cells are the basic unit of
any living organism.

Prokaryotic cells are only found in bacteria,
everything else has Eukaryote cells

• No Nucleus
• DNA is 'free floating'
• No membrane bound organells

• has a true Nucleus ( = enclosed in a membrane)
• has a variety of membrane bound organelles
• more complex cells

• Cell structure
• type of organelles
• numbers of organelles

Animals, Plants, Protozoa & Fungi
all have Eukaryote cells

Examples of different
types of cells:

• muscle cells
• palisade leaf cells
• nerve cells
• root cells
• fat cells

organelle numbers in the cells depend
on the cells job / function and how
quantity / energy demanding they are

All living things are made up of cells
(so cells are the building blocks of life)

• using cells plants, animals, etc. can build
  specialized structures (e.g. tissues or organs) ,
  for a variety of purposes
  (this is what gives us the diversity of living things)

They have their hereditary information
in one large (long) molecule of DNA

• they have only one chromosome

They have their hereditary information
stored in multiple chromosomes surrounded by
a Nuclear envelope made up of two membranes

• it is stored in the nucleus, in multiple chromosomes

For any chemical reaction, molecules must collide & collide with sufficient energy (activation energy), and correct orientation, so that the chemical bonds can change and a reaction occur

• enzymes can hep ensure correct orientation,
  by correcting the position of molecules
  ...as well as decreasing the amount of activation energy required

Activation energy = the amount of energy a reaction must overcome in order to occur

• enzymes lower the activation energy by destabilizing bonds in the substance they are more reactive

= Makes larger molecules out of smaller molecules
( - By joining things together)

= Breaks down large molecules into smaller pieces
( - By separating substances)

• Amino acids are joined together with peptide bonds
  forming a polypeptide chain

Depending on the different sequence of Amino Acids,
this determines the different enzymes
... hence determines the specific shape the enzyme folds into

• the shape of an Enzyme = determines its function

Certain Amino acids within the polypeptide chain will
interact with each other & can form either ...

- Hydrogen bonds
- Di-sulfide bridges

These two kinds of bonds are between sections of the enzyme and hold it together in the specific shape
... this is what gives the enzyme its 3D structure

• The most important part of an enzymes structure

= The area on the enzyme where the chemicals
involved in the reaction, bind together

• The shape of an Active site is very specific
  ... it corresponds of the shape of the substrate
  that bonds to it
  
  

substrates = the chemicals that bond to the enzymes active site (what is actually reacting)

• An Enzyme can only catalyses one kind of reaction
  ... they are highly specific because of the unique shape of the active site

= prevent enzymes from catalyzing reactions
(they 'stop' reactions)

= Compete with a substance to bind to the active site

... this means that if they win, the substrate can't bind
to the active site as the inhibitor is already there

• They tend to be irreversible and are therefore poisons

= Bind to a different part of the enzyme (not the active site)

... this alters the shape of the Enzyme and its Active site
... therefore binding of the substrate to the active site
is no longer possible

• this can be used by cells as a way of controlling rate of reaction

Each cell needs its own copy of DNA,
...so DNA needs to be able to make copies of itself
= Self replication

Replication has a series of steps all controlled
by enzymes & all requiring energy from ATP

1 - Double helix unwinds

2 - the weak hydrogen bonds are broken
by the enzyme 'helicase' (unzipping)

3 - New pre-made nucleotides assemble opposite each strand
& use energy (ATP) to join together,
using the enzyme 'polymerase'

4 - Two identical DNA molecules are formed
& they rewind into the twisted double helix

• The Complementary base pairing mechanism
  is how DNA replicates (C-G) (T-A)

• There are 2 identical DNA molecules made, but...
  ...each half of the original DNA strand gets a new copy of itself
  ... so each of the 2 cells will end up with a double helix, where one strand is new and one strand is the original
  
  
  

• This is done as it is quicker and safer as it is
  less likely to make a mistake

Many sections are copied at once because it is faster

• leading strand = copied directly along the whole strand
• lagging strand = copied in sections & then joined

• While chromosomes are long unraveling threads,
  they condense into smaller shapes for mitosis

I = Interphase
=chromosomes replicate to form 2 sister chromatids
held together by a centromere

(this isn't technically part of mitosis,
but another part of cell cycle)

P = Prophase

• The Chromatids shorten & thicken
• Nuclear membrane disappears
• Spindle fibers develop

M = Metaphase
= spindle fibers help Christmastides line up at the equator

A = Anaphase = Centromer split & individual chromatides **move towards 'poles**' pulled by spindle fibers

T = Telophase = At the poles, new nuclear membranes form around each group of chromatidss and
the plasma membrane begins to constrict

The cell...

• Performs its function (job)
• Rows in size
• makes what it will need for DNA replication

• the cell copies DNA, chromosomes are duplicated
  (DNA replication)

• Cells spend **90% of their
  time in the Interphase**

The cell....

