of all structures)
Starts to form secondary structures as soon as it leaves the ribosome
Reads N (amino end) to C (carboxyl end)
103
Q

Amino acids - secondary structures are held by…

A

Held by weak H bonds to form alpha helix and beta sheets

104
Q

Amino acids - tertiary structures

A

3D shape stabilised by side chain interactions

105
Q

Amino acids - quaternary structures

A

Multiple proteins associate together to form a functional protein
(not all proteins do this, but all form secondary and tertiary structures)

106
Q

Where is the signal peptide found

A

At N terminus of protein

107
Q

SRP

A

Signal Recognition Particle

108
Q

What happens when completed polypeptide folds into final conformation

A

A secretory protein (e.g. insulin) is solubilised in lumen, while a membrane protein remains anchored to the basement. Both then go to the Golgi via vesicles for further maturation

109
Q

Signal peptides direct ribosomes to RER - steps

A
  1. Polypeptide synthesis begins
  2. SRP binds to signal peptide
  3. SRP binds to receptor protein
  4. SRP detaches and polypeptide synthesis resumes
  5. Signal-cleaving enzyme cuts off signal peptide
  6. Completed polypeptide folds into final conformation
110
Q

Post-translational modifications

A

Where translation is complete, but protein may not yet be functional
e.g. Phosphorylation
Some occur within Golgi, others in cytosol
Modification errors could lead to non-functional proteins

111
Q

What can post-translational modifications do

A 
Confer activity (e.g. phosphorylation or enzyme cleavage)
Ability to interact with other molecules (e.g. biotinylation, methylation)
Direct to particular locations (e.g. ubiquitination)
112
Q

Mutations can affect…

A

The structure and function of a protein

113
Q

DNA level mutations can affect…

A

50-100% of downstream products from cells carrying that mutation (because we have two alleles)

114
Q

Types of effects of altered DNA sequence

A

Minor, none, or positive

Germ line - can affect many cells and be catastrophic
Local - during cell division, not whole body - local effects

115
Q

Large vs small scale alterations

A

Large - chromosomal rearrangements

Small - one or a few nucleotides altered

116
Q

Point mutations can be…

A

Substitutions - where one base is replaced by another; can have minimal or major effect
Insertions/deletions - can cause a frameshift; can have major effect if within coding sequence

117
Q

Polypeptide

A

Made up of many peptides

118
Q

Promoters vs terminators

A

Promoters - upstream

Terminators - downstream

119
Q

Which way does DNA read

A

From 5’ to 3’ end
Template strand (3’ to 5’) used so it can create a 5’ to 3’ RNA
Non-template strand 5’ to 3’

120
Q

TATA box

A

A particular protein to a particular sequence within the promoter
Transcription initiation complex

121
Q

RNA polymerase

A

Makes polymer of RNA
During termination of transcription, RNA polymerase catalyses phosphate diester bonds, which makes RNA stay together when coming off as a single strand

122
Q

Phosphor-diester bonds - purpose

A

Hold RNA together

123
Q

Proteins - isoforms

A

Most proteins that exist don’t only have one version of themselves - often have different isoforms

124
Q

Codon

A

3 codons from mRNA = 1 amino acid

125
Q

Mutations in DNA change…

A

Change shape of resulting protein –> change ability to do its job

126
Q

tRNA shape

A

Looped structure, where one of the loops forms an anti-codon which binds to the relevant mRNA codon

127
Q

What is tRNA

A

The physical link between mRNA and the protein sequence

128
Q

Start and stop codon(s)

A

Start codon: AUG
Stop codons: UAG, UAA, UGA
Must be in frame

129
Q

Bonds between amino acids

A

Ribosomes help form covalent bonds between amino acids

130
Q

Types of amino acid proteins

A

Hydrophobic
Hydrophilic
Hydrophilic - negatively charged
Hydrophilic - positively charged

131
Q

Translation - endomembrane system

A

Vesicles are transferred from one part of the endomembrane system to another, and eventually end up on plasma membrane

132
Q

How do free ribosomes know when they need to be in rough ER?

A

At the end of terminus, there’s a signal peptide which can be detected by SRP, which tells the peptide it needs to be made in RER

133
Q

What happens if transcription doesn’t function properly

A

If transcription was on strike in ONE CELL within a tissue, there would be no RNA made from that cell
OR
If transcription had not quite enough for ONE TRANSCRIPTION FACTOR, then likely other transcripts are still made in that cell. Not enough, but can be compensated

134
Q

If folding happened incorrectly…

A

Protein may not be able to function normally

Depends on scale of error - might not be catastrophic

135
Q

What is found in cytosol?

