1
Q
Features of Eukaryotic cells
A
- have discrete membrane-bound organelle.
- Larger cell diameters are 20 μm or more
- not all have a cell wall
- Have nuclei
2
Q
Features of Prokaryotic cells
A
- Bacteria and cyanobacteria (photosynthetic bacteria) together make up the prokaryote kingdom.
- Their cells do not have nuclei or membrane-bound organelle
3
Q
Mitochondrion (plural mitochondria):
A
- The inner of it’s two membranes is folded to form finger-like projections called cristae.
- The mitochondria are the site of the later stages of respiration.
4
Q
Nucleus
A
- Enclosed by an envelope composed of two membranes perforated by pores.
- Contains chromosomes and a nucleolus.
- The DNA in chromosomes contains genes that control the synthesis of proteins.
5
Q
Nucleolus
A
- A dense body within the nucleus where ribosomes are made.
6
Q
Rough Endoplasmic Reticulum (rER)
A
- A system of interconnected membrane-bound, flattened sacs.
- Ribosomes are connected to the outer surface.
7
Q
Ribosomes
A
- Made of RNA and protein
- small organelles
- found free in the organism or attached to the endoplasmic reticulum
- They are the site of protein synthesis
8
Q
Cell surface membrane (plasma membrane)
A
- Phospholipid bilayer containing proteins and other molecules forming a partially permeable barrier.
9
Q
Smooth endoplasmic reticulum
A
- does not have any attached ribosomes
- makes lipids and steroids (e.g. reproductive hormones).
10
Q
Golgi apparatus
A
- Stacks of flattened, membrane-bound sacs - cisternae
- formed by the fusion of vesicles from the ER
- Modifies proteins and packages them in vesicles for transport.
11
Q
Lysosome
A
- Spherical sac containing digestive enzymes bound by a single membrane
- Involved in the breakdown of unwanted structures within the cell and the destruction of whole cells when old cells are to be replaced or during development.
e. g. the acrosome
12
Q
Centrioles
A
- Hollow cylinders made up of a ring of nine protein microtubules
- (polymers of globular proteins arranged in a helix to form a hollow tube)
- help form the spindles during nuclear division
- involved in transport within the cell cytoplasm.
13
Q
Protein transport within cells - golgi apparatus and rER
A
- The rER’s ribosomes synthesise proteins and transports them to the golgi apparatus from the RER
- The Golgi apparatus receives proteins and lipids (fats) from the rough endoplasmic reticulum.
- It modifies some of them and sorts, concentrates and packs them into sealed droplets called vesicles.
- Depending on the contents these are despatched to one of three destinations:
Destination 1: within the cell, to organelles called lysosomes.
Destination 2: the plasma membrane of the cell
Destination 3: outside of the cell.
14
Q
The Ovum (egg cell)
A
- Large and incapable of independent movement.
- Wafted along the oviducts from the ovary to the uterus by ciliated cells lining the tubes and by muscular contractions of the tubes.
- The cytoplasm of the ovum contains proteins and lipid food reserves for a developing embryo.
- Surrounding the cell is a jelly-like coating called a zona pellucida.
15
Q
The Sperm cell
A
- Much smaller, and independently mobile.
- Mitochondria in the middle piece
- To enable it to swim the sperm has a long tail powered by energy released by the mitochondria
- The sperm are attracted to the ovum by the chemicals released by it
- The acrosome (found in the head of the sperm cell) is a lysosome
16
Q
acrosome reaction
A
- To penetrate the ovum the sperm’s acrosome releases digestive enzymes - which break down the zona pellucida of the ovum.
17
Q
cortical reaction
A
- a sperm fuses with and penetrates the membrane surrounding the egg
- chemicals released by the ovum cause the zona pellucida, to thicken, preventing any further sperm entering the egg.
18
Q
Fusion of nuclei
A
The sperm nucleus that enters the egg fuses with the egg nucleus to form a fertilised egg
19
Q
Locus
A
the location of genes on a chromosome
20
Q
Independent assortment
A
- During meiosis only one chromosome from each pair ends up in each gamete.
- The independent assortment of the chromosome pairs as they line up in during meiosis I is a source of genetic variation.
- This process is random: either chromosome from each pair could be in any gamete.
- This way of sharing chromosomes produces genetically variable gametes.
21
Q
Crossing over
A
- During the first meiotic division, homologous chromosomes come together as pairs and all four chromatids come into contact.
- At these contact points the chromatids break and re-join, exchanging sections of DNA.
- The point at which these chromatids break is called a chiasma (plural chiasmata),
- several of these often occur along the length of each pair of chromosomes, giving rise to a large amount of variation.
22
Q
Mitosis - Prophase
A
– Chromosomes condense (chromatids joined by centromere)
– Spindle fibres join to both centrioles
– Nuclear envelope breaks down
23
Q
Mitosis - Metaphase
A
– Centromeres attach to spindle fibres at the equator.
