Chapters 7, 8, & 9 HL Flashcards
What is the epidermis of plant?
outer layer that protects leaves & secretes wax to form a waterproof coating to the leaf (waxy cuticle) that prevents excessive transpiration
Function of lignin in plants.
found along xylem walls to prevent collapse / resists tension
Function of hyphae of fungus
hyphae of mutualistic fungus may enhance movement of selected ions into roots / increase SA
Adaptations of root hairs
- thin, long for efficient absorption + SA
- have large amounts of mitochondria to conduct cellular respiration & generate ATP for protein pumps
Adaptations of halophytes
- storing excess ions in vacuoles
- active transport of ions BACK into soil
- isolating ions in leaves + shedding them
- increasing uptake of non-harmful ions e.g. K+ to increase osmosis
- excretion of ions from special glands
Define xylem
long tubular structures w/ strong side walls which transport water & minerals
How does sucrose move through phloem?
- moves by apoplastic & symplastic routes
- moves through plasmodesmata (during unloading of sucrose from companion cells)
Distinguish b/w apoplastic & symplastic pathways
APOPLAST: materials pumped across CELL WALL by membrane proteins
SYMPLAST: materials can pass into sieve tube via interconnecting plasmodesmata (through CYTOPLASM)
Define plasmodesmata.
narrow cytoplasmic connections w/ adjacent companion cells
Example of source
leaves
Example of sink
roots, fruits, seeds
Function of companion cell
- lies adjacent to sieve tube cells
- provides metabolic machinery for sieve tube cell
Sieve plats
have wide opening to ease movement of cytoplasm b/w cells
rigid walls of sieve tube cells
- allows for build-up of hydrostatic pressure
cell membrane on inside of sieve tube cell walls
- holds sap inside sieve tubes
- has pumps to load / unload sucrose
lumen of sieve tube
has no organelles that would obstruct the flow of sap
What provides primary growth / lengthening of plant
apical meristems
What provides secondary growth / widening of plant
lateral meristems
Outline the functions of auxin
- produced by tip of stem / shoot tip
- responsible for cell elongation
- changes patterns of gene expression allowing for plant growth
- involved in phototropism
- upregulates expression of expansins
- causes transport of H= ions from cytoplasm to cell wall
Outline functions of auxin in roots vs shoots
- IN ROOTS: inhibits cell elongation
- IN SHOOTS: triggers cell elongation
Define phytochrome
leaf pigments used by plant to detect periods of light and darkness
Define photoperiodism
- response of plant to relative lengths of light & darkness
Discuss the main structures of a flower
- stigma: collects pollen
- style: long tube that holds up stigma to allow it to come in contact w/ pollen
- ovary: contains ovule & female gametes - this is where fertilisation occurs
- filament: long, thin tube that holds up the anther
- anther: where the male gametes are produced
- petals: attract pollinators
- sepal: a defensive organ that encloses & protects the developing reproductive structures
Term for female plant organs
PISTIL
Term for male plant organs
STAMEN
Structures of seed
- testa: outer seed coat that protects the embryonic plant
- micropyle: small pore in outer covering of seed that allows for passage of water
- cotyledon: contains food stores for seed & forms embryonic leaves
- plumule: embryonic shoot (also called epicotyl)
- radicle: embryonic root
What causes Pr to convert into Pfr?
absorption of red light (~660 nm)
What do short day plants need in order to flower?
they require night period to exceed a critical length
- Pfr INHIBITS flowering in short-day plant
What doe long-day plants require in order to flower?
they require the night to be LESS THAN a critical length
- Pfr ACTIVATES flowering in long-day plants
What is the advantage if end-product inhibition?
- intermediates do not build up
- helps to regulate levels of reactants & products
- once concentration of products falls, enzyme can return to catalysing the reaction, allowing reaction to begin once again
State example of negative feedback mechanism in metabolic reactions
end-product inhibition
Outline the key stages of glycolysis
- occurs in cytoplasm of cell & produces small quantity of ATP
- molecule of glucose becomes phosphorylated by binding of 2 phosphates from ATP
- forms HEXOSE BIPHOSPHATE
- causes its bonds to weaken
- splits into 2 3-C molecules to produce 2 TRIOSE PHOSPHATES
- 2 atoms of H removed from each triose phosphate –> OXIDATION
- 2 NADs –> 2 reduced NADs
- energy released converts 2 ADP –> 2 ATP
- 2 molecules of pyruvate are formed
State the products of glycolysis in mammals & bacteria
- lactate (in the muscles)
- known as LACTIC FERMENTATION
State the products of glycolysis in yeasts & plants
- ethanol & CO2
- alcoholic fermentation
Outline the link reaction
- occurs in matrix of mitochondria
- pyruvate loses a carbon atom in the form of CO2 (decarboxylation)
- loses electrons (hydrogen) & thus becomes oxidised
- NAD is reduced to NADH
- OXIDATIVE DECARBOXYLATION
- combines w/ an acetyl group to form acetyl-co-A
Outline the key stages in the Krebs Cycle
- 2C acetyl-co-A enters into Krebs cycle in matrix of mitochondria
- 4-C accepts 2C acetyl fragment from acetyl co-A to form 6C
- decarboxylation of 6C compounds –> 2x loss of CO2
- oxidation of 6C releases H atoms
- reduction of NAD & FADH (4 x oxidation reactions in total)
- substrate level phosphorylation (1 ATP produced per pyruvate - ADP –> ATP)
What is produced per GLUCOSE molecule in the Krebs Cycle (only, not including glycolysis or link reaction)?
