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Voice Of The Genome Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What is the function of the smooth ER?

A

-synthesis of lipids + hormones

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2
Q

What is the function of the rER?

A

-synthesis of membrane bound/secreted proteins

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3
Q

The endoplasmic reticulum is a system of…

A

Interconnected membrane-bound flattened sacs (cisternae)

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4
Q

Which type of ER is covered in ribosomes?

A

Rough

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5
Q

The ER is connected with which organelle?

A

Nuclear membrane

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6
Q

what is the function of the Golgi apparatus?

A

-modification and packaging of proteins from transport

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7
Q

What is the structure of the Golgi apparatus?

A

-stacks if flattened membrane-bound sacs

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8
Q

What are vesicles?

A

-small membrane bound sacs for storage and transport of molecules

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9
Q

What is the function of the lysosome?

A

-breakdown materials in cells (also involved in apoptosis)

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10
Q

The lysosome has a ……………. Membrane

A

Single

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11
Q

The lysosome contains…

A

Digestive enzymes

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12
Q

What does the cytoskeleton do?

A

-gives the cell structure and allows cell to change shape
-helps with transport of vesicles around cell

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13
Q

What is endosymbiotic theory?

A

-some of organelles in eukaryotic cells were once prokaryotic microbes

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14
Q

How did the nucleus form?

A

-infolding of the plasma membrane

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15
Q

What are ribosomes like in mitochondria and chloroplasts?

A

-ancient bacteria

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16
Q

Describe images taken by an EM

A

-black and white
-highly contrasted

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17
Q

What is the main draw back of using an EM to study living things?

A

-thin layer
-only can view non-living things

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18
Q

What does the nucleus contain?

A

Genetic information (as chromatin)

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19
Q

The nucleus has a single/double membrane

A

Double

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20
Q

Does the nucleus have nuclear pores?

A

Yes

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21
Q

What is the nucleolus

A

-a dense area in nucleus where ribosomes are made

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22
Q

What is chromatin?

A

-combination of DNA and proteins (histones) that make up chromosomes

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23
Q

What is the function of mitochondria?

A

-site of aerobics respiration

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24
Q

Mitochondria has a …………… membrane

A

Double

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25
Q

What is the inner membrane of mitochondria folded into?

A

Cristae

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26
Q

What is the centrosome made of?

A

2 cebtrioles

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27
Q

What does the centrosome form?

A

The miotic spindle

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28
Q

How many pairs of centrosomes are there in each animal cell?

A

One

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29
Q

What are centrosomes made of?

A

-ring of protein called microtubules

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30
Q

what is the function of ribosomes?

A

-protien synthesis

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31
Q

What are ribosomes made of?

A

-rna
-protein

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32
Q

Where are the ribosomes?

A

-free in cytoplasm
-bound to er

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33
Q

What type of ribosomes are in eukaryotic cells?

A

80S

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34
Q

What is the function of the cell membrane?

A

-control of movement of molecules in and out of cell
-lipid bilayer

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35
Q

In a prokaryotic cell, what is the function of circular DNA?

A

-genetic information
(Not associated with proteins)

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36
Q

what is the plasmid

A

A small circle of DNA

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37
Q

what is the name for glycogen granules and lipid droplets in prokaryotic cells?

A

Food granules

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38
Q

What is the mesosome?

A

The infolding of cell membrane/site of respiration

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39
Q

What is the mesosome now considered to be due to?

A

-prep of slide rather than a real structure

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40
Q

What is the cell wall of a prokaryotic cell made of?

A

-peptidoglycan

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41
Q

what is the function of the capsule?

A

Slimy layer on surface for protection and to prevent dehydration

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42
Q

What are the pili?

A

-thin protein tubes
-allows bacteria to adhere to surfaces

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43
Q

What is the flagellum?

A

-hollow cylindrical thread-like structures
-rotates to the move the cell

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44
Q

What are the three types of bacteria?

A

-coccus
-bacillus
-spirochete

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45
Q

Do prokaryotic cells have membrane bound organelles?

A

No

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46
Q

What are examples of eukaryotic cells?

A

-animals
-plants
-protoctista

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47
Q

Where do proteins made on free ribosomes go?

A

-nucleus
-mitochondrion
-chloroplast
-peroxisome

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48
Q

Where do proteins made on the rER go to?

