Topic 3 completed Flashcards
what are the 12 organelles found in an animal cell?
rough endoplasmic reticulum, smooth endoplasmic reticulum, Golgi apparatus, ribosomes, nucleus, nucleolus, centriole, plasma membrane, lysosome, nuclear envelope, cytoplasm, mitochondrion
what are the 4 features that all living cells have?
cell surface membrane, cytoplasm, ribosomes, DNA
what type of cell are animal cells?
eukaryotic
describe the nucleus
large organelle surrounded with nuclear envelope (double membrane), contains chromatin and the nucleolus
what is the function of the nucleus?
controls cells activities by controlling transcription, nucleolus makes ribosomes
describe the lysosome
round organelle, surrounded with a membrane, has no clear internal structure
what is the function of a lysosome?
contains digestive enzymes, used to digest invading cells or break down worn out components of the cell
what happens to the lysosome after its contents has been digested?
lysosome fuses with cell membrane
contents of lysosome released from the cell via exocytosis
describe a ribosome
small organelle, can float free or be attached to RER, made up of proteins and RNA, no membrane
what is the function of a ribosome?
site of translation (where proteins are made)
describe a rough endoplasmic reticulum
system of membranes enclosing a fluid- filled space, surface covered with ribosomes
what is the function the rough endoplasmic reticulum?
folds and processes proteins which have been made at the ribosomes
describe the smooth endoplasmic reticulum
a system of fluid filled membranes enclosing a fluid filled space
what is the function of the smooth endoplasmic reticulum?
synthesises and processes lipids
describe the golgi apparatus
a group of fluid filled, membrane bound, flattened sacs, vesicles seen at edges
what is the function of the golgi apparatus?
processes and packages new lipids and proteins, and makes lysosomes
describe the structure of the mitochondrion
oval shaped, double membrane, inner membrane folds into the matrix to form cristae, matrix contains enzymes for respiration
what is the function of a mitochondria?
site of aerobic respiration, where ATP is produced, large numbers are found in very active cells that require lots of energy
describe a centriole
small, hollow structures, made of microtubules, found in animal and some plant cells
what is the secretory pathway?
ribosomes produced in nucleolus
proteins made at a ribosome
proteins produced at rough ER are folded and processed (e.g. sugar chains added) in the rough ER
transported from the rER to the Golgi apparatus in vesicles
Golgi modifies protein (carbohydrates added to form glycoprotein)
Golgi packages protein into vesicle to leave the cell
vesicle fuses with cell membrane and proteins leaves cell via exocytosis
If a protein is made on a ribosome on the RER, where does it go?
out of the cell or into cell membrane
If a protein is made on a free ribosome, where does it go?
it stays in the cytoplasm
what are the 9 features of a prokaryotic cell?
70s ribosomes, flagella, circular DNA, plasmids, mesosomes, cell walls (peptidoglycan for bacteria), slime capsule, pili, plasma membrane
does the cytoplasm of a prokaryote have membrane bound organelles?
no
what is the function of flagella?
rotate to make the cell move
some cells have multiple and some will have none
describe the DNA in a prokaryotic cell
free floating circular DNA (one long coiled-up strand) not attached to any histone proteins
what are plasmids?
small, circular loops of DNA which contain genes for things such as antibiotic resistance and can be passed easily between prokaryotes
what are mesosomes?
inward folds of plasma membrane- unsure of function but may have a role in cellular processes such as respiration
what is the function of a slime capsule?
helps to protect bacteria from immune system cells
what are pili?
short hair-like structures which help stick prokaryotes to other cells and used in gene transfer between cells
what are the advantages of light microscopes?
uses light so sample can be living
cheaper
smaller
what are the advantages of an electron microscope?
higher resolution- gives a more detailed image
high max magnification- can see small organelles such as lysosomes
what are the 2 types of electron microscope?
transmission electron microscope- denser parts absorb more electrons and look darker, give high resolution images, thin samples only
scanning electron microscope- can give 3D images, thick specimens, lower resolution
define a tissue
a group of similar cells that are specially adapted to work together to carry out a particular function
give an example of a plant tissue
xylem tissue
define organ
a group of different tissues that work together to perform a particular function
give an example of a plant organ
the leaf
what are the layers in a leaf cross section?
waxy cuticle
upper epidermis
palisade mesophyll
spongy mesophyll
lower epidermis
define organ system
a group of organs with related functions working together to perform body functions within the body
give an example of an organ system
the circulatory system- made up of the heart, arteries, veins and capillaries to supply the body with blood
what does mitosis produce?
