Topic 3: Voice of the Genome Part 1

Question 1

label a eukaryotic cell

Answer 1

Question 2

list different units of measurement from largest to smallest

Answer 2

metre - m
millimeter - mm
micrometer - µm
nanometre - nm

Question 3

what equation links image size, magnification and actual size

Answer 3

image size = actual size x magnification

Question 4

list the double membrane bound organelles

Answer 4

nucleus, nucelar envelope, mitochondria, chloroplast

Question 5

list the single membrane bound organelles

Answer 5

vacuole, lysosome, Golgi apparatus, endoplasmic reticulum

Question 6

describe the nucleus and it’s function

Answer 6

its a large organelle surrounded by a nuclear envelope which contains many pores

the nucleus contains chromatin (made from DNA and proteins) the nucleolus which makes ribosomes

it controls the cells activities, the pores allow substances to move between the nucleus and cytoplasm

Question 7

describe a lysosome and it’s function

Answer 7

its a round organelle surrounded by a membrane, with no clear internal structure

• contains digestive enzymes that can be used to digest invading cells/to break down worn out components of the cell

after digesting, the lysosome fuses with the cell surface membrane and the content of the lysosome are released via excytosis

Question 8

describe a ribosome and it’s function

Answer 8

a very small organelle that either floats free in the cytoplasm or is attached to the rough endoplasmic reticulum
it is made of proteins and RNA
it is not membrane bound

it’s the site where proteins are made

ribosome

Question 9

describe the rough endoplasmic reticulum and its function

Answer 9

its a system of membranes enclosing a fluid filled space, the surface is covered in ribosomes

it folds and processes proteins that have been made at the ribosomes

Question 10

describe the smooth endoplasmic reticulum and its function

Answer 10

its a system of membranes enclosing a fluid filled space

it synthesises and processes lipids

Question 11

describe the Golgi apparatus and its function

Answer 11

its a group of fluid filled, membrane bound, flattened sacs
vesicles can often been seen at the edges of the sacs

it modifies and packages new lipids and proteins, it also makes lysosomes

Question 12

describe mitochondrion and their function

Answer 12

they’re usually oval-shaped, they have a double membrane

they are the site of aerobic respiration, where ATP is produced
they’re found in large numbers in cells that are very active and require a lot of energy

Question 13

describe a centriole’s structure and it’s function

Answer 13

2 of them are a centrosome

small hollow cylinders made of microtubules, found in animal cells and some plant cells

they are involved with the separation of chromosomes during cell division

Question 14

outline the transport of proteins in cells

Answer 14

1. proteins (polypeptide chains) are made at ribosomes

• ribosomes on the rough endoplasmic reticulum make proteins that are excreted/attached to the cell membrane
• ribosomes that are free in the cytoplasm make proteins that stay in the cytoplasm

2. the new proteins produced at the rough endoplasmic reticulum are folded and processed, they form a 3D shape while in the rough ER
3. these proteins are transported in vesicles from the rough ER into the Golgi Apparatus
4. the proteins may then be modified at the Golgi Apparatus eg. they may be trimmed or sugar may be added
5. the proteins enter more vesicles to be transported around the cell
   - vesicles containing extracellular enzymes fuse with the cell surface membrane and the enzymes are secreted

Question 15

describe the cell cycle

Answer 15

1. interphase

G1 - cell grows and DNA replicates
S - chromosomes replicate and start condensing to form chromatin
G2 - the cell prepares to divide, replicating organelles so that each set has a full set

2. mitosis

prophase - chromosomes condense, nuclear envelope begins breaking down, spindle fibres start forming

metaphase - the chromosomes line up down the equator of the cell, centrioles produce spindle fibres that attach to the centromeres of chromosomes

anaphase - the spindle fibres shorten and the chromatids and pulled to opposite poles of the cell, separated at the centromere which splits

telophase - a nuclear envelope begins to form around each set of decondensing chromosomes, spindle fibres break down

3. cytokinesis

physical process of the cytoplasm splitting into 2 to form 2 completely separate, genetically identical daughter cells

Question 16

label this sperm cell

Answer 16

Question 17

label this egg cell

Answer 17

Question 18

what adaptations does a sperm cell have

Answer 18

it has the acrosome - it is a type of lysosome that contains digestive enzymes (acrosin) to break down the egg cell’s zona pellucida

haploid nucleus - has 23 chromosomes so there will be 46 in the zygote after fertilisation

lots of mitochondria - needed for the release of energy through respiration for motility

flagella - allows the sperm to be motile

receptors on the sperm head - chemicals from the egg cell(?)