A

-secretory vesicles
-lysosome
-plasma membrane

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49
Q

What are cisternae?

A

-elongated membrane bound sacs

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50
Q

Describe the secretory pathway

A

-proteins destined for secretion are synthesised on rER
-proteins are folded in rER and modified

-proteins exit ER in a vesicles and are transported to the Golgi

-proteins travel through the Golgi (from cisterna to cisterns) where they are modified further

-proteins are packed into secretory vesicles that bud off Golgi and are transported to the cell membrane

-vesicles fuse with plasma membrane:
-secreted proteins exit cells by exocytosis
-transmembrane proteins stay in cell membrane

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51
Q

The Golgi is ever changing, why?

A

-flattened sacs of Golgi are constantly formed by fusion of vesicles from the rER
-these sacs then assemble into vesicles at the other side of the Golgi

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52
Q

What are somatic cells?

A

-body cells
-diploid (46 chromosomes)

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53
Q

How many chromosomes do gametes have?

A

23 (haploid)

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54
Q

What is the definition of meiosis?

A

-a ‘reduction’ division

-formation of haploid gametes from diploid cells
-two rounds of cell division: meiosis I and meiosis II

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55
Q
A

1- homologous chromosomes
2- non-sister chromatids
3- centromere
4- sister chromatids
5 - (mitiotic) chromosome

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56
Q

List the steps of meiosis I

A

-interphase 1 (before meiosis)

-prophase I
-prometaphase I
-metaphase I
-anaphase I
-telophase I

Cytokinesis

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57
Q

Name the steps of meiosis II

A

-prophase II
-prometaphase II
-metaphase II
-anaphase II
-telophase II
-cytokinesis II

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58
Q

What type of division is meiosis I?

A

-reduction

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59
Q

-what type of division is meiosis II?

A

-mitotic

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60
Q

What happens in interphase I?

A

-chromosomes duplicate

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61
Q

What happens in prophase I?

A

-chromosomes condense:
-they become visible as chromosomes consisting of two sister chromatids
-homologous chromosomes pair up (=synapsis) forming a bivalent (tetrad)
-crossing over of genetic material between homologous chromosomes occurs

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62
Q

What happens in prometaphase I?

A

-nuclear membrane breaks down
-spindle begins to form

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63
Q

What does crossing over formed?

A

Recombinant chromosomes

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64
Q

What is synapsis?

A

The process of homologous chromosomes pairing up

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65
Q

What is a bivalent (tetras)

A

-paired homologous chromosomes

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66
Q

What is the chisma?

A

-site of crossing over

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67
Q

What is crossing over?

A

-the exchange of genetic material between non sister chromatids of homologous chromosomes

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68
Q

What happens during metaphase I?

A

-chromsomes align as bivalents at equator of spindle (metaphase plate)
-independent assortment of chromsomes on the spindle allows for more genetic variation

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69
Q

What happens during anaphase I?

A

-spindle fibres contact, pulling homologous chromsomes to opposite poles of the cell

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70
Q

What happens during telophase I?

A

-chromsomes reach opposite poles of the cell and the nuclear membranes reform around each group of chromsomes

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71
Q

What happens during cytokinesis I

A

-a cleavage furrow forms and separates the two daughter cells

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72
Q

what happens during prophase and prometaphase II?

A

Prophase II:
-chromosomes are already condensed

Prometaphase II:
-nuclear membranes break down
-spindles begin to form

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73
Q

What happens during metaphase II?

A

-chromsomes align at metaphase plate

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74
Q

What happens during Anaphase II?

A

-spindle fibres contract, separating the 2 sister chromatids and pulling them to opposite poles of the cell

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75
Q

What happens during telophase II?

A

-nuclear membranes form around each set of chromatids
-chromsomes decondense (uncoil)

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76
Q

What are the results of meiosis?

A

4 haploid cells are formed (not genetically identical)

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77
Q

What is independent assortment?

A

Each new celll is a mixture of paternal and maternal chromosomes

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78
Q

What is the genetic variation due to random fertiliasaiton?

A

64 trillion combinations of zygotes

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79
Q

How does independent assortment of chromsomes in metaphase 1 lead to genetic variation?

A

-genes located on different chromsomes are unlinked and inherited independently (4 different gametes)

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80
Q

A dihybrid cross with 2 heterozygotes will have an expected ratio of:

A

9:3:3:1

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81
Q

What is gene linkage?

