Topic 3 Flashcards
Nucleus:
-surrounded by a double membrane called the envelope, which contains pores enabling molecules to enter and leave the nucleus.
-the nucleus contains DNA wrapped around histone proteins in a complex called chromatin and a nucleolus which is the site of ribosome production.
Rough endoplasmic reticulum:
- a series of flattened sacs enclosed by a membrane with ribosomes on the surface. The RER folds and processes proteins made on the ribosomes; often located close to the nucleus.
Smooth Endoplasmic reticulum:
a system of membrane bound sacs that produces and processes lipids and steroids.
Golgi Apparatus:
A series of fluid-filled, flattened and curved sacs with vesicles surrounding the edges. The golgi apparatus modifies and packages proteins (after the RER) as well as lipids. (e.g. is glycosiliates proteins or concentrates proteins) It also produces lysosomes.
Mitochondria:
usually oval shapes and bound by a double membrane called the envelope. The inner membrane is folded to form projections called cristae, with a fluid matrix on the inside containing the enzymes needed for cellular respiration.
Centrioles:
Hollow cylinders containing a ring of microtubules arranges at right angles to eachother. Centrioles are involved in cell division.
Ribosomes
- in eukaryotic cells there are 80s ribosomes (in prokaryotic cells they are 70s). They are composed of two subuntis. The site of protein synthesis.
Lysosomes:
-vesicles containing digestive enzymes, bound by a single membrane
Protein trafficking:
- Proteins are produced on the ribosomes
- Proteins which are produced on the ribosomes on the surface of the RER are folded and processed in the RER
- The proteins are then transported from the RER ti the golgi apparatus in vesicles (involves the fusion of membranes)
- They are then modified (e.g. glycosiliation-carbohydrates are added to form a glycoprotein) in the golgi appartus
- The golgi appartus packages the proteins into vesicles to be transported around the the cells to where they are required. Some proteins such as extracellular enzymes leave the cell by exocytosis. (the vesicle membrane fuses with the cell surface membrane to release the contents)
free ribosomes if they are intracellular, rer if they are extracellular
Structure and organelles of prokaryotic cells:
Cell wall- the cells rigid outer covering made of peptidoglycan. Provides structure and support of the cell
Slime Capsule- protective slimy layer which prevents dehydration of the cell and enables adhesion to surfaces
Plasmid- circular pieces of DNA
Flagellum- a tail-like structure which rotates to move the cell (can also be in eukaryotic e.g. sperm cell)
Pilli- hair like structures which attach to other bacterial cells (allowing the exchange of plasmids)
70s ribosomes- composed of two subunits and site of protein synthesis
Mesosomes- infoldings of the inner membrane- their function is debated- believed by some scientists that they contain enzymes required for respiration.
Features of the ovum:
- Contains the zona pellucida- a protective coating which the sperm have tp penetrate in order for fertilisation to occur, it then hardens after they have entered.
- Contains a haploid nucleus so that a full set of chromosomes is restored at fertilisation.
- Follicle cells form a protective coating around the egg.
Features of the spermatozoa:
- sperm cells contain many mitochondria to provide enrgy for the rotation of the flagellum which enables the cell to move
- acrosomes contain digestive enzymes which break down the zona pellucida and allow sperm to penetrate the egg.
The process of Mammalian Fertilisation:
- Acrosome reaction- Enzymes digest the follicle cells and zona pellucida. The membrane of the acrosome fuses with the sperm cell membrane- digestive enzyme, acrosin, released by exocytosis.
- Sperm bind to specific receptors on egg cell surface membrane and membrane fuses
- Cortical reaction- corticle granules and lysosomes move to egg cell surface membrane, fuse and release contents (granules) by exocytosis. This causes the egg surface membrane and zona pellucide to harden to prevent polyspermy. The new, hardened membrane is called the fertilisation membrane.
- there is a constant movement of ions trhough channels (more positive inside the egg cell) - Egg and sperm haploid (gamete) nuclei fuse together forming a diploid zygote.
- there are mitochondria within each gamete cell which release ATP energy for reactions within the cell.
- there are lipid droplets which provide energy for growth and development.
What is a locus?
the location of genes on a chromosome
What is autosomal linkage?
- alleles on the same chromosome are said to be autosomally linmked and are inherited (as if they were the same gene)
- the closer the loci of the genes on the chromosome, the more closely lonked they are. This is because they are far less likely to be separated during recombination in meiosis.
What is sex-linkage?
They occur on the X chromosome. Some genetic disorders are sex-linked and therefore are much more common in men because men only need one allele to be expressed (X,Y) vs women need the allele on both X chromosomes to be expressed (X,X)
e.g. Haemophilia (absence of clotting factor so blood doesn’t clot properly) or red-green colourblindness
The three stages of the cell-cycle:
- mitosis- prophase, metaphase, anaphas and telophase
- cytokinesis- during this stage, the cytoplasm divides, thus producing two daughter cells
- interphase (involving three seperate stages)
The three stages of interphase:
G1- during this stage, the cell grows (cell enlargement- more cytoplasm, protein synthesis)
S- chromosomes are replicated (DNA replicates) and begin to condense to form chromatin
G2- the cell prepares to divide (proof-reading enzymes check if DNA has been copied correctly), replicating organelles for a full set in each new cell