Building Life: the evolution of complex cells

Question 1

nucleus

Answer 1

membrane bound space that contains genetic material. Absence or presence defines prokaryotes and eukaryotes.

Question 2

prokaryotes - subsets, features, DNA, organisation

Answer 2

Bacteria and archaeans
No nucleus
Most do not synthesis sterols and have hopanoids instead
Archaeans are much more similar to eukaryotes than bacteria - share many genes involved in transcription and translation and DNA is packaged in histones as well

Nucleoid: discrete region of the cell interior where DNA is concentrated

Bacteria often have plasmids as well - involved in horizontal gene transfer and have a genes. Often cause antibiotic resistance
Lack extensive internal organisation
Smaller with high surface area to volume ratio.

Question 3

eukaryotes - subsets, DNA, size

Answer 3

Animals, plants, fungi and protists
Nucleus - allows for translation and transcription to be separated in space and time (more complex regulation of gene expression)
Might have cholesterol in their membranes (a type of sterol)
Often complex and organised
Larger

Question 4

organelles

Answer 4

defined compartments with a membrane. They have specialised functions.

Question 5

ER

Answer 5

Endoplasmic reticulum: synthesises proteins and lipids.

Question 6

Golgi

Answer 6

Golgi apparatus: modifies proteins and lipids made by the ER and sorts them for transport.

Question 7

lysosomes

Answer 7

Lysosomes: contain enzymes and break down macromolecules.

Question 8

peroxisomes

Answer 8

Peroxisomes: contain enzymes that are involved in metabolic reactions such as synthesising phospholipids.

Question 9

mitochondria

Answer 9

Mitochondria: harness energy for the cell.

Question 10

cytoskeleton

Answer 10

Cytoskeleton: a protein scaffold that helps the cell maintain shape and serves as tracks for the movement of substances.

Question 11

chloroplasts

Answer 11

Chloroplasts: convert energy of the sun into chemical energy in plants.

Question 12

cytoplasm

Answer 12

Cytoplasm: the entire contents of the cell.

Question 13

cytosol

Answer 13

Cytosol: jelly-like substance that surrounds the organelles.

Question 14

evolution from prokaryotes to eukaryotes

Answer 14

Archaea ancestor
Archaea engulfed a bacteria and a symbiotic relationship was formed
archaeal cell provides nutrients and bacteria provides ATP
Codependence evolved - took millions of years (endosymbiosis)
Many genes in the bacterial were transferred to the host cell nucleus so that the mitochondrial genome only has dozens of genes
Mitochondria also has cristae now that increase surface area for ATP production
Two layers of mitochondria cell - one formed in the engulfing and it is comprised of phospholipids like a eukaryotic membrane. Inner membrane is more prokaryotic
Mitochondria DNA is circular not like eukaryotic and the genes are more similar to prokaryotic genes
Timing and order of formation of organelles is not know
Last eukaryotic common ancestor (LECA) - eukaryotic cell that contained all the features common to eukaryotic cells
Cyanobacteria into cells formed chloroplasts

Question 15

the endomembrane system - eukaryotes? structure? definition? functions?

Answer 15

In eukaryotes, the surface area of the intracellular membrane is about 10x greater than that of the plasma membrane
Organelles are connected by membrane bridges or by vesicles (small, membrane enclosed sacs that transport substances within a cell or from the interior to the exterior).
Vesicles fuse to membranes, unloading contents

Endomembrane system: the continuous and interconnected membranes including the nuclear envelope, ER, Golgi apparatus, lysosomes, the plasma membrane and vesicles.

Usually continuous in plants through pores called plasmodesmata
Not common in prokaryotes (photosynthetic bacteria have internal membranes for harnessing light).
Creates two distinct worlds - inside the system and in the cytoplasm
Different environments in each compartment

Exocytosis: when a vesicle fuses with the plasma membrane and empties its content into the extracellular space.

Endocytosis: a vesicle buds off the plasma membrane, encloses material and brings it to the interior.

Question 16

the nucleus as part of the end-membrane

- nuclear pores and envelope, ribosomes

Answer 16

Innermost organelle of the endomembrane
Stores DNA which encodes information for the activities and structures of the cell

Nuclear envelope: defines the boundary of the nucleus. Consists of two membranes which each have a lipid bilayer with associated proteins.