A

-Genes located on same chromsomes are linked and therefore not inherited independently (only 2 different gametes)

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82
Q

What happens when linked genes go through crossing over?

A

-a new combination of alleles and offspring with unexpected allele combinations (recombinant) ( 4 diff gametes)

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83
Q

What does the chance of two alleles being separated by crossing over depend on?

A

-their relative position on the chromsomes (their gene locus)
-the closer the genes are the less likely they will be separated by crossing over

84
Q

How are gametes made?

A

Meiosis

85
Q

Where are gametes made?

A

-testes and ovaries

86
Q

In men when do gametes form?

A
  • from puberty onwards
87
Q

In women when are gametes made?

A
  • eggs are developed in the fetus (at 14 weeks)
  • from puberty once a month an egg matures
  • arrest in metaphase 2
  • ovulation
  • completed upon fertilisation
88
Q

Describe the nucleus of a sperm

A
  • contains highly condensed haploid chromosomes
89
Q

What are the mitochondria like in a sperm cell?

A
  • tightly packed
  • provide ATP energy for movement of the tail
90
Q

What is the function of the flagellum?

A
  • to propel the sperm by its movement in a liquid environment
91
Q

What are microtubules?

A
  • responsible for movement of the tail (which keeps sperm in suspension and helps fit swim towards the egg)
92
Q

What is the acrosome?

A
  • membrane-bound storage site for enzymes
  • enzymes digest the layer surrounding the ovum and allow the sperms nucleus to enter egg
93
Q

What are the follicle cells of egg cells?

A
  • cells surrounding the ovum
  • release chemicals to trigger the acrosome reaction
94
Q

What are the lipid droplets in the egg cells for?

A
  • food store for developing embryo
95
Q

What is the function of the zona pellucida?

A
  • jelly-like layer made of glycoprotein
  • essential for binding of sperm and acrosome reaction
96
Q

Describe the nucleus of an egg cell

A
  • contains haploid genome
97
Q

What are cortical granules?

A
  • type of lysosome which releases enzymes to thicken the zona pellucida to prevent entry of other sperm after fertilisation
98
Q

Describe fertilisation.

A
  1. Sperm is attracted by a chemical released by the ovum
    - chemicals released by follicle cells trigger acrosome reaction
  2. Acrosome membrane fuses with front of the sperm cell membrane
    - digestive enzymes in acrosome are released
  3. Digestive enzymes digest the zona pellucida
  4. The sperm membrane fuses with the ovum membrane
  5. Sperm nucleus enters the ovum
  6. Cortical reaction: enzymes released from the ovum causes the zona pellucida to form a tough fertilisation membrane which prevents entry of other sperm nuclei
  7. The nuclei of the sperm and ovum fuse (the egg is now fertilised and a diploid zygote has formed)
99
Q

What is the function of the cell cycle?

A
  • producing identical daughters cells for growth and repair
  • and asexual reproduction
100
Q

Describe the G1 phase

A
  • main time of growth (new organelles)
  • high metabolic activity
  • high amount of protein synthesis
  • length varies (approx. 10h in rapidly dividing cells)
  • depends on growth factors: nutrient supply, temperature etc.
101
Q

What happens during the S phase and how long does it last?

A
  • DNA replication
  • DNA repair
  • centrosome duplication

Around 6hr

102
Q

Describe the G2 phase:

A
  • preparation for cell division
  • more growth
  • lasts 8hr
103
Q

What is the G0 phase>

A
  • cells may pause and enter a dormant state, in which they may stay temporarily or permanently (nerve cells)
104
Q

Describe the end of interphase:

A
  • dna is already de-condensed
  • chromosomes are replicated
  • centrosomes already duplicated
105
Q

What happens during prophase?

A
  • chromosomes condense and become visible
  • centrosomes separate and begins to form the mitotic spindle (microtubules)
106
Q

What happens during prometaphase?

A
  • nuclear envelope breaks down
  • chromosomes attach to spindle fibres via the kinetic horse
107
Q

What happens during metaphase?

A
  • chromsomes lines up at the metaphase plate
108
Q

Describe anaphase

A
  • the centromeres seperate and chromatids are pulled by spindle fibres towards opposite poles of cell
  • chromatids are now called chromosomes again
109
Q

What happens during telophase?