• Grows more in size
• Performs its function (job)
• Makes what it needs for mitosis

• Makes new duplicated cells for
  growth & repair & replacement

• The previously duplicated DNA devides into 2 new cells
  & then the cytoplasm devides (Cytokineses)

• Cell division is most rapid during growth,
  not everyday life

• cells also replace themselves when they are worn out
• different cell types divide at different rates
  depending on how easily they were out

= Cell division into 2 identical daughter cells

• Every cell needs its own complete copy of DNA
  (witch are formed during the synthesis phase)
• For growth, repair & reconstruction of old or worn out cells

• It is a large molecule
• In the form of chromosomes it carries the 'genetic code' (information to make everything happen)

It is arranged in a twisted double helix
(has 2 connected strands twisted together)

• The 2 sides are strongly bonded together
• Made of alternating sugar & phosphate groups
• The 2 strands of DNA run anti-parallel (upside down)
  to each other

Adenine (A) --- Thymine (T) = 2 hydrogen bonds
Cytosine (C) --- Guanine (G) = 3 hydrogen bonds

• The bases are held together by weak hydrogen bonds
  (they only bond to the corresponding base
  due to their specific chemical structure)

• There are 2 chemical pathways that make up photosynthesis
  ... these 2 pathways** take raw materials (H2O & CO2)
  & rearrange them**
  ... then they join together to make Glucose
  (and a waste product of Oxygen)

Photosynthesis requires:

• Solar energy / light from the sun
• Chlorophyll
• Enzymes

Overall word equation:
Carbon Dioxide + Water = Glucose + Oxygen

= a light dependent reaction

• Happens in the Thylokoid membranes of Chloroplasts

Firstly:
Chlorophyll is a pigment that can absorb light (In the thylokoids)

• Electrons in the Chlorophyll are 'excited' by solar energy ... these high energy electrons are passed along a chain of molecules
  ... & the energy is used to make ATP
  ... the electrons are then returned to the Chlorophyll

Secondly:
Water is split into hydrogen & oxygen ...

• Oxygen is not needed so it is released as a gas
• Hydrogen is transferred by a carrier molecules
  into the 2nd pathway

= A light independent reaction

• Happens in the Stroma

• Hydrogen (from the 1st pathway), and CO2
  go into a complex biochemical cycle with lots of rearrangement
  ...until glucose forms as the final product

Glucose is used for:

• Respiration
• Stored as starch
• Used to make cellulose, fats & Amino Acids

All cells have a very thin
boundary between the cell and its environment

• this maintains the different concentrations
  of substances within the cell

• It is made of Phospholipids
  = A bi-layer (2 layers)

The phosphate heads = water loving = Hydrophilic
The Lipid tails = water hating = Hydrophobic

The membrane around the cells ...
= same kind of membrane around the organelles
(membrane bound organelles)

Cell membrane = Semi-permeable
= some things can get thorough and others can't
(only small non-charged things can get though,
big or charged things can't get through)

Requires energy
(as the particles are moving against
the concentration gradient)

• Needed for large molecules & charged molecules that are moving with the concentration gradient

• The process uses large Proteins that go right through the membrane as a pathways for the particle to travel
  
  

= these are called Chanel proteins or Carrier proteins
(& they are specific to molecules)

Definition:

The Random movement of particles,
resulting in a net Movement of a substance from an
area of high concentration to an area of low concentration, until the concentrations become the same (Equilibrium)

The difference in concentrations between 2 areas
= The Concentration Gradient

• Moving with the gradient = High to Low (Passive transport)
• Moving Against the gradient = Low to high (Active transport)
  
  

Moving from a high to low concentration gradient
= moving down the concentration gradient

Diffusion is faster if...

• The gradient (difference) is greater
• Smaller particles
• Higher temperature

• H2O, O2 & CO2; all diffuse freely across a membrane
  with a concentration gradient

• Osmosis is a special class of diffusion
  as it only diffuses water

= The movement of water across a semi-permeable membrane

From an area of high concentration to low concentration
(as with all passive transport)

Hypotonic = low Tonicity = few H2O particles = Dilute = High water potential / concentration

Hyertonic = high Tonicity = Lots of H2O particles = Concentrated = Low water potential / concentration
Isotonic = Same tonicity in and our of the cell

Exoocytosis = Adds to the cell membrane
Endocytosis = Uses up some cell membrane

Pinocytosis = 'cell drinking' = fluids
Phagocytosis = 'cell eating' = Solids

• ENERGY is needed
  (as in all active transport)

• The membrane is constantly being altered
  (added to or taken away from)...
  this is to allow 'things' in and out

= Specific carrier/transport proteins in the plasma membrane
that carries out active transport

• Harness the energy of ATP...
  to pump molecules / ions from low to high concentration

• Cells need to be small (volume) in order to diffuse substances both in & out of the cell

• When cells grow their volume increases at a
  faster rate than their surface area
  (cytoplasm / organals grow at a faster rate than the membrane)

Surface area = Squared (x2)
Volume = Cubed (X3)

When there is less membrane and more distance to
the center of the cell, the cells compensate by either;

• Dividing
• Being long
• being Bioconcave
• Having Villi

The greater the Surface Area to volume ration
= transport/ diffusion is more effective