A

Organelles, water, dissolved solutes, suspended particles

136
Q

What is cytosol also known as

A

Intracellular fluid

137
Q

Apoptosis

A

Programmed cell death

138
Q

Oxidation reactions can produce…

A

Hydrogen peroxide (H2O2), which can be broken down by catalase to form H2O in peroxisomes

139
Q

Why do cells communicate

A

They need to be able to respond as a cell, and as part of a whole tissue
They respond to signals from other cells and from the environment

Signals are often chemical, but can also be light, taste, smell etc.

140
Q

Types of secreted signals

A

Local signalling

Long distance signalling

141
Q

Secreted signals - local signalling

A

Signals act on nearby target cells

  • growth factors such as fibroblast growth factor (FGF1 - paracrine)
  • neurotransmitters such as acetylcholine (Ach - synaptic)
142
Q

Secreted signals - long distance signalling

A

Signals act from a distance
- hormones produced by specialised cells travel via circulatory system to act on specific cells
- e.g. insulin from pancreatic beta cells bind to insulin receptors, initiating a cascade, resulting in glucose uptake
Endocrine system

143
Q

Cell signalling - main steps

A

Reception
Transduction
Response

144
Q

Receptors are _____

A

Specific
Human body simultaneously sends out many different chemicals and molecules, all aimed at eliciting specific responses, BUT only the target receptor on the target cell will interact with that signal/ligand and use it to activate signal transduction pathways

145
Q

Where does the specificity of receptors come from?

A

3D molecular shape of proteins involved

Structure determines function

146
Q

Exquisite control of receptors is possible

A

Only certain cells at certain times will have the particular receptors, so while the signal might be widespread, the transmission of the signal only occurs where needed

147
Q

Main types of receptors

A

Intracellular receptors

Membrane-bound/cell surface receptors

148
Q

Intracellular receptors

A

Primary messenger is generally hydrophobic and/or small - lipid soluble, can cross PM
Least common method of signalling

e.g. testosterone, estrogen, progesterone, thyroid hormones bind to receptors in cytoplasm and move to nucleus as a complex

149
Q

Membrane-bound / cell surface receptors

A

Primary messenger is generally hydrophilic and/or large - need help to cross PM
Most common method of signalling

e.g. G protein coupled receptor, ligand-gated ion channel, receptor tyrosine kinase

150
Q

G-protein coupled receptors (GPCRs)

A

Transmembrane proteins - pass PM 7 times
Hundreds of different GPCRs exist
Many different ligands
Diverse functions, e.g. development, sensory reception

151
Q

G proteins

A

Molecular switches either on or off depending on whether GDP or GTP is bound

152
Q

G-protein coupled receptors - steps

A
  1. At rest, receptor is unbound and G-protein is bound to GDP. Enzyme is in an inactive state.
  2. Ligand binds receptor (causing conformational shape change), and binds G protein. GTP DISPLACES GDP. Enzyme is still inactive. Shape alters.
  3. Activated G protein dissociates from receptor. Enzyme is activated to elicit a cellular response
  4. G protein has GTPase activity, promoting its release from enzyme, reverting back to resting state.
153
Q

GPCRs - what determines function?

A

Conformational changes determine function

154
Q

Which body system relies heavily on ligand gated ion channels?

A

The nervous system

- released neurotransmitters bind as ligands to ion channels on target cells to propagate action potentials

155
Q

Protein kinases

A

Enzymes that transfer a phosphate group from ATP to another protein
Typically, this activates the protein

156
Q

Signal transduction pathways

A

Signals can be relayed from receptors to target molecules within the cell via a ‘cascade’ of molecular interactions
e.g. series of protein kinases each adding a phosphate to the next kinase

Activates protein kinase which was inactive
Active 1 activates inactive 2, etc.
Last one in pathway of kinases is able to activate an inactive protein, which is then able to confer the actual cellular response

157
Q

Phosphatases

A

Enzymes that dephosphorylate (remove phosphate), rendering the protein inactive, but recyclable

158
Q

What are typically phosphorylated?

