Introduction to cells, the nucleus, the endomembrane system Flashcards
Week 9 and part of 10 (25 cards)
What are the three premises of cell theory?
All organisms are composed of one or more cells. Cells are the smallest living units of all living organisms. Cells arise only by division of a previously existing cell.
What is part of the reason why different organisms have such varying genome sizes? For example, why many plants have a very large genome, but the hummingbird’s is very small
Organisms who need to use more energy and have more complex functions require more space for these, therefore they are less likely to retain DNA sequences that are not essential.
What type of proteins are involved in the packing of DNA in eukaryotic cells?
Histone proteins
What is the structure of a nucleosome?
A collection of 8 histone proteins with two coils of DNA wrapped around it
As well as packing DNA, what else are histones involved in?
Allowing access to the DNA
Describe the structure of the nuclear envelope/membrane.
A double lipid bilayer membrane, with some liquid between the two layers
Describe the basic structure of nuclear pores
Large ring-shaped protein complexes which go through both membranes of the nuclear envelope
Where are ribosomes made in the nucleus?
In the nucleolus
What are the 5 main functions that occur in the nucleus?
Storage of DNA, ribosomal production, transcription of mRNA, replication of DNA, processing of mRNA
Do prokaryotic cells have an endomembrane system?
No
What is a signal sequence?
An extra chain of amino acid sequence in a protein that acts as a signal for localising that protein to its correct cell compartment
Do cytoplasmic proteins have signal sequences? Why/why not?
No, because they are already in the cytoplasm after translation
What are the two types of protein targeting/trafficking?
Post-translational translocation and co-translational translocation
Describe protein trafficking to non-endomembrane compartments, such as the nucleus, mitochondria or plastids. Include the name of this.
Post-translational translocation - the entire protein is translated in the cytoplasm and is then directed by the signal sequence to the appropriate compartment
Describe protein trafficking to endomembrane compartments, such as the golgi, plasma membrane or to be secreted.
Co-translational translocation - the ribosome starts as a free ribosome and begins to translate, until the signal sequence is recognised and the ribosome halts translation to move to the ER to become a bound ribosome to continue translation into the ER for further translocation.
What is the name of the ‘stacks’ of membrane in the endoplasmic reticulum or golgi apparatus?
Cisternae
What is the name of the liquid space in the endoplasmic reticulum?
Lumen
Why is the rough endoplasmic reticulum rough?
Because there are bound ribosomes from translating into the ER.
What are some main functions of the smooth endoplasmic reticulum?
Synthesis of lipids like steroids, metabolism of carbohydrates, detoxification of drugs and poisons, storage of calcium ions
What are some main functions of the rough endoplasmic reticulum?
Translation site for proteins destined to be secreted or for the plasma membrane, producing lipids and new membranes, sending proteins to the golgi, adding carbohydrates to proteins
Why do vesicles travel in a stop and go motion?
Because they are powered by ATP, they will halt when waiting for more power to travel
What do macrophages do?
White blood cells that remove pathogens by phagocytosis
What is the basic structure of a lysosome?
Small organelles with a single membrane that are like sacs of enzymes to break down molecules, including pathogens
What is exocytosis?
The export of material out of the cells via vesicles
