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SNAB Biology > Topic 3 > Flashcards

Topic 3 Flashcards

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
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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
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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.
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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.
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5
Q

Nucleolus

A
  • A dense body within the nucleus where ribosomes are made.
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6
Q

Rough Endoplasmic Reticulum (rER)

A
  • A system of interconnected membrane-bound, flattened sacs.
  • Ribosomes are connected to the outer surface.
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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
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8
Q

Cell surface membrane (plasma membrane)

A
  • Phospholipid bilayer containing proteins and other molecules forming a partially permeable barrier.
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9
Q

Smooth endoplasmic reticulum

A
  • does not have any attached ribosomes

- makes lipids and steroids (e.g. reproductive hormones).

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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.
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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
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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.
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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.

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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.
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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
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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.
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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.
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18
Q

Fusion of nuclei

A

The sperm nucleus that enters the egg fuses with the egg nucleus to form a fertilised egg

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19
Q

Locus

A

the location of genes on a chromosome

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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.
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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
Q

Mitosis - Telophase

A

– Chromosomes unravel
– Two nuclear envelopes reform
- spindle breaks down

26
Q

Cytoplasmic division in mammals

A

a ring of protein filaments bound to the inside of the cell surface membrane contract until the cell splits into two new cells.

27
Q

Cytoplasmic division in plants

A

plant cells synthesise a new cell plate between the two new cells.

28
Q

Flagella

A

long hair like structure that rotates to make the prokaryotic cell move

29
Q

Circular DNA

A
  • Prokaryotic cells have no nucleus
  • The DNA is instead circular
  • It is one coiled up strand not attached to any histone proteins
30
Q

Plasmid

A

Small loops of DNA not part of the circular DNA

contain genes for things like antibiotic resistance and can be passed between prokaryotes

31
Q

Mesosome

A
  • inward folds in the plasma membrane
32
Q

Capsule

A
  • Made up of secreted slime

- Protects bacteria from any attack by cells of the immune system

33
Q

Pili

A
  • Short hair like structures
  • help prokaryotes stick to other cells
    can be used to transfer genetic material between cells
34
Q

Cell Wall

A
  • Supports the cell and prevents it from changing shape
  • made of the polymer murein
  • muerin is a glycoprotein
35
Q

Plasma Membrane

A
  • mainly made of lipids and proteins

- controls the movement of substances into and out of the cell

36
Q

Cytoplasm

A
  • has no membrane bound organelles
  • has small ribosomes
  • fluid-like substance present between the cell membrane and nucleus
37
Q

Squamous epithelium

A
  • Is a single layer of cells lining a surface

- found in many places including alveoli in the lungs

38
Q

Ciliated epithelium

A
  • a layer of cells covered in cilia

- found on surfaces where things need to be moved - e.g. in the trachea

39
Q

Cartilage

A
  • a type of connective tissue found in the joints

- shapes and supports the ears, nose and windpipe

40
Q

The leaf - structure

A
  • 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
Q

The lungs - structure

A
  • 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
Q

Totipotent

A

Can differentiate into all types of cells

43
Q

Pluripotent

A

Can differentiate into most types of cells

44
Q

Stem cells become specialised through differential gene expression

A
  • 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
Q

Transcription Factors

A
  • 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
Q

Activators

A
  • increase rate of transcription

- help RNA polymerase bind to the DNA and begin transcription

47
Q

Repressors

A
  • decrease rate of transcription

- prevent RNA polymerase from binding so stopping transcription

48
Q

Operons

A
  • 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
Q

Lac operon in E. coli

A

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
Q

DNA Methylation (epigenics)

A
  • 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
Q

Histone modification (epigenics)

A
  • 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 (11 decks)

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