A
  • the chromosomes reach opposite poles of cell
  • the nuclear membranes reform
  • a cleavage furrow starts to form to divide the cytoplasm
110
Q

What happens during cytokinesis?

A
  • the chromsomes decondense
  • the nuclear membranes are fully reformed
  • the division of the cytoplasm and organelles continues until two new identical daughter cells are formed
111
Q

How does DNA content change during the cell cycle?

A
  • duplicates during S phase
  • halves during cytokineses
112
Q

What is the mitotic index formula?

A

Number of cells in mitosis / total number of cells

113
Q

Why might it be useful to calculate mitotic index?

A
  • its a measure of cellular proliferation
  • in cancer cells there may be an elevated mitotic index. Therefore it is an important prognostic factor in predicting overall survival and respond to chemotherapy in most types of cancer
114
Q

Why is mitosis important?

A
  • growth (more cells)
  • repair (replace cells)
  • asexual reproduction (new organisms)
115
Q

What ensures the genetic identity of daughter cells?

A
  • DNA replication prior to division
  • arrangement of chromsomes on spindle and separation of chromatids to the poles
116
Q

What is checked at the G1 checkpoint?

A
  • is the cell large enough?
  • is the environment suitable?
117
Q

What is checked at the G2 checkpoint?

A
  • has all the DNA replicated?
  • is there any DNA damage
  • is the environment suitable?
118
Q

What is checked at the M checkpoint?

A
  • are the chromosomes properly aligned?
119
Q

What is the cell cycle controlled by?

A
  • ENZYMES
  • cyclin-dependent kinases (CDK) a family of protein kinases
  • CDK proteins phosphorylate target proteins bringing about the next stage in the cell cycle
120
Q

If crossing over takes place two…

A
  • Linked genes can be homologous
  • this can lead to a new combination of alleles and offspring with unexpected allele combinations (=recombinant)
121
Q

How can the frequency of crossing over be calculated?

A
  • working out the % of recombinant offspring
  • can be used to draw chromosome maps
122
Q

How do you calculate crossover frequency?

A

of recombinant / total # of offspring x 100

123
Q

What is a chi-squared test?

A

= a statistical test to see if an observed distribution fits with a theoretical distribution

124
Q

What is a null hypothesis?

A
  • there is no significant difference between observed and expectected ratios
125
Q

What is an alternative hypothesis?

A
  • there is a difference between observed and expected ratios
126
Q

State the ideal sentence for the analysis of a chi-squared test:

A
  • because x^2 = ……….. > the critical value of ……… at p=….., the null hypothesis is ………….: therefore the genes are ………
127
Q

What is sex linkage?

A
  • genes that are on the sex chromsomes are described as sex linked
  • sex linked genes are inherited with sex chromosomes
128
Q

Stem cells are cells that can:

A
  • replicate themselves
  • differentiate into other cell types
129
Q

What type of cells very early embryonic stem cells?

A
  • totipotent stem cells

(Zygote -> morula)

130
Q

What type of cells are embryonic stem cells?

A
  • pluripotent
    (Blastocyst)
131
Q

What type of cells are umbilical cord and adult stem cells?

A
  • multipotent stem cells
132
Q

What are totipotent stem cells?

A

Stem cells that can give rise to any cell type

133
Q

What are pluripotent stem cells?

A
  • stem cells that can give rise to most cell types
134
Q

What is a blastocyst?

A
  • hollow ball of ~200 cells
135
Q
A
  1. Blastocyst
  2. Outer cell mass (pluripotent)
  3. Cavity
  4. Outer cell mass (unipotent)
  5. Embryo
  6. Placenta
  7. Any cell type (not placental)
136
Q

What are multipotent cells?

A
  • cells that can give rise to only a few types of cells depending on the body tissue
137
Q

What is the source of multipotent stem cells:

A
  • adult stem fells and umbilical chord stem cells
138
Q

What do bone marrow stem cells differentiate into?

A
  • different types of blood cells v
139
Q

What is potency?

A
  • a cells ability to differentiate into other cell types
140
Q

What are embryonic stem cells?

A
  • pluripotent stem cells derived from the inner cell mass of a blastocyst
141
Q

What are adult stem cells?

