Cycle 1 - Light as Energy and Info Flashcards
Major features of chlamydomonas
- It is a green algae
- Single celled eukaryote
- Utilizes light
- For photosynthesis (energy)
- For detecting surroundings (via the eyespot) (information)
- Has a flagellum identical to humans
- It reproduces through binary fission
Features of the chlamydomonas life cycle
Why do organisms in stressful environments undergo sexual reproduction?
- It has two mating types + and - that are genetically distinct
- It begins at the gametes
- Notice that chlamy is haploid most of the time
- It naturally enters asexual reproduction: division by mitosis to produce clones
- If environmental conditions are harsh (ex., nutrient deprivation, not enough iron, nitrogen, etc.) it enters sexual selection
- Chlamy enters sexual reproduction during stressful conditions because it must adapt/mutate. Your babies need to be different to you in order to have an advantage or chance of survival.
- Chlamy is found as a zygote during the winter; a diploid cell
- It resists the coldness and survives for months or years without dividing
What is an ORF (open reading frame)?
Compare the number of ORFs/genome size for bacteria versus eukaryotes
ORF is a predicted value of how many genes actually code for protein and are not junk)
Generally, bacteria have more ORFs for their smaller genome size
- 1 for every 1,085 (bacterium); 1 for every 6,256 (chlamy, eukaryote); about the same for Arabidopsis (also eukaryote) 1 for every 4,924
Relationship between photosynthesis and possessing a chloroplast.
There is no chloroplast in the bacterium (no organelles), yet it is photosynthetic
In eukaryotes, photosynthesis requires a chloroplast
What percentage of chlamy proteins are found in Arabidopsis & humans, in just Arabidopsis, in just humans. What are their likely functions?
10% are found in just humans (flagella and cilia coding), 26% found in just Arabidopsis (chloroplast building, photosynthesis), and 33% are found in both (mitochondria, ancestral DNA, hexokinase, etc)
What characteristics does Chlamy have that makes it a “model system” for experimentation?
- It utilises light in two different ways
- Its flagella are developmentally identical to cilia in our epithelial lining
- It is haploid, so you can highlight and create mutants easily
- Its entire genome has been sequenced; we know a lot about its proteind
- Has genes found in eukaryotes and prokaryotes plus it has a chloroplast
Come up with a list of specific genes/processes that could be disrupted in cells that are unable to display phototaxis.
- Genes that code for channelrhodopsin
- Genes that code for carotenoids
- Genes that code for opsin
- Genes that code for enzymes involved in the synthesis of retinal
- Genes that control the protein movement in the flagella
- Photosynthesis
- Movement
Why do biological systems primarily absorb visible wavelengths of the electromagnetic spectrum?
Pigments can only absorb visible light because it is the only light where the photon energy matches the amount of energy needed to delocalize an electron in the conjugated system
Describe the basic organization and functional features of the eyespot.
- Orange/red = carotenoid layer, the reflector which helps orient chlamy depending on where light bounces off and hits channelrhodopsin
- Eyespot is at the edge of the chloroplast membrane, which is pressed against the plasma membrane (eyespot is sandwiched)
- Channelrhodopsin (blue) is a protein on the plasma membrane that functions in information reception for movement
State the structure and function of channelrhodopsin
- Channelrhodopsin is a light-gated channel found in chlamy
- It is a photoreceptor: a protein that has a pigment attached to it allowing it to absorb light.
- It has two parts, a pigment (retinal) and a protein (opsin). Only pigments can absorb light.
- When it absorbs light, it allows ions to flow into the membrane
State the mechanism of photoisomerization of retinal and its consequences (aka phototransduction)
- Retinal is photoisomerized by light, meaning that in the absence of light, it is trans (more stable), but energy from light attacks its double bond and makes it cis.
- Photons breaks the double bond. For a split second, it is a single bond that rotates 180 degrees, and then double bond reforms to make the new cis conformation
Describe the key similarities and differences between channelrhodopsin in the eyespot and rhodopsin in the human eye.
- Rhodopsin is not the ion-gated channel in our eyes, whereas channelrhodopsin is the ion-gated channel in chlamy
- Rhodopsin requires more signalling proteins
- Channelrhodopsin is a type 1 opsin and is homologous to a bacterial opsin, rhodopsin is a type 2 opsin (a common receptor in our body that is involved in functions like smell, hormone, etc.)
- Both are a 7 transmembrane protein, and bind to retinal
Define homology
The existence of shared ancestry
Outline the photochemistry of photosynthesis and phototransduction
- Photochemistry in photosynthesis:
- Oxidation of chlorophyll (photosystem event): Ch* → Ch+ and electron
- Photochemistry in phototransduction (eyespots, eyes)
- Isomerization of retinal (photochemical event): trans → cis → trans → etc.
State and rationalise the steps of Northern analysis
State the importance of the probe being “labelled” and single stranded.
- Extract mRNA
- Gel electrophoresis
- Used to separate the mRNA by size
- Place it in a salt solution with membrane on top → mRNA transfers to the membrane
- Used to read the data
- Add DNA probes (will bind to complementary sequence → hybridize)
- DNA probes: free nucleic acid units
- The probes are able to bind and make it visible under x-ray
- Needs to be complementary (to specific mRNA) and single stranded so it can bind to said specific mRNA
- Needs to be labelled, i.e. radioactive, so the x-ray can see it