- 4CO2
- 2 ATP
- 6 NADH + H+
- 2 FADH2
Define chemiosmosis.
- the use of a proton/electrochemical gradient to generate ATP (conversion of ADP into ATP) when protons diffuse back into matrix
What is the role of oxygen in cell respiration?
- acts as final electron acceptor
- is REDUCED
- removes de-energised electrons to prevent chain from becoming blocked
- binds free protons in matrix to form water
- maintains hydrogen gradient
What would happen if oxygen was not present in ETC for cell respiration?
- hydrogen carriers cannot transfer energised electrons to chain
- ATP production is halted
- reduced NAD NOT converted back into NAD
Outline the structure/function relationship of mitochondria.
- cristae: infoldings of plasma membrane - provide large SA for oxidative phosphorylation
- matrix: jelly-like fluid that contains enzymes for use in Krebs cycle + link reaction
- outer membrane: isolates the mitochondria from the rest of the cell – creates compartment w/ ideal conditions for aerobic respiration
- inner membrane: contains ETC & ATP synthase which carry out oxidative phosphorylation
- intermembrane space: small volume to enable rapid build-up of protons in chemiosmosis
- 70S ribosomes: used to synthesise proteins involved in aerobic respiration
Define photophosphorylation.
the conversion of ADP to ATP using the energy of sunlight by activation of PSII
Outline the photolysis of water.
- water molecules are in the thylakoid space
- photon of light causes bonds within water molecules to break
- leads to splitting of water molecule
- oxygen is released as waste product
- hydrogen ions contribute to proton gradient
Outline the key stages of the Calvin Cycle
- part of light-independent reactions
- occurs in stroma
- RuBP, a 5C compounds is CARBOXYLATED (CO2 added)
- forms an unstable 6-C compound
- Rubisco catalyses this reaction
- splits into 3C compound (glycerate-3-phosphate)
- glycerate-3-phosphate to triose phosphate by ADDING HYDROGEN
- using NADPH
- triose phosphate (3C) converted to form hexose / glucose
- some of the triose phosphate goes to making more RuBP
- FOR EVERY 6 MOLECULES OF TRIOSE PHOSPHATE FORMED, 5 ARE CONVERTED INTO RuBP
- 1 is used is produce 1/2 glucose
Outline the structure/function relationship of chloroplasts.
- stroma: contains enzymes for Calvin Cycle & large quantities of Rubisco
- Granum: stack of thylakoids for absorption as many of the available photons of light as possible
- thylakoid membranes: provide large total SA for light-absorbing photosystems –> also provide a site for electron flow, generation of a proton gradient & chemiosmosis
- 70S ribosomes: allow synthesis of proteins inside chloroplasts
- chloroplast envelope: creates compartment in which enzymes & other components of photosynthesis can be concentrated
- starch grain: for storage of carbohydrates produced by photosynthesis util it is exported from chloroplast
Outline the structure/function relationship of chloroplasts.
- stroma: contains enzymes for Calvin Cycle & large quantities of Rubisco
- Granum: stack of thylakoids for absorption as many of the available photons of light as possible
- thylakoid membranes: provide large total SA for light-absorbing photosystems –> also provide a site for electron flow, generation of a proton gradient & chemiosmosis
- 70S ribosomes: allow synthesis of proteins inside chloroplasts
- chloroplast envelope: creates compartment in which enzymes & other components of photosynthesis can be concentrated
- starch grain: for storage of carbohydrates produced by photosynthesis util it is exported from chloroplast
Examples of non-coding sequences of DNA.
- REGULATING GENE EXPRESSION –> e.g. sites where proteins can bind that are promoters or repressors of transcription
- INTRONS –> removed during post-transcriptional modification (in eukaryotes)
- TELOMERES –> repetitive base sequences at ends of chromosomes –> protect genes
- GENES FOR tRNA & rRNA –> produces tRNA & ribosomal RNA that forms ribosome
Explain tRNA activation.
- tRNA-activating enzymes recognize specific tRNA molecules by their SHAPE + CHEMICAL PROPERTIES
- enzyme-substrate specificity e.g.
- ATP + appropriate amino acid & tRNA bind to active site of activating enzyme
- a pair of phosphates is released from ATP & the remaining AMP bonds to amino acid
- raises its energy level –> allows the amino acid to bond to tRNA
Discuss the structure of nucleosomes.
