Cell Structure & Diversity 4 - Photosynthesis & The nucleus Flashcards
What is the equation for photosynthesis?
6CO2 + 6H2O»_space;»>plant»»>light»»> C6H12O6 + 6O2
What are chloroplasts?
The organelle where photosynthesis occurs
What are chloroplasts similar to?
Mitochondria
What is the structure of a chloroplast?
They have an outer and inner membrane which contains thylakoids. The thylakoid membrane encloses the thylakoid space and outside of the thylakoids is the stroma. Also contains DNA and ribosomes
Where does the light reaction take place?
The thylakoid membrane which has a large surface area
Where does carbon fixation occur?
In the stroma
What happens in the light reaction?
Light energy is captured and converted into chemical energy using pigment and protein complexes embedded in the thylakoid membrane.
What is the structure of the thylakoid membrane?
Lipid bilayer
What are photosystems?
protein complexes which contain chlorophyll
What is the function of chlorophyll?
To absorb light energy
What does light energy produce?
High energy electrons
What do high energy electrons do?
Travel through the photosynthetic electron transport chain
What photosystem do electrons first go to?
Photosystem 2
How do the electrons travel?
In pairs
Where are the electrons obtained from?
The splitting of water
What happens as a result of water splitting?
Oxygen is released as a byproduct
What happens at photosystem 1?
The electrons gain energy from light
Where is the second location electrons move to?
Cytochrome complex
What happens at the cytochrome complex?
Electrons lose energy which is then used to pump protons across the membrane into the thylakoid space
Where do electrons move after the cytochrome complex?
Photosystem 1
What happens at Photosystem 1?
More light energy is absorbed by the chlorophyll and transferred to the electrons to make high energy electrons which are held in NADPH carriers.
What does the cytochrome complex create?
The proton gradient in the thylakoid space so that chemiosmosis can occur through the ATP synthase to make ATP
What are the outputs of the photosynthetic electron transport chain?
ATP, NADPH and oxygen
What is ATP and NADPH used for?
The Calvin cycle only
What occurs during the Calvin cycle?
ATP and NADPH produced in the light reaction are used to fix CO2 and produce carbohydrate
Where does the Calvin cycle occur?
In the stroma of the chloroplasts
What occurs during fixation?
CO2 binds with a 5 carbon molecule to make 2 three carbon molecules which uses no energy
What occurs during reduction?
Low energy 3 carbon molecules are converted into high energy 3 carbon molecules which requires ATP and NADPH. The 3 carbon sugar leaves the cycle to form glucose
What happens during regeneration?
The 3 carbon molecules are converted back into 5 carbon molecules which can be used during fixation
What is the output the Calvin cycle?
A 3 carbon sugar which is converted into glucose. Glucose is then broken down during respiration in the mitochondria
How big is the nucleus?
5-10 micrometers making it the most prominent organelle in eukaryotic cells
How many nuclei are in a cell?
Most cells contain one but they can have more or even none
What is contained in the nucleus?
Most of the cells genes but some are also found in the mitochondria and chloroplasts
What is the function of the nucleus?
A place to hold inherited genetic information and Aldo the control centre of cells which makes sure the DNA isn’t damaged and by turning genes on and off it can control what the cell does
What is the nuclear envelope?
The structure which surrounds the nucleus
What is the structure of the nuclear envelope>
Double membrane which are both composed of phospholipid bilayers
What is the nuclear envelope continuous with?
The endoplasmic reticulum meaning that the space between the two layers is continuous with the lumen
What does the nuclear pore complex do?
Control the movement of molecules out of, or into the nucleus
What moves out of the nucleus through the nuclear pore complex?
mRNA, tRNA and ribosomal subunits
What is then function of mRNA?
Messenger RNA carries information from a gene
What is tRNA and ribosomal subunits needed for?
Building proteins
What moves into the nucleus through the nuclear pore complex?
control signals, building materials and energy
Why are control signals needed?
To know when to turn a gene on or off
What are building materials needed for?
RNA
What is energy needed for?
Chemical synthesis
What is found inside then nuclear envelope?
The nuclear membrane lines the inner surface of the nuclear membrane
What is the structure of the nuclear lamina?
Intermediate filaments (lamina) which form a network and anchor nuclear pores
What is the function of the nuclear lamina?
Maintains the shape of the nucleus and helps organise packing of DNA within the nucleus
What is the nucleolus?
A prominent nuclear structure within non-dividing cells
How many nucleoli are present in a nucleus?
May be one or more than one depending on the species and which stage of the cell cycle it is at
What is the function of the nucleolus?
Responsible for making ribosomal RNA which combines with proteins to produce ribosomes
What is a feature of structures within the nucleus?
They aren’t fixed, they change based on what the cell is doing
What is DNA?
A nucleotide polymer
How much DNA is in each human cell?
2.5 m which is 250,000 times the diameter of the nucleus
How must DNA be arranged in the nucleus?
Very well packed but also accessible to allow for transcription to occur
What is the diameter of DNA?
Around 2 nanometres
What does DNA do first to fit into the nucleus?
Interacts with specific proteins called histones (H2A, H2B, H3 and H4). Two of each kind (8 in total) cluster together and then DNA wraps around them
What is the cluster of histones called?
Nucleosome
What is the size of a nucleosome?
10nm in diameter
What happens after a nucleosome has formed?
DNA further interacts with another histone (H1) causing the 10nm fibre to form a 30nm fibre
What happens with 30nm fibres?
They are supercoiled tighter to form 300nm fibres
What happens with 300nm fibres?
They are coiled even more to form metaphase chromosomes during cell division
What is a karyotype?
How chromosomes are displayed which can be used to screen chromosomal defects
How is euchromatin shoes in images?
Light patches
What is the features of euchromatin?
It is less dense and contains genes which are currently being used by the cell
How is heterochromatin shown in images?
Dark patches
What is the features of heterochromatin?
It is more dense and contains genes which aren’t being used by the cell so leaves more space for genes which are being used by the cell
What is the relationship between euchromatin and heterochromatin?
Dynamic
What is the location of chromosomes within the nucleus during interphase?
Not random
What is the function of the nuclear lamina with relation to chromosomes?
Keeps them in position
What shows the location of each chromosome?
Coloured tags, pairs aren’t generally found together
What is a feature of cancer cells?
Their chromosomes are very disorganised