2 genetically identical diploid daughter cells needed for growth, repair and asexual reproduction
what are the stages of the cell cycle?
interphase and mitosis
what are the stages of interphase?
gap phase 1, synthesis, gap phase 2
what happens in gap phase 1?
cell grows and new organelles and proteins made
what happens in synthesis?
cell replicates its DNA, ready to divide by mitosis
what happens in gap phase 2?
cell keeps growing, new organelles and proteins needed for cell division are made, cell prepares to divide
what are the stages of mitosis?
prophase, metaphase, anaphase, telophase
what happens during prophase?
chromosomes condense, centrioles move to poles of cell and form a network of spindle fibres, nuclear envelope breaks down
what happens in metaphase?
chromosomes line up along middle of cell and spindle fibres attach to their centromere
what happens during anaphase?
centromeres divide- separating sister chromatids, spindle fibres contract pull chromatids to poles centromere first (V-shape)
what would happen if the spindle fibres couldn’t shorten?
chromatids cannot be separated, anaphase cannot occur, mitosis will not be completed
what happens during telophase?
chromatids uncoil in poles, now called chromosomes, nuclear envelopes form around the 2 groups, cytoplasm divides (cytokinesis)
which chemical signals are used to move from one stage of mitosis to the next?
cyclins
what are spindle fibres made from?
microtubules
why is HCl used in the mitosis core practical?
to break down middle lamella, to allow cells to be separated, to allow light to pass through
why is a stain used in the mitosis core practical?
makes chromosomes visible, so stages of mitosis can be identified
how many chromosomes does a human gamete have?
23
how is an egg cell adapted for its function?
zona pellucida- protective glycoprotein layer that sperm have to penetrate, hardens once they have entered, prevents polyspermy
haploid nucleus- containing 23 chromosomes
follicle cells- protective layer
cortical granules- release substances which cause the zona pellucida to harden
cytoplasm- contains nutrients and provides energy for the zygote after fertilisation
how is a sperm cell adapted for its function?
mid piece contains may mitochondria to provide flagellum lots of energy to rotate and move the cell (through respiration)
acrosome contains digestive enzymes which breakdown the zona pellucida and allow the sperm to fertilise the cell
haploid nucleus- contains 23 chromosomes
flagellum for movement
what are the stages of fertilisation?
sperm makes contact with the zona pellucida (in the oviduct) and the acrosome reaction occurs (acrosome fuses with sperm cell membrane, digestive enzymes are released, enzymes breakdown zona pellucida)
sperm head fuses with the cell membrane which triggers the cortical reaction (egg cell releases cortical granules from vesicles into the space between the cell membrane and the zona pellucida)
the cortical granules cause the zona pellucida to thicken and harden, preventing polyspermy
the sperm nucleus enters the cell and fuses with the nucleus of the egg cell
a zygote forms
what does meiosis produce?
4 genetically different haploid daughter cells
what are the stages of meiosis?
1- DNA replicates so there’s 2 identical copies of each chromosome
2- DNA condenses into double armed chromosomes
3- chromosomes arrange into homologous pairs
4- first division homologous pairs separated, halving chromosome number
5- second division sister chromatids separated
what 2 processes make gametes genetically different?
crossing over of chromatids and independent assortment of chromosomes
how does crossing over of chromatids create genetic variation?
before the first division the homologous pairs pair up
two of the chromatids in each homologous pair twist around each other
the twisted bits break off their original chromatid and rejoin onto the other, recombining their genetic material
the chromatids have the same genes but a different combination of alleles
how does independent assortment create genetic variation?
the chromosomes are randomly sorted into each cell so different combinations of maternal and paternal chromosomes, with different alleles go into each cell
what is meant by the term linked in genetics?
genes with loci on the same chromosomes are linked because they will stay together during independent assortment and are more likely to stay together through crossing over so the alleles are likely to be inherited together
define locus
the position of a gene on a chromosome
when is a characteristic sex-linked?
when the locus of the allele that codes for the characteristic is on a sex chromosome
why are most genes on the X chromosomes only found on the x and not the Y as well?
the X chromosome is much bigger (the Y chromosome doesn’t have enough room)
why are males more likely than females to shown recessive genotypes for genes that are sex-linked?
males only have one X chromosome and so only have one allele for sex linked genes. Males have 50% chance of being recessive but females 25%
what are stem cells?
unspecialised cells that can develop into other types of cell with unlimited divisions
define totipotency
the ability to differentiate into all cell types
define pluripotency
the ability of a stem cell to produce all the specialised cells in an organism but not extraembryonic cells
what is the source of pluripotent stem cells?
blastocyst
what are the 2 main differences between benign and malignant tumours?
malignant are cancerous and can spread (metastasize) but benign aren’t cancerous and don’t spread
what type of stem cells can give rise to a whole organism?
totipotent, not pluripotent
which type of stem cell has some inactivated genes?
pluripotent
which type of stem cell has no inactivated genes?
totipotent
how do stem cells become specialised?