Nuclear pores: openings between the two membranes. Large protein complexes that allow molecules to move into and out of the nucleus.
Important for communication eg. Transcription factors
mRNA moves through these pores and bind to free ribosomes

Ribosomes: site of protein synthesis in which amino acids are assembled into polypeptides.

Question 17

endoplasmic reticulum as part of the endomembrane

Answer 17

Continuous with nuclear envelope
Bound by a single membrane
Can make up half of the total membrane
Produces and transports lipids and proteins
Interconnected tubules and flattened sacs

Lumen: continuous interior of the ER

Rough endoplasmic reticulum: studded with ribosomes and it synthesises transmembrane proteins, proteins for use in the cell and proteins for secretion.

Smooth endoplasmic reticulum: lacks ribosomes and is the site of fatty acid and phospholipid biosynthesis.

Question 18

Golgi as part of the endomembrane

Answer 18

Proteins and lipids from the ER move to it by vesicles (within the vesicle or in its membrane)
Part of a biosynthetic pathway involved in sequentially modifying and delivering proteins and lipids

Cisternae: flattened membrane sacs

Cisternae surrounded by vesicles (transport between cisternae and around and out of cell)
Enzymes in the Golgi modify proteins and lipids - sequential because different enzymes in different areas
Glycoproteins and glycolipids are formed - involved in detection and reception
Glycoproteins - form a flexible and protective coating over the plasma membrane
Some vesicles move from the Golgi to the ER - retrieve proteins that were accidentally moved forward and to recycle membrane components

Question 19

three roles of Golgi

Answer 19

Modified proteins and lipids
Acts as a sorting station
Synthesises most of the cell’s carbohydrates

Question 20

lysosomes as part of the endomembrane

Answer 20

Lysosomes: specialised vesicles derived from the Golgi that degrade damaged or unneeded macromolecules.

Contain a variety of enzymes
Golgi packs things for degradation into vesicles which fuse with lysosomes, delivering their contents into the lysosome
Enzymes are synthesised in the RER, sorted in the Golgi apparatus and packed into lysosomes
Golgi sorts and delivers specialised proteins to imbed into the lysosome membrane such as proton pumps that maintain a pH of about 5
Transport proteins move the broken down products into the cytosol for use by the cell
Enzymes in the lysosomes would not survive in the cell pH 7 so this is important

Question 21

how did the last eukaryotic ancestor become a photosynthetic cell?

• phagocytosis

Answer 21

Endosymbiosis of a cyanobacterium
Beneficial relationship

Phagocytosis: cell ingesting another cell (can be a other things or parts of cells too). Subtype of endocytosis.

Two membranes form (plasma membrane of eukaryote and bacterial cell)

Question 22

evidence for endosymbiosis

Answer 22

Double membrane
Ribosome - differences between eukaryotic and prokaryotic ribosomes
DNA

Question 23

what distinguishes the mitochondrial membrane from the endomembrane system?

Answer 23

Inner membrane would be more similar to a prokaryote and the outer membrane would be more similar to a eukaryote
Protein differences, types of lipids, cholesterol in a eukaryotic membrane

Question 24

what about the chloroplast DNA could help determine what type of organism ingested?

Answer 24

Organelle has DNA - not usual in the endomembrane system
Circular chromosomes compared to linear chromosomes of eukaryotes
DNA sequence for circular chromosomes and analyse them - would match up to prokaryotes, especially the cyanobacteria

Question 25

mitochondria and evolution

Answer 25

DNA rapidly replicates
Have their own genome
Still have some independence - mutation arises and they may begin to compete, don’t cooperate (rebel like in cancer)

Question 26

surface area and eukaryotes

Answer 26

Eukaryotes overcome surface area problem with endomembrane system
Can compartmentalise and carry out specialised functions in different areas
Lysosome - important to compartmentalise so that the cell does not have enzymes (toxic) floating around and also helps with pH issues. If a lysosome breaks open, pH differences may make the bad enzymes not be that harmful to the cell

Question 27

using GFP to study organelles

Answer 27

Engineer cells to have GFP attached to proteins
GFP can be used to visualise the position of the functional protein in a cell
Put gene with a gene of protein of interest
Fuse them and the functional protein - protein will drag the GFP along
Signal sequence -
Incomplete piece of a protein -
Can see where the proteins go and may see that there is a circle and that would be the plasma membrane

Question 28

where is GFP from?

Answer 28

protein from jelly fish