Eukaryotic meaning
meaning ‘true nucleus’, have membrane bound organelles
Prokaryotic meaning
meaning ‘no nucleus’, have no membrane bound organelles
Organelle
structure within a cell - the structure will relate to its function
Nucleus
- has a double membrane with pores in it
- contains chromosomes (made of DNA, contain genes that control synthesis of proteins) and a nucleolus
Nucleolus
- darker staining region within the nucleus –> is active so is darker
- dense body where ribosomes are made, makes rRNA and pre-ribosome particles
Ribosomes
- Made of rRNA and proteins
- Can be free in the cytoplasm or attached to the rER
- This is the site of protein synthesis
- In Eukaryotic cells they are 80S (in prokaryotes they’re 70S)
rough Endoplasmic Reticulum
- a system of interconnected membrane bound, flattened sacs
- ribosomes are attached to the outer surface
- Proteins are made on the ribosomes and then transported to other parts of the cell
Cell membrane
-phospholipid bilayer containing proteins and other molecules forming a partially permeable barrier
smooth Endoplasmic Reticulum
- system of interconnected membrane bound, flattened sacs but without ribosomes attached to the surface
- are involved in the synthesis of lipids and steroids
Mitochondrion (Mitochondria - plural)
- have a double membrane, with inner membrane foldings called cristae
- site of later stages of aerobic respiration (where ATP is produced)
- number found in cells depends on energy requirements of the cell
Centrioles
- hollow cylinders made up of a ring of 9 microtubules
- are needed for the formation of the spindle during cell division and in transport within the cytoplasm
- always come in pairs which are placed at 90° to each other
- not found in plant cells
Lysosomes
- spherical sacs containing digestive enzymes bound by a single membrane
- are used to breakdown unwanted substances in the cell and for the destruction of whole cells
Golgi Apparatus
- stacks of parallel, flattened, membrane bound sacs of decreasing size
- they’re formed by the fusion of vesicles from the endoplasmic reticulum
- modifies proteins and packages them into vesicles for transport
- vesicles arrive at the cis face and leave at the trans face
Features of a prokaryotic cell
- contains no nucleus
- no membrane bound organelles
- all unicellular
- have circular chromosomes not associated with histone proteins
- smaller 70S ribosomes
Processes cells need to do:
- make proteins/enzymes
- repair damage
- replicate
- respiration
- storage
- transport
Cells are dynamic
nothing is static; there is continual movement and change
Mitosis
- 2 body cells created
- 46 chromosomes in daughter cells
- 1 division
- not identical to the parent cell
Meiosis
- 4 gametes created
- 23 chromosomes in daughter cells
- 2 divisions
- gives rise to variation
How does genetic variation occur?
Due to random assortment and crossing over. Could also be due to random fertilisation and mutations.
Independent Assortment
Wen the chromosomes pair up with their homologous pair. The way the sister chromatids line up can be different and the DIFFERENT COMBINATIONS OF ALLELES produced creates variation. Variation is caused due to the random alignments of the homologous chromosomes in the first division
Crossing Over
Creates variation by producing chromosomes that contain different combinations of alleles from both parents (molecular scissors). Makes chromosomes that neither parent made; essentially cut and stick
What is the point of intersection between 2 chromosomes in crossing over called?
Chiasma (chiasmata)
Sex Linkage
gene on the X chromosome (males are more likely to have it than females –> they have 2 alleles so have a greater chance of getting a dominant allele to cancel out recessive allele)
Linkage groups
inherit alleles on the same chromosome
