Lecture 6 Flashcards by Ja Ja

Basic information of cells/Cell theory

All living organisms are composed of one or more - cells
The cells is the basic unit of structure and organisation
All cells arise only from pre-existing cells
Cells are small due to the balance between surface area and size

Universal similarities between cells:
- DNA as the heritable material, RNA as a messenger and proteins as the workers (the central dogma = DNA makes RNA which makes proteins)
- Major cellular organelles - functions and arrangements within the cell
- ATP as an energy source

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Prokaryote

Structure:
Smaller cells
Lack a membrane-bound nucleus/organelles

Both have:
Plasma membrane, cytosol, DNA, RNA, protein and ribosomes

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Eukaryote

Structure:
Larger cells, have a membrane-bound nucleus
(we are eukaryotes)

Both have:
Plasma membrane, cytosol, DNA, RNA, protein and ribosomes

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Is there a limit to cell size

Yes, most cells tend to be 10-20 microns in diameter, due to optimal balance between size and surface area

Humans have roughly 37 trillion cells

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Cytoplasm

Structure/components:
Everything inside the cell/plasma membrane including organelles but NOT the nucleus

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Cytosol

Is the fluid portion of the cytoplasm
Sturcture:
Water plus dissolved and suspended substances (ions, ATP, proteins, lipids)

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Major organelles

Nucleus (nuclear outer membrane - for
transport)
Endoplasmic Reticulum (smooth and rough)
Golgi apparatus
Lysosomes
Mitochondria
Ribosomes

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Other (non-major) organelles

Centrosome
Peroxisome

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What is included in the endomembrane system

Plasma membrane
Nucleus - more so the outer membrane
Endoplasmic Reticulum
Golgi apparatus
Lysosomes

They work together to package, label and ship molecules. Endomembrane system refers to how the membranes of the rough ER, Golgi and PM share membranes (through vesicles leaving and attaching)

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Microvilli

Smallest membrane extensions

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Cilia

Mid-sized membrane extensions

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Flagellum

Largest membrane extensions

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Plasma membrane

Structure:
Made of a bilayer of phospholipids - each phospholipid has a hydrophilic polar head (phosphate) and 2 hydrophobic lipid tails (fatty acids), and they are arranged so tails meet - with embedded proteins

Membranes are not static - they are dynamic and cell specific. The proteins which are represented in the present on a membrane change all the time.

Fluid mosaic model - membranes made of of the bilayer of phospholipids and it is constantly moving. It will have different proteins/molecules based on what is happening at the present time

Membranes of organelles have the same membrane bilayer

Functions:
Physical barrier separating inside and outside of cell

A selectively permeable barrier controlling the passage of substances in and out of cell and separating inside/outside of cell - fats in cell membrane are hydrophobic and therefore provide the barrier to water. Much of our body is hydrophilic

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What is the fluid in the cytoplasmic and extracellular areas cell made out of

Water along with other things

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What are the two types of membrane proteins?

Integral
Peripheral

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Integral proteins:

Structure:
Membrane proteins that are embedded (partially or fully) into the membrane eg. transmembrane proteins are integral membrane proteins that fully span entire membrane, contacting both extracellular and cytoplasmic areas

Often amphipathic - partially polar and partially non-polar

NOT ALL ARE TRANSMEMBRANE

Function:
Plasma Membrane proteins allow for cell-cell identification and facilitate intercellular communication

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Peripheral membrane proteins

Sturcture:
Membrane proteins that are associated with the membrane but not actually embedded in them.

Function:
Plasma Membrane proteins are often amphipathic and allow for cell-cell identification and facilitate intercellular communication

Nucleus

Structure:
Largest distinct structure inside the cell. Enclosed by a double lipid bilayer (an outer membrane and inner membrane) called the nuclear envelope
The outer membrane is continuous with the rough ER
Average size is about six microns in diameter
Nucleolus:
Make RNA and assemble ribosomes
Pores:
Regulate movement of substances eg protein and mRNA

Function:
Houses/protects DNA (DNA is there for life for that cells and can’t be replaced)
Pores allow for molecule segregation (between nucleus and cytosol) to allow temporal and spatial control of cell function (as multiple molecules in the same space may not be good)

DNA

Structure:
DNA in one cell stretches out to ~2 metres
DNA is wrapped 2x around groups of 8 histones (proteins) to form nucleosomes
Multiple of the nucleosomes are known as chromatin, and when condensed further into a rope like shape, it is called a chromatin fibre
Chromatin fibres can be looped further to produce condensed chromosomes (but they are already chromosomes when they are loose chromatin form)

When preparing for cell division, chromatin condenses to form chromatin fibres then further into loop and then stack as chromosomes - chromosomes comprises many genes (DNA segment that contributes to phenotype/function)

Each chromosome contains ~1000 genes (each gene contributes to phenotype/function of cell)

Most of the time our DNA is present as chromatin and chromatin fibres

Ribosomes

Structure:
- Made of two subunits (small and large, made from ribosomal RNA/rRNA) in complex with many proteins.
- Subunits/rRNA is made in the nucleolus which leave through the pores and later come together to form ribosome
Can be free or bound, and where they are dictates the type of protein they are making

Function:
Responsible for the translation of RNA to a protein
Free - in the cytoplasm, making proteins to be used in cytosol (non-endomembrane destinations)
Bound - on the rough ER, making non-cytosolic proteins/endomembrane

Endoplasmic Reticulum (ER)

Structure:
An extensive network of tubes and tubules, stretching out from the nuclear membrane (rough is an extension of the nucleus and the smooth comes off from the rough)

Rough ER

Structure:
Continuous with nuclear envelope, dotted with attached ribosomes,

Function:
Protein making always starts in free ribosomes, but if the protein is a secreted, membrane, or organelle protein, it will be shipped to ribosomes in the rough ER to continue being made.