A
  • Multipotent stem cells found in various tissue and organs
142
Q

A very small number of specialised cells in animals are…

A

Unipotent

143
Q

Differentiation in animals is mostly…

A

Irreversible

144
Q

Most stem cells in plants are…

A
  • totipotent (even when specialised)
145
Q

Differentiation in plants is…

A

Reversible

146
Q

What are unipotent stem cells?

A
  • (some) specialised cells that can undergo mitosis, e.g T cells and liver cells
147
Q

How can totipotency in plants be demonstrated?

A
  • by micropropogation
  • single cells or explants can go on to produce adult plants
148
Q

What is micropropogation?

A

= plant cell tissue culture

149
Q

Describe micropropogation

A
  • explants (small pieces of plant) are placed into water and then into a medium containing nutrients and growth regulators in medium
  • a callus is formed and a new altered medium leads to differentiation that forms a plantlet
150
Q

Why is stem cell research controversial topic?

A
  • destruction of embryos
  • cloning
151
Q

What is another name for adult stem cells?

A
  • somatic stem cells
152
Q

What are the advantages of using embryonic stem cells for research?

A
  • pluripotent
  • can be obtained from IVF
153
Q

What’s are the disadvantages of using embryonic stem cells for stem cell research?

A
  • tissue rejection
  • destruction of embryos
154
Q

What are the advantages to using adult stem cells for stem cell research

A
  • no risk of rejection
  • no embryos destroyed
155
Q

What are disadvantages to using adult stem cells for stem cell research?

A
  • only multipotent
  • rare: harder to work with
156
Q

What is SCNT?

A
  • transfer of nuclear DNA from a somatic cell into an enucleated oocyte
  • fusion of nucleus and egg cell through a mild electric shock
  • cloned cell induced to form embryo forming a blastocyst
157
Q

Why does using SCNT remove the problem of rejection?

A
  • stem cells are genetically identical to the somatic cell that donated the DNA
158
Q

What is the biggest hurdle to human SCNT?

A
  • scarcity of human oocytes which are donated from IVF
159
Q

What is another limitation to SCNT and IPSC?

A
  • they can retain epigentic memory of the somatic cell used to derive them
  • leading to limitations in cell types that are produced following differentiation
160
Q

What are the disadvantages of SCNT embryonic stem cells

A
  • destruction of embryos
  • could lead to reproductive cloning of humans
161
Q

What are induced pluripotent cells?

A
  • when adult stem cells are genetically reprogrammed to be pluripotent stem cells
162
Q

What are the disadvantedges associated with induced pluripotent adult stem cells?

A
  • risks associated with genetic reprogramming
163
Q

What are the scientific developments associated with hPSCS?

A
  • patient specific PSCs used for drug testing and disease modelling
  • hPSCs have been used to make organoids of liver, stomach and heart
  • culturing tissues to make organoids give scientists a detailed view of how organs and embryos form and is likely to revolutionise drugs discovery and personalised medicine
164
Q

Describe ethics in stem cell research

A
  • governing bodies have no ethical objections to using multipotent stem cells derived from adult cells
  • development of iPSC led some people to suggest that this solves ethical concerns of ESCs
  • debate between similarity of ESC and iPSC
  • in the UK HFEA regulates resarch on human embryos
165
Q

All cells in a multicellular organism contain..

A

The same genetic information (except for mutations)

166
Q

What is acetabularia

A
  • green algae
  • single cell
167
Q

What controls the development of the whole cell?

A
  • the nucleus
168
Q

Describe how development is controlled in the acetabularia

A
  • a chemical messenger in the stem has influenced hat development
  • the nucleus hat also influenced hat development
  • over time the chemical messenger in stem disappears
  • now cell development is completely controlled by the nucleus
169
Q

What is differential gene expression?

A

= different specialised cells express different genes (and in different amounts)

170
Q

Describe the process of stem cells to different cell types

A
  • stems cells + stimulus
  • different genes turned on and transcribed
  • different proteins made
  • different cell types
171
Q

What stimulates differential gene expression?

A
  • internal stimuli
  • external stimuli
  • temporal cues
  • spatial cues
172
Q

Describe how the blastula and grastula turns into free CDNA which is hydrolysed

A
  1. mRNA from blastula + gastrula isolated
  2. CDNA made using reverse transcriptase (grastula side)
  3. mRNA digested leaving only cDNA (grastula side)
  4. MRNA from blastula and cDNA from grastula: complementary strands hybridise
  5. Free CDNA analysed
173
Q

Why are there many checks during gene expression?