- 8 histones in core have N-terminal tails that extend outward
- during condensation of chromosomes, the tails of histones in adjacent nucleosomes link up
- & pull chromosomes together –> supercoiling
- N terminal tails reversibly modified by adding ACETYL or METHYL groups
- prevents adjacent nucleosomes from packing together
- binding of DNA to nucleosome core is loosened when H1 protein is removed
Describe the function of nucleosomes.
- control which sections of chromosomes are condensed / decondensed
- during interphase, changes to nucleosome allow chromosomes to decondense
- allows access to DNA by polymerase enzymes (Replication/transcription)
Discuss transcription & gene expression.
- happens in cytoplasm
- involves promoter = base sequence close to start of gene
- repressor proteins can prevent transcription
- epigenetics = environment can trigger heritable changes
- methylation
- total number of proteins an organism can produce may be increased by ALTERNATIVE SPLICING
- hormones/chemical env. can affect gene expression e.g. auxin
- nucleosomes limit accessibility of transcription factors to DNA (in eukaryotes)
How does transcription differ in prokaryotes & eukaryotes?
- RNA polymerase binds to promoter in prokaryotes
- in eukaryotes, proteins called transcription factors bind FIRST to promoter which allows RNA polymerase to initiate transcription
Define proteome.
all the proteins produced by a cell, tissue, or organism –> variable
- it is unique because of differences in activity + amino acid sequences of proteins
Define genome.
all of the genes in an organism –> fixed
Describe the structure of tRNA.
- double stranded sections with base pairing
- triplet of bases called an anticodon, in a loop of 7 bases + 2 other loops
- the base sequence CCA at the 3’ terminal, which forms site for ATTACHING an amino acid
Describe the structure of ribosomes.
- proteins & ribosomal RNA molecules (rRNA) both form part of the structure
- 2 sub-units, 1 small 1 big
- a binding site for mRNA on SMALL subunit
- 3 binding sites for tRNA on LARGE subunit
Describe the structure of ribosomes.
- proteins & ribosomal RNA molecules (rRNA) both form part of the structure
- 2 sub-units, 1 small 1 big
- a binding site for mRNA on SMALL subunit
- 3 binding sites for tRNA on LARGE subunit
What is the A site on the ribosome?
for tRNA bringing in an AMINO ACID
What is the P site on the ribosome?
for tRNA carrying the growing POLYPEPTIDE
What is the E site for on the ribosome?
for the tRNA about to EXIT the ribosome
What is a conjugated protein?
a protein with a prosthetic group
What are polypeptides?
unbranched chains of amino acids
Benefits of mRNA splicing (removing introns)
Splicing of mRNA increases the number of different proteins an organism can produce.
What are polysomes?
a cluster of ribosomes at different points along mRNA that produce multiple copies of the polypeptide
primary structure
number & sequence of amino acids in polypeptide
secondary structure
formation of alpha helices & beta pleated sheets stabilised by hydrogen bonding
- alpha helices represented by HELICAL RIBBONS
- beta pleated sheets represented by arrows
tertiary structure
the further folding of the polypeptide stabilised by interactions b/w R groups
- R groups can be polar / hydrophobic
- intramolecular bonds b/w amino acids
quaternary structure
linking of 2 or more polypeptides to form a single protein
- same types of intramolecular bonds exist as in tertiary structure (e.g. ionic, covalent)
- hydrophobic interactions, disulphide bridges (in both)
- may have prosthetic group –> non-polypeptide structure
What is a disulphide bridge?
a covalent bond
- a disulfide refers to a functional group with the structure R−S−S−R′
- form b/w pairs of cysteines
Outline mechanisms by which transcription is regulated.
- promoters
- proteins that bind to specific base sequences (promoter or operator)
- nucleosome supercoiling
- methylation of DNA
What is a ribozyme?
RNA enzyme involved in splicing of mRNA
Outline processes involved in post-transcriptional modification.
- introns removed
- exons spliced together
- addition of a methyl group to the 5’-end of the transcribed RNA
- polyadenylation describes the addition of a long chain of adenine nucleotides (a poly-A tail) to the 3’-end of the transcript
Outline processes involved in post-transcriptional modification.
- introns removed
- exons spliced together
- addition of a methyl group to the 5’-end of the transcribed RNA
- polyadenylation describes the addition of a long chain of adenine nucleotides (a poly-A tail) to the 3’-end of the transcript
What is alternative splicing?
- particular exons of a gene may be included within or excluded from the final, processed messenger RNA (mRNA) produced from that gene
- This means the exons are joined in different combinations, leading to different (alternative) mRNA strands
- proteins translated from alternatively spliced mRNAs will contain differences in their amino acid sequence and, often, in their biological functions
Outline the extension of the stem in plants
a. apical meristem (of shoot/stem) produces cells/elongates the stem
OR
cell division/mitosis in tip/apex of shoot/stem;
b. auxin stimulates cell/stem growth/extension/enlargement;
c. elongation of cells causes stem to grow (in length);
Explain how some plant species are able to respond to changes in their abiotic environment and flower at a precise time of the year.
- genes for flowering are activated
- shoot apex changes from producing leaves to flowers
- daylength / duration of day/night detected
- short day plants in winter, long day plants in summer