– Chromosomes line up
24
Q
Mitosis - Anaphase
A
– Centromeres split
– One chromatid from each chromosome is pulled to either end of the cell
25
Mitosis - Telophase
– Chromosomes unravel
– Two nuclear envelopes reform
- spindle breaks down
26
Cytoplasmic division in mammals
a ring of protein filaments bound to the inside of the cell surface membrane contract until the cell splits into two new cells.
27
Cytoplasmic division in plants
plant cells synthesise a new cell plate between the two new cells.
28
Flagella
long hair like structure that rotates to make the prokaryotic cell move
29
Circular DNA
- Prokaryotic cells have no nucleus
- The DNA is instead circular
- It is one coiled up strand not attached to any histone proteins
30
Plasmid
Small loops of DNA not part of the circular DNA
| contain genes for things like antibiotic resistance and can be passed between prokaryotes
31
Mesosome
- inward folds in the plasma membrane
32
Capsule
- Made up of secreted slime
| - Protects bacteria from any attack by cells of the immune system
33
Pili
- Short hair like structures
- help prokaryotes stick to other cells
can be used to transfer genetic material between cells
34
Cell Wall
- Supports the cell and prevents it from changing shape
- made of the polymer murein
- muerin is a glycoprotein
35
Plasma Membrane
- mainly made of lipids and proteins
| - controls the movement of substances into and out of the cell
36
Cytoplasm
- has no membrane bound organelles
- has small ribosomes
- fluid-like substance present between the cell membrane and nucleus
37
Squamous epithelium
- Is a single layer of cells lining a surface
| - found in many places including alveoli in the lungs
38
Ciliated epithelium
- a layer of cells covered in cilia
| - found on surfaces where things need to be moved - e.g. in the trachea
39
Cartilage
- a type of connective tissue found in the joints
| - shapes and supports the ears, nose and windpipe
40
The leaf - structure
- upper epidermis - covered in waterproof waxy cuticle to reduce water loss
- spongy mesophyll - full of spaces to let gas circulate
- palisade mesophyll - most photosynthesis occurs here
- xylem - carries water to the leaf
- phloem - carriers sugars away from the leaf
- lower epidermis - contains stomata to let air in and out for gas exchange
USPXPL
41
The lungs - structure
- Squamous epithelium tissue - surrounds the alveoli
- Fibrous connective tissue - helps to force air back out of the lungs when exhaling
- endothelium tissue - makes up the wall of capillaries, which surround the alveoli, and lines the larger blood vessels
42
Totipotent
Can differentiate into all types of cells
43
Pluripotent
Can differentiate into most types of cells
44
Stem cells become specialised through differential gene expression
- all stem cells contain the same genes
- not all are expressed because not all are active
- under the right conditions some are activated and some are inactivated
- mRNA is only transcribed for active genes
- the mRNA is then translated into proteins
- the proteins modify the cell —> determining the cell structure and the processes
- these changes cause the cell to become specialise/differentiate
45
Transcription Factors
- gene expression can be controlled by altering the rate of transcription of genes
- e.g. increased transcription produces more mRNA, which can be used to make more protein
- this is controlled by transcription factors - proteins that bind to DNA and activate or deactivate genes by increasing or decreasing the rate of transcription
e. g. activators and repressors
- in eukaryotes such as animals and plants the transcription factors bind to specific DNA sites near the start of target genes
- In prokaryotes control of gene expression often involves transcription factors binding to operons
46
Activators
- increase rate of transcription
| - help RNA polymerase bind to the DNA and begin transcription
47
Repressors
- decrease rate of transcription
| - prevent RNA polymerase from binding so stopping transcription
48
Operons
- a section of DNA that contains a cluster of structural genes
- all transcribed together, with control elements and sometimes a regulatory gene:
- structural genes: code for useful proteins such as enzymes
- control elements: include a promoter (located before the structural genes that RNA polymerase binds)
And
an operator (a DNA sequence that transcription factors bind to)
- regulatory gene: codes for an activator or repressor
49
Lac operon in E. coli
When lactose is NOT present
- the regulatory gene produces the lac repressor, which is a transcription factor that binds to the operator the site
- This blocks transcription because RNA polymerase can’t bind to the promoter and the proteins that digest lactose are not made
When lactose IS present
- lactose binds to the repressor changing its shape so that it can no longer bind to the operator site
- RNA polymerase can now begin transcription of the structural genes so that the lactose can be digested
50
DNA Methylation (epigenics)
- a methyl group is attached to the DNA coding for a gene
- it always attaches at the CpG site (cytosine and guanine bases are next to eachother)
- increased methylation changes the DNA structure so that proteins and enzymes needed for transcription can’t bind to the gene
- so the gene is not expressed
51
Histone modification (epigenics)
- histones are proteins that DNA wraps around to form chromatin, which makes up chromosomes
- chromatin can be highly condensed or less condensed
- how condensed chromatin is affects the accessibility of the DNA and whether or not the proteins and enzymes needed for transcription can bind to it
- addition of acetyl groups = less condensed and genes can be transcribed (genes are activated)
- removal of acetyl groups = highly condensed and DNA cannot be transcribed (genes are repressed)
SNAB Biology
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