Question 19

what adaptations does an egg cell have

Answer 19

cytoplasm containing a store of energy - this provides energy for the dividing zygote after fertilisation

zona pellucida - a protective, jellylike layer, it forms an impenetrable barrier after one sperm nucleus enters the cell

Question 20

what is the acrosome reaction

Answer 20

it occurs during fertilisation; the acrosome has to fuse to the sperm cell’s membrane and acrosin is then released via exocytosis so that they can digest through the zona pellucida

this allows the sperm to fuse with the cell surface membrane of the egg and the nucleus of the sperm is released into the egg

Question 21

what is the cortical reaction

Answer 21

it occurs immediately after the sperm cell fuses with the egg cell membrane and the acrosome reaction

vesicles known as cortical granules (located in the cytoplasm, next to the membrane) fuse with the cell surface membrane of the egg

the granules contain enzymes (proteases) that cause the zona pellucida harden and thicken, preventing any other sperm from fusing with the membrane

Question 22

label this prokaryotic cell

Answer 22

Question 23

describe the cytoplasm of a prokaryotic cell

Answer 23

it has no membrane-bound organelles and contains ribosomes that are smaller than in a eukaryotic cell

Question 24

describe the cell/plasma membrane in a prokaryotic cell

Answer 24

it is mainly made of lipids and proteins, it controls the movement of substances into and out of the cell; same as eukaryotic

Question 25

describe the cell wall in prokaryotic cells

Answer 25

the cell wall supports the cell and prevents shape changing, it’s made of a polymer, murein aka peptidoglycan, which is a glycoprotein

Question 26

describe pili on prokaryotes

Answer 26

pili help prokaryotes to stick to other cells and they can be used in the transfer of genetic material between cells

only on some prokaryotes

Question 27

describe the capsule on prokaryotes

Answer 27

it’s only found on some prokaryotes, eg. bacteria
it is made up of secreted slime and helps to protect bacteria from attack from immune cells

Question 28

describe mesosomes in prokaryotes

Answer 28

they are inward folds in the plasma membrane
their function is still being debated by scientists

they either:
- play a role in various cell processes
- are artefacts produced when cells are prepared to be viewed with an electron microscope

Question 29

describe plasmids in prokaryotes

Answer 29

they are small loops of DNA that aren’t part of the main, circular DNA molecule

they contain genes for things like antibiotic resistance and can be passed between prokaryotes; they aren’t always present but some can also have several plasmids

Question 30

how is DNA kept in a prokaryotic cell

Answer 30

prokaryotic cells don’t have a nucleus, so the DNA floats freely in the cytoplasm

it’s circular DNA, present as one long coiled-up strand and is not attached to any histone proteins

it is NOT single stranded

Question 31

describe the flagellum

Answer 31

it’s a long, hair-like structure that rotates to make the prokaryotic cell move; not all have one and some can have more than one

Question 32

what are the features of a prokaryotic cell

Answer 32

ribosomes
cytoplasm
plasma/cell membrane
cell wall
pili
capsule
mesosomes
plasmids
circular DNA
flagellum

Question 33

what are the main features of an animal cell

Answer 33

plasma (cell surface) membrane
rough endoplasmic reticulum
nucleolus
centriole
nucleus
smooth endoplasmic reticulum
lysosome
ribosome
nuclear envelope
Golgi apparatus
cytoplasm
mitochondrion

Question 34

what is the mitotic index

Answer 34

the proportion of cells undergoing mitosis

mitotic index = no. of cells with visible chromosomes/total no. of observed cells

Question 35

how is an electron microscope different to a light microscope

Answer 35

it has a higher resolution and therefore a higher magnification because electrons have a smaller wavelength than light

Question 36

why do we need mitosis

Answer 36

it is needed for growth of cells and to replace damaged cells, it produces genetically identical cells so is used for asexual reproduction (cloning)

Question 37

devise an experiment to observe mitosis

Answer 37

1. cut 1cm from the tip of a growing root
2. prepare a boiling tube containing 1M hydrochloric acid and put in a 60˚C water bath
3. transfer the root tip into the boiling tube and incubate for 5 minutes
4. rinse it well with cold water using a pipette and leave the tip on a paper towel to dry
5. place the root tip on a microscope slide and cut 2mm from the very tip, get rid of the rest
6. use a mounted needle to break open the tip and spread the cells out thinly
7. add a drop of toluidine blue stain and leave for a few minutes, the stain makes the chromosomes easier to see under microscope
8. place a cover slip over cells, push down firmly and squash the tissue to make it thinner and allow light to pass through, don’t smear it sideways as chromos will be damaged
9. look at all the stages of mitosis under a light microscope

calculate the mitotic index using:
mitotic index = no. cells with visible chromosomes/total no. cells observed

Question 38

how do sperm reach the site of the acrosome and cortical reaction

Answer 38

sperm is deposited high in the female vagina, near the cervix entrance
they then have to make their way up and through the cervix and uterus into one of the oviducts which is where fertilisation may occur

Question 39

outline interphase

Answer 39

G1 - cell grows and DNA replicates
S - chromosomes replicate and start condensing to form chromatin
G2 - the cell replicates organelles so that each set has a full set

Question 40

how many stranded is plasmid DNA

Answer 40

double stranded