A
  • so that the correct proteins are synthesised in the correct amounts when needed
174
Q

What is the type of control between DNA and RNA transcript?

A
  • transcriptional control
175
Q

What is the type of control between RNA transcript and mRNA?

A
  • rna processing control
176
Q

What is the control between mRNA in the nucleus and mRNA outside the nucleus

A
  • mRNA transport and location control
177
Q

What is the control between mRNA and inactive mRNA?

A
  • mRNA degradation control
178
Q

What is the control between mRNA and protein

A
  • translation control
179
Q

What is the control between protein and inactive protein?

A
  • proteins activity contorl
180
Q

How is DNA structured in eukaryotes?

A
  • DNa is wrapped around histone proteins forming nucleosomes
181
Q

What happens when nucleosomes are tightly packed together?

A
  • RNA polymerase and other transcription factors cannot bind to the DNA
182
Q

How do you relax chromsome packing to make genes accessible for transcription?

A
  • via chromosmes remodelling complexes or histone modification
183
Q

What a chromosome remodelling complexes?

A
  • protein complexes that create nucleosome-free regions of DNA for gene activation by RNA polymerase
184
Q

How do chromsomes remodelling complexes work?

A
  • by removing histones or moving them along the DNA (nucleosome sliding)
185
Q

How else can histones be modified using chemicals?

A
  • modification of histones via binding of chemical markers such as methyl acetate
  • or phosphate groups to histones tails affects wrapping of dna around histones
186
Q

Histones modification can expose…

A

DNA so that’s rna polymerase and other transcription factors can attach

187
Q

What is the definition of histones modification?

A
  • binding of methyl groups to histone tails alters how tightly dna winds around histone proteins
188
Q

What makes up the epigenome?

A
  • histone modification together with modification of the DNA itself
189
Q

Attachment of methyl groups to dna of a gene prevents…

A

Transcription by stopping rna polymerase from binding

190
Q

For gene expression to happen the DNA must not be:

A
  • methylated
  • histones should be modified so that the DNA is slightly uncoiled
191
Q

Only genes in ………………………. Regions of eukaryotic dna can be transcribed into mRNA

A

Uncoiled

192
Q

What are transcription depressors?

A
  • transcription cannot occur when a repressor proton binds to the promotor region
  • the repressor stops rna polymerase from binding
  • when repressor is removed transcription can proceed
193
Q

What are transcriptional activators?

A
  • in some instances transcription cannot occur without an activator protein being bound to the promotor
194
Q

How is transcription carefully controlled?

A
  • promotor and adjoining regulatory sequences of DNA Upstream of gene bind with rna polymerase, transcription factors, activators and repressor
195
Q

What is mRNA digested by?

A
  • RNAase enzymes
196
Q

Repressor proteins do not always completely inhabit transcription but may…

A
  • instead reduce the number of mRNA molecules transcribed
197
Q

Bacteria do not have…

A
  • histones
  • therefore chromsomes remodelling and epigentic material is not involved in control of transcription
198
Q

Between the bacterial promoter and gene there is a dna sequence called an…

A

Operator

199
Q

What is the purpose of an operator in bacterial DNA?

A
  • repressor protein can bind and stop transcription by blocking rna polymerase
  • this system of promoter, operator and gene is called an operon
200
Q

What happens in E Coli when lactose is not present?

A
  • lactose repressor binds to operators and stops B galactosidase gene being expressed (by stopping rna polymerase from binding to promotor)
201
Q

What happens if there is glucose present?

A
  • activator absent (wasteful)
202
Q

What happens if no lactose is present?

A
  • repressor present
203
Q

What happens if lactose is present?

A
  • it binds to the repressor, repressor is prevented from binding to dna and b galactosidase is expressed v
204
Q

What happens when glucose is absent

A
  • activator protein binds to DNA
205
Q

What is required for b galactosidase to be produced?

A
  • presence of an activator(no glucose) and removal of the repressor (lactose present)
206
Q

What is sued to test for b galactosidase activity?

A
  • ONPG as it is structurally similar to lactose and broken down by B.G
  • colourless -> yellow
207
Q

What has a higher oxygen affinity fetal or adult haemoglobin?

A
  • fetal
  • changes during development
  • levels change in different tissues at different times

Biology (6 decks)

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