The polypeptide chain will come out in the inside/lumen of the rough ER and fold

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

Smooth ER

Structure:
Has no ribosomes, doesn’t make proteins

Function:
Major function is as a housing unit for cell specific proteins and enzymes - not all cells make all proteins
Therefore function very cell and tissue specific
Synthesizes lipids, including steroids and phospholipids

Examples:
Liver: houses enzymes for detoxification and for glucose release
Muscle: calcium ions (refer ET:M)

In muscle cells have an extensive SER and the ER is called the sarcoplasmic reticulum

Golgi apparatus

Structure:
A complex made up 3-20 flattened membranous sacs called cisternae - each one has enzymes of different functions, stacked on top of one another

Part of the endomembrane system

Function:
Modifying, sorting, packaging and transporting proteins received from the rough ER using enzymes in each cisternae
Proteins move from cis (side closer to RER) to trans (side closer to plasma membrane) from sac to sac, modification occur within each sac, and mature at the exit cisternae (apparently can go round in circles)
Examples of modifications: glycoproteins, glycolipids, and lipoproteins formed here

Vesicles that leave the Golgi in a vesicles:
Secretory vesicles (proteins for exocytosis)
Membrane vesicles (PM molecules)
Transport vesicles (lysosomes)

Vesicles can allow for membrane renewal (of PM)

What cell have a lot of golgi

GOBLET CELLS HAVE A LOT OF GOLGI BECAUSE THEY MAKE MUCOUS

Lysosomes

Structure: (transport) Vesicles formed from Golgi membrane which contain inactive enzymes Are highly acidic (want to be partitioned form the cytosol/needs membrane) Membrane proteins pump H+ in to maintain acidic pH Rest of cell protected by membrane Functions: Digestion of: Substances that enter a cell Cell components e.g. (dying) organelles - autophagy Entire cells - autolysis When it fuses with another vesicles, enzymes become active and digests the compounds as required. Once digested, all building blocks (amino acids, lipids, etc.) are recycled

Mitochondria

Structure: Made from outer and inner membrane Fluid filled interior cavity called matrix Space within membrane celled inner membrane space Folds of inner membrane called cristae Mitochondria carry a separate small (37 genes) genome encoding mitochondrial specific products Function: Produce ATP (so more energy required the more mitochondria

Cytoskeleton

Structure: Composed of types of fibres or filaments (from smallest to largest): Microfilaments Intermediate filaments Microtubules Functions: Help to maintain the size, shape and integrity of the cell: Act as scaffolding across the cell Involved in intracellular transportation and cell movement

Microfilaments

Structure: Diameter: ~7 nm Comprised of actin molecules assembled in two long chains, twisted around each other Assembled and disassembled as required – they are dynamic Found around the periphery and lining the interior of cell Function: Bear tension and weight by anchoring cytoskeleton to plasma membrane proteins, and promote amoeboid motility (movement) if required (eg. macrophage) Important for shape of microvilli and cell

Intermediate filaments

Strucure: Diameter: 8-12 nm. Comprised of diverse range of different materials; one example: keratin Found (more distributed) in the cytoplasm of the cell. Usually the most permanent of cytoskeletal structures – they are less dynamic Function: Bear tension and weight throughout cell, e.g., during cell anchoring, Act as scaffold (kind of like what the organelles lean on and to be held up by) for cellular organelles, e.g., the nucleus.

Microtubules

Structure: (biggest) Tubular structure with a diameter of 25 nm - with central lumen of 15 nm diameter Comprised of tubulin dimers (alpha and beta), coiled, to form a tube Extends from centriole (an organising system within the centrosome) into cytoplasm/nucleus Assembled and disassembled as required - are dynamic Functions: Support cell shape and size Guide for movement of organelles, e.g., vesicles from Golgi to membrane - motor proteins walk along it while carrying vesicles Chromosome organisation (the chromosomes will segregate along microtubules) – really important for cell division Support and movement of cilia/flagella

Name the functions of plasma membrane proteins

Transport, Enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attacthment ot he cytoskelton and ECM

Describe transport

For example, channels, transporters (ions, molecules can pass through), may be general or selective, gated or not

Describe enzymatic activity

Substrate enters specific active site, carry out chemical reaction, may or may not be a part of a team of enzymes

Describe signal transduction

External signalling molecule causing communication of information to the inside of the cell

Describe cell-cell recognition

Use of glycoproteins (carbohydrate sugar + protein) as molecular signatures of the extracellular side of the cell Important for tissue typing - seeing if organ donor compatible

Intercellular joining

For example, gap junctions, tight junctions

Attachment to the cytoskeleton and extracellular matrix

For example, fibronectin mediates contact between cell surface integrins and ECM can facilitate movement of various things

What does amphipathic mean?

Partially hydrophilic/polar, partially hydrophobic/non-polar (relevant for proteins - as parts that are in the fatty regions are hydrophobic while those that are near the outside are hydrophilic)

Why is it so important we protect DNA

DNA doesn't change for each cell - you can't replace the cells DNA

Nucleolus:

Make RNA and assemble ribosomes