A

Serine or threonine

This means mutations affecting these residues could be detrimental

159
Q

Second messengers

A

Another small molecule included in the cascade, e.g. cAMP and Ca2+

160
Q

Second messengers- cAMP

A

Links to GPCR
Activated enzyme is adenylyl cyclase
Activated adenylyl cyclase converts ATP to cAMP
cAMP acts as a second messenger and activates downstream protein (coud be start of a phosphorylation cascade)

161
Q

Second messenger - calcium

A

Low Ca2+ conc inside cell
High Ca2+ conc outside cell

Maintenance of conc via calcium pumps is important as high Ca2+ conc can damage cells

  • out of cell
  • into ER
  • into mitochondria
162
Q

Ca2+ and IP3 in GPCR signalling

A

Activated protein is phospholipase C, which cleaves PIP2 (phospholipid) into DAG and IP3
IP3 diffuses through cytosol and binds to a gated channel in ER
Calcium ions flow out of ER, down conc gradient, and activate other proteins towards a cellular response

163
Q

Many steps in cellular signalling because…

A

Amplifies the response
Provides multiple control points
Allows for specificity of response (temporal, spatial) despite molecules in common
Allows for co-ordination with other signalling pathways

164
Q

Cellular response includes activation or regulation of…

A

Gene expression

165
Q

Turning off cellular responses

A

All signals are for a limited time; activation usually promotes start of deactivation so that signal is of short period of time, ensuring homeostatic equilibrium
Cell ready to respond again if required
cAMP broken down by phosphodiesterase (PDE)

166
Q

Glycogen

A

A long term energy store in liver and skeletal muscle
Glycogen breakdown results in glucose 1-phosphate
Glucose 1-phosphate is then converted to glucose 6-phosphate, which can be used in glycolysis to generate ATP

167
Q

Paracrine vs synaptic signalling

A

Paracrine: where cell releases signals to target nearby cells, e.g. blood clotting
Synaptic: similar to paracrine signalling, but only occurs between cells with synapse

168
Q

Somatic cell division

A

Mitosis

Diploid (2n) to diploid (2n)

169
Q

Reproductive cell division

A

Meiosis

Diploid (2n) to haploid (1n)

170
Q

Why do somatic cells divide

A

Growth and development, tissue renewal

Results in two daughter cells genetically identical to the parent cell

171
Q

Do all somatic cells divide

A

Most, but not all, some a lot more than others

e.g. muscle cells don’t divide

172
Q

What are somatic cells doing most of the time

A

Going about their functions in G1 of interphase

173
Q

Eukaryotic cell cycle - mitotic phase

A 
Mitosis + cytokinesis
Prophase (early and late)
Metaphase
Anaphase
Telophase and cytokinesis
174
Q

When does cytokinesis begin

A

Anaphase, where it starts to pinch in

175
Q

Mitosis - daughter cells

A

Genetically identical to parent cell

2n to 2n

176
Q

Key regulatory molecules for G2 checkpoint

A

Cyclin: a protein that fluctuates throughout the cell cycle
Cyclin dependant kinase (Cdk): a kinase that is activated when attached to a cyclin
M-phase promoting factor (MPF): a cyclin/Cdk complex - phosphorylates many other proteins, allowing mitosis to commence

177
Q

G1 checkpoints

A

Checks if:
DNA is undamaged
Cell size and nutrition is okay
Appropriate signals are present

If not - exit to G0

178
Q

M checkpoints

A

Checks if all chromosomes are attached to signals
Within mitosis itself
Final point prior to anaphase and telephase

179
Q

Checkpoints of cell cycle rely on…

A

Cell signalling

180
Q

What could happen if cell cycle checkpoints don’t work

A

Could result in uncontrolled cell growth –> tumours

181
Q

DNA changes can be…

A

Small scale alterations (point mutations)

Gain/loss/translocation of chromosomes/genes

182
Q

DNA changes can be the result of…

A

Acquired changes:
Affects specific cells
Viruses, UV damage, drugs, treatments

Inherited changes:
Affects all cells
Susceptibility genes

In both acquired and inherited DNA changes, altered protein function can result, which may lead to loss of cell cycle control

183
Q

In cancer, genes affected by DNA changes are often…

A

Proto-oncogenes:
Genes that stimulate cell proliferation
Pressing the ‘accelerator’
Activation

Tumor suppressor genes:
Genes that keep proliferation in check
Loss of ‘brakes’
Deactivation

