Unit 1
Cells
● Cells are the basic unit of life; small, membrane-bound structures with organelles
inside
Cell membrane
● Has a phospholipid bilayer
● Holds the cell together, and is selectively
permeable to control what enters and
leaves the cell (exchange)
● About 10nm in diameter
Cytoplasm
● Contains a liquid called cytosol, where organelles are suspended in (except for the
nucleus in eukaryotes)
Energy making
● Cells need a constant energy supply to carry out vital processes such as: protein
synthesis, DNA replication, cell division…
● This energy originally comes from fuel molecules such as glucose, consumed by
other organisms. These are broken down during aerobic or anaerobic respiration,
and the energy is released to produce Adenosine Triphosphate (ATP).
● ATP is a small and soluble molecule that provides a short-term storage of chemical
energy that cells can use to do work.
● This ATP then diffuses through the cell and breaks down into Adenosine
Diphosphate (ADP), by a process called hydrolysis, which breaks the
phosphoanhydride bond
Nucleus
● Present in all eukaryotes, the nucleus is
relatively large and separated from the
cytoplasm by a double membrane called the
nuclear envelope; which has many pores.
● Nuclear pores are important channels for
allowing mRNA and ribosomes to travel out,
as well as allowing enzymes such as DNA
polymerases and signalling molecules in
● It also contains chromatin, the genetic
material chromosomes are made of
● The nucleus also has darkly stained regions, called nucleolus, which are the sites of
ribosome production.
Rough Endoplasmic Reticulum (RER)
● Its surface is covered in ribosomes
● Formed from continuous folds of membrane continuous with the nuclear envelope
● Processes proteins made by the ribosomes
, Smooth Endoplasmic Reticulum (ER)
● Does not have ribosomes on
its surface, so it has a different
function to the RER
● Involved in the production,
processing and storage of lipids,
carbohydrates and steroids
Mitochondria
● Site of anaerobic respiration; are just
visible under light microscopes
● Surrounded by a double membrane,
with its inner membrane folded into
cristae
● The matrix liquid formed by the
cristae contains enzymes that produce ATP
● Small circular pieces of mitochondrial DNA
and ribosomes are also found in the matrix
for replication
Ribosomes
Ribosomal RNA is transcribed in the nucleus, and
folds up into subunits to make ribosomes
● Found freely in cytoplasm or in RER
● 80S (60S & 40S subunits): Eukaryotes
● 70S (50S & 30S subunits): Prokaryotes
● Site of translations (protein synthesis)
● Transcription: a molecule of mRNA, which codes for a protein, is created from a DNA
template
● Translation: most ribosomes attach to the RER, where they translate mRNA into
proteins, which are then transported by sacs from the ER
Golgi apparatus
● Modifies and packages proteins into transport
vesicles or lysosomes
● Vesicles: transport proteins elsewhere in the cell,
or ejected by exocytosis
● Lysosomes: contain enzymes that break old
organelles and bacteria
Cells
● Cells are the basic unit of life; small, membrane-bound structures with organelles
inside
Cell membrane
● Has a phospholipid bilayer
● Holds the cell together, and is selectively
permeable to control what enters and
leaves the cell (exchange)
● About 10nm in diameter
Cytoplasm
● Contains a liquid called cytosol, where organelles are suspended in (except for the
nucleus in eukaryotes)
Energy making
● Cells need a constant energy supply to carry out vital processes such as: protein
synthesis, DNA replication, cell division…
● This energy originally comes from fuel molecules such as glucose, consumed by
other organisms. These are broken down during aerobic or anaerobic respiration,
and the energy is released to produce Adenosine Triphosphate (ATP).
● ATP is a small and soluble molecule that provides a short-term storage of chemical
energy that cells can use to do work.
● This ATP then diffuses through the cell and breaks down into Adenosine
Diphosphate (ADP), by a process called hydrolysis, which breaks the
phosphoanhydride bond
Nucleus
● Present in all eukaryotes, the nucleus is
relatively large and separated from the
cytoplasm by a double membrane called the
nuclear envelope; which has many pores.
● Nuclear pores are important channels for
allowing mRNA and ribosomes to travel out,
as well as allowing enzymes such as DNA
polymerases and signalling molecules in
● It also contains chromatin, the genetic
material chromosomes are made of
● The nucleus also has darkly stained regions, called nucleolus, which are the sites of
ribosome production.
Rough Endoplasmic Reticulum (RER)
● Its surface is covered in ribosomes
● Formed from continuous folds of membrane continuous with the nuclear envelope
● Processes proteins made by the ribosomes
, Smooth Endoplasmic Reticulum (ER)
● Does not have ribosomes on
its surface, so it has a different
function to the RER
● Involved in the production,
processing and storage of lipids,
carbohydrates and steroids
Mitochondria
● Site of anaerobic respiration; are just
visible under light microscopes
● Surrounded by a double membrane,
with its inner membrane folded into
cristae
● The matrix liquid formed by the
cristae contains enzymes that produce ATP
● Small circular pieces of mitochondrial DNA
and ribosomes are also found in the matrix
for replication
Ribosomes
Ribosomal RNA is transcribed in the nucleus, and
folds up into subunits to make ribosomes
● Found freely in cytoplasm or in RER
● 80S (60S & 40S subunits): Eukaryotes
● 70S (50S & 30S subunits): Prokaryotes
● Site of translations (protein synthesis)
● Transcription: a molecule of mRNA, which codes for a protein, is created from a DNA
template
● Translation: most ribosomes attach to the RER, where they translate mRNA into
proteins, which are then transported by sacs from the ER
Golgi apparatus
● Modifies and packages proteins into transport
vesicles or lysosomes
● Vesicles: transport proteins elsewhere in the cell,
or ejected by exocytosis
● Lysosomes: contain enzymes that break old
organelles and bacteria