stem cells all contain the same genes but not all are active (and expressed)
under different conditions, some genes are activated and some are inactivated
mRNA is only transcribed from active genes
the mRNA is then translated into proteins
the proteins modify the cell
changes caused by the proteins make the cell specialised and the changes are difficult to reverse so a cell has to stay specialised
what are transcription factors?
proteins that bind to operator regions on DNA and activate or deactivate genes
what causes transcription factors to bind to promoter regions?
stimuli (hormones) or changes in external or internal environment (blood pH, temperature)
what are the 2 types of transcription factors?
activators- increase the rate of transcription by encouraging RNA polymerase bind to the DNA
repressors- decrease the rate of transcription by preventing RNA polymerase from binding and so stopping transcription
how does gene expression differ between eukaryotes and prokaryotes?
in eukaryotes transcription factors bind to specific DNA sites near the start of their target genes
in prokaryotes transcription factors bind to operons
what is an operon?
a section of DNA that contains a cluster of structural genes, that are transcribed together as well as control elements and sometimes a regulatory gene
what does RNA polymerase bind to on an operon?
the promoter region
where does the repressor protein bind to on the lac operon?
the operator region
what do structural genes code for?
useful proteins such as an enzyme
what are the 2 types of control element in an operon and what do they do?
promoter- a DNA sequence located before the structural genes, where RNA polymerase binds to
operator- a DNA sequence that transcription factors bind to
what do regulatory genes code for?
an activator or repressor
what happens at the lac operon in E.coli when lactose is not present?
the regulatory gene (lacI) is transcribed to produce lac repressor protein
repressor protein binds to operator
this blocks RNA polymerase from transcribing the rest of the operon as RNA polymerase cannot bind the the promotor
so no enzyme is produced
what happens at the lac operon in E.coli when lactose is present?
the regulatory gene (lacI) is transcribed to produce lac repressor protein
lactose binds to the repressor protein and changes its shape, this prevents the repressor protein binding to the operator site
RNA polymerase binds to promotor region and transcribes structural genes to produce B-galactosidase
how are/will stem cells be used in medicine?
leukaemia- bone marrow transplants mean damaged/dead stem cells can be replaced
spinal cord injuries- stem cells could be used to repair damaged nerve tissue
heart disease- stem cells could be used to replace damaged heart tissue
what are the 2 types of human stem cells?
adult and embryonic
describe adult stem cells
found in bone marrow
obtained by inserting a needle into the centre on a bone- low risk but painful
aren’t as flexible as embryonic as can only differentiate into a limited range of cells
less risk of rejection if using stem cells from the same person (different area)
describe embryonic stem cells
obtained from early embryos 4-5 days old
embryos created in a lab using IVF
the rest of the embryo is destroyed
can develop into all types of cell
what are the ethical issues of embryonic stem cells?
mean destruction of a viable embryo
some people believe right to life starts at fertilisation
regulatory bodies have been stablished for embryonic stem cell research, what do they do?
look at proposals of research to make sure the embryos are being used for a good reason and make sure research isn’t unnecessarily repeated
licensing and monitoring centres- to ensure only fully trained staff have access to the embryos
what is continuous variation?
when the individuals in a population vary within a range- there are no distinct categories
give 3 examples of continuous variation
mass, height, skin colour
what is discontinuous variation?
where there are two or more distinct categories and each individual falls into one category
give an example of discontinuous variation
blood group
what is monogenic?
when a characteristic is controlled by one gene- usually show discontinuous variation
what is polygenic?
when a characteristic is controlled by a number of genes at different loci- usually show continuous variation and is more common
what is variation in phenotype influenced by?
genotype and the environment
give 4 ways in which the environment affects the phenotype
nutrition- can increase height
Monoamine Oxidase (MAOA)- enzyme which breaks down monoamines, low MAOA levels are linked to mental health issues, levels can be reduced by smoking
diet- can increase the risk of some cancers
temperature- changes in temperature lead to some artic animals having darker hair in the summer and lighter hair in the winter
what is epigenetic control?
controls which genes are expressed by adding or removing chemical groups from the DNA - altering the phenotype
what is methylation?
adds a methyl group to the DNA
always added to a CpG site (where cytosine and guanine are next to each other in the DNA)
increased methylation prevents RNA polymerase binding to the DNA and so prevents transcription- gene is repressed/inactivated
what are histones?
proteins which DNA wrap around to form chromatin (which makes up chromosomes) if the chromatin is highly condensed the enzymes cannot bind and transcription does not occur
what is acetylation?
when the histones are acetylated the chromatin is less condensed, RNA polymerase can bind, transcription occurs, genes are activated
when the acetyl groups are removed the chromatin becomes highly condensed, RNA polymerase cannot bind, transcription doesn’t occur, gene repressed/ inactivated
can epigenetic changes be passed on through cell division?
sometimes it can be- this would mean the certain genes are activated or deactivated and the daughter cell will be equipped to deal with the changed environment in the same as the original cell
