Basic components of living systems: Eukaryotic cell structure Flashcards
What is a eukaryotic cell?
multicellular and make up animal, plant and fungi
What do chemical reactions require?
enzymes and specific reaction conditions
what is metabolism?
involves the synthesis and breaking down of molecules
membrane bound organelles provide…
distinct environments and therefore conditions for different cellular reactions are not the same
What is DNA’s function?
directs the synthesis of all proteins. In this way DNA controls the metabolic activities of the cell as many of these proteins are necessary enzymes for metabolism to take place.
The nuclear envelope
double membrane to protect it from damage in the cytoplasm. Contains nuclear pores. DNA is too large to leave the nucleus, therefore it it is transcribed into smaller mRNA molecules.
Histones and chromatin
DNA associates with proteins called histones to form a complex called chromatin. Chromatin coils and condenses to form chromosomes which are only visible when the cells are prepared to divide.
Nucleolus
-responsible for producing ribosomes
-composed of proteins and RNA.
-RNA is used to produce ribosomal RNA (rRNA) which is then combined with proteins to form ribosomes
Mitochondria function
-site of cellular respiration
-produces ATP which is the carrier of energy
Mitochondria structure
-double membrane
-inner membrane is highly folded to form structures called cristae
-the fluid is called the matrix
-the membrane forming cristae contains enzymes for aerobic respiration.
-contains its own DNA called mitochondrial (mt) DNA. Therefore it can produce their own enzymes and reproduce itself. Mitochondria was engulfed.
Vesicles
membranous sacs that have storage and transport roles. They contain fluid and its function is to transport materials inside the cell.
Lysosomes
-specialised form of vesicle
-contains hydrolytic enzymes which are responsible for breaking down waste in cells, including old organelles. They breakdown pathogens ingested by phagocytic cells.
Cytoskeleton
network of fibres necessary for the shape, stability and movement. The three components are microfilaments, microtubules and intermediate fibres
microfilaments
-formed from actin protein
responsible for cell movement and contraction during cytokinesis ( the process when the cytoplasm is divided)
microtubules
-formed from tubular protein
- tubes that act as tracks for the movement of organelles
-determines shape of cell
-spindle fibres which have a role in the physical segregation of chromosomes in cell division are composed of microtubules
intermediate fibres
provides mechanical strength to cell
centrioles
-composed of microtubules
-two associated centriols form a centrosome which is involved in the organisation of spindle fibres during cell division
flagella function?
-enable cell motility
-longer than cilia
-sometimes used as a sensory organelle detecting chemical changes
cilia function?
-present in great numbers
-stationary cilia are present in sensory organs
-mobile cilia beat in a rhythmic manner creating current and causes fluid or objects to move, e.g they remove mucus from the lungs in the trachea.
structure of flagella and cilia
A circle of 9 groups of microtubules, every group has two microtubules. The centre has two microtubules. This is called the 9+2 arrangement. Pairs of microtubules slide over each other causing movement.
The endoplasmic reticulum
network of membranes enclosing flattened sacs called cristernae. There is the smooth ER and the rough ER
smooth endoplasmic reticulum
responsible for lipid and carbohydrate synthesis and storage
rough endoplasmic reticulum
-ribosomes are bound to the surface
-responsible for the synthesis and transport of proteins
why do secretory cells have more endoplasmic reticulum?
Because they release hormones and enzymes which are proteins
ribosomes
-free floating or attached to endoplasmic reticulum
-not surrounded by membrane
-made from rRNA and protein molecules
-site of protein synthesis
-mitochondria, chloroplasts and prokaryotic cells also contain ribosomes
-translates genetic material into proteins
-contains two subunits which come together during protein synthesis, a smaller subunit 40S and larger 60S
Golgi apparatus
-compact structure formed of cisternae and doesn’t contain ribosomes
-modifies proteins and packages them into vesicles
what occurs after proteins are synthesised in ribosomes on rough ER
1) synthesised on ribosomes bound to endoplasmic reticulum
2) passed into cisternae and packaged into transport vesicles
3)vesicles containing new proteins move towards the Golgi apparatus via the transport function of the cytoskeleton
4) vesicles fuse with cis face of Golgi apparatus and proteins enter. The proteins are structurally modified.
5)secretory vesicles carry proteins that are to be releases from the cell. vesicles move and fuse with cell surface membrane, releasing their contents by exocytosis.
what is the surface outer cell membrane made of?
2 layers of phospholipids (phospholipid bilayer)
Describe the structure of a phospholipid?
-hydrophilic phosphate head (water attracting)
-two hydrophobic fatty acid tails
-therefore in aqueous conditions, the hydrophilic heads form two outer rows while the hydrophobic tails are protected in a non-aqueous core.
- this creates a partially permeable membrane.
-fluid but stable
how do vesicles move along the cytoskeleton?
by motor proteins
what is the role of the nucleus?
DNA synthesis, directs protein synthesis
Describe the structure of the rough endoplasmic reticulum? (3 marks)
-ribosomes found on the surface
-phospholipid bilayer
-contains cristernae
-continuous nuclear envelope
explain the role of the membrane in the rough endoplasmic reticulum? (2 marks)
-proteins are packaged into vesicles
-compartmentalisation
-hold ribosomes in place
Describe the structure of the rough endoplasmic reticulum?(3 marks)
-ribosomes attached to the surface
-cisternae structure
-phospholipid bilayer
explain the role of the membrane in the rough endoplasmic recticulum?(2 marks)
-holds ribosomes at surface where translation occurs
-membrane allows compartmentalisation
-separates synthesised proteins from cytoplasm