Both result in uncontrolled cell growth (tumour)

184
Q

Meiosis

A

Occurs in gonads
Produces gametes which are haploid (single set of 23 chromosomes)
Fertilisation then restores the diploid number of chromosomes (2n)
Produces genetically different daughter cells from parent cell

185
Q

Stages of meiosis

A

Meiosis I:
Prophase I (synapsis and crossing over, tetrads form)
Metaphase I (pairs of homologous chromsoomes)
Anaphase I (sister chromatids remain attached)
Telophase I

Meiosis II:
Prophase II
Metaphase II
Anaphase II
Telophase II
186
Q

Meiosis II vs mitosis

A

Very similar, except meiosis II is not preceded by DNA replication

187
Q

Sources of genetic variation

A

Independent assortment at metaphase I
Crossing over at prophase I
Fusion between two gametes

188
Q

How would you sample for DNA from tumours

A

Isolate the DNA from the tumour itself

189
Q

Coronavirus lock and key

A

ACE2: Angiotensin-converting enzyme 2 -
cellular receptor
S protein: Surface spike glycoprotein (S protein)
ACE2 in our respiratory tract is the lock, S-protein on the virus is the key

190
Q

How does DNA polymerase III enter the nucleus from the outside

A

Primary active transport

191
Q

A frequent problem in cancer cells is that cell division happens without the chromosomes being fully packed. This could be a problem with the formation of…

A

Nucleosome, chromatid, or chromatin fibres

192
Q

Improperly formed intermediate filaments cause…

A

Abnormally shaped nuclear envelope

193
Q

What cells have multiple nuclei

A

Skeletal muscle cells

194
Q

Nucleolus is formed by…

A

DNA, RNA and proteins

195
Q

Water molecules that move into the nucleus enter via…

A

Passive diffusion

196
Q

When are chromatids found in a cell

A

Just prior to and during cell division

197
Q

What do you find between nucleosomes

A

Linker DNA

198
Q

Where does transcription and translation occur

A

Transcription: nucleus
Translation: ribosomes

199
Q

Pathway from production to membrane insertion of Na+ channel?

A

Translation on rough ER –> transport vesicle –> Golgi complex –> secretory vesicle –> plasma membrane

200
Q

To have an increase in protein production, there is likely to be an increase in…

A

Transcription of oncogenes in the nucleus

201
Q

In a phosphorylation cascade, protein kinases ____ proteins by ______ them, while
phosphatases _____ proteins by ______ them

A

activate, phosphorylating, inactivate, dephosphorylating

202
Q

Why people feel ‘wired’ after coffee

A

Caffeine blocks the action of a phosphodiesterase which breaks down a second messenger released after adrenalin activation

203
Q

Sickle cell disease - DNA mutation

A

Substitution

204
Q

Which protein is often mutated in cancer cells

A

RAS (type of proto-oncogene)

205
Q

Mutated tumour suppressor protein

A

If DNA replication is incomplete and protein is activated at G2 checkpoint, but cell progresses to enter M phase, activated protein is most likely to be a mutated tumour suppressor protein

206
Q

Efferent pathway

A

Information flowing away from the control centre

207
Q

Synovial fluid

A

ECM found in joints

208
Q

Nervous system regulates homeostasis in the body through _____

A

Neurotransmitters

209
Q

Cytokinesis

A

Division of cytoplasm

Happens after mitosis / meiosis I

210
Q

Cleave furrow is formed by which cytoskeleton?

A

Microfilaments

211
Q

S phase time

A

The replication of chromosomes in S phase takes a specific amount of time that can’t be increased

212
Q

Brush border refers to…

A

Microvilli

213
Q

The initial structure formed as a polypeptide synthesised in a ribosome is…

A

A polypeptide chain of unbranched polymers, held tightly together by peptide bonds

214
Q

Insulin is secreted by…

A

Endocrine cells

215
Q

Which part of skin are fibroblasts found

A

Dermis - not epidermis

216
Q

Which fibrous protein commonly forms part of the cytoskeleton of the cell

A

Keratin

217
Q

Which structure of the cell stores the second messenger critical for muscle contraction

A

Smooth ER

218
Q

If a protein is recognised by a Signal Recognition Particle…

A

That protein might function in the fluid of the extracellular matrix, as protein is sorted via the cisternae of the Golgi complex because of the SRP

BIOSCI 107 (7 decks)

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