Unit 2- Human Cells Flashcards
What are somatic cells?
Any body cells other than those involved in reproduction (sex cells and sex stem cells)
How do somatic cells divide?
By mitosis to form more somatic cells
What are germline cells?
Gametes and the stem cells that divide to form them
How do germline cells divide?
By mitosis to form more germline cells then by meiosis to form haploid sex cells
Why do germline cells divide by mitosis?
To maintain the diploid chromosome complement
What are the stages of meiosis?
1) The chromosomes in the cell are copied
2) Homologous chromosomes pair up along the equator
3) One from each pair move to opposite sides of the cell leading to 2 daughter cells being produced
4) Each daughter cell divides again by separating the chromatids to form 4 sex cells. These cells are haploid containing only 23 chromosomes not pairs.
What is cellular differentiation?
The process by which a cell develops more specialised functions by selective gene expression.
What is selective gene expression?
When only a fraction of the genes are left switched on so only those are expressed producing the specific proteins for a characteristic.
What are stem cells?
Undifferentiated somatic cells that can divide to either make copies of themselves or differentiate into specialised cells.
What are the 2 types of stem cells?
Embryonic and tissue(adult)
Where are embryonic stem cells come from?
Very early embryos
Are embryonic stem cells multipotent or pluripotent and why?
Pluripotent because all of the genes have the potential to be switched on so the cells can differentiate into any cell type.
Where do tissue stem cells come from?
Tissue and bone marrow.
Are tissue stem cells multipotent or pluripotent and why?
Multipotent because many of their genes are already switched off so can only differentiate into a limited number of cells. Cells closely related to the tissue they were found in.
What are the therapeutic use for stem cells?
Regeneration of damaged tissue
Corneal repairs
Embryonic stem cells can self renew under the right conditions in the lab
What are the research used of stem cells?
Model cells to study how diseases develop or drug testing
Look at cell processes such as, cell growth, differentiation or gene regulation
What are the type ethical issues with embryonic stem cells?
They can offer effective treatments for diseases but involves the destruction of embryos
What is the difference between a cancer cell and a regular cell?
Cancer cells don’t respond to regulatory signals and divide excessively
What is a mass of cancer cells called?
A tumour
How are secondary tumours formed?
The cells on the primary tumour lose they’re surface molecules that keep them attached to the original tumour and they travel through the circulatory system and seed into other tissues.
What does one DNA nucleotide consist of?
A deoxyribose sugar, a phosphate and a base
What does DNA stand for?
Deoxyribonucleic acid
What does DNA consist of?
2 strands of repeating units called nucleotides
How is the sugar-phosphate back bone formed?
Strong chemical bonds form between the phosphate group of one nucleotide and the deoxyribose sugar of the next
What are the 4 bases of DNA and their complementary pairs?
Adenine——Thymine
Cytosine——Guanine
What is meant by DNA having an antiparallel structure?
The 2 strands run in opposing directions with one end bearing the deoxyribose 3’ end and the other the phosphate 5’end
What name is given to the structure of DNA?
Double helix
What joins bases together?
Weak hydrogen bonds
What are the requirements for DNA replication?
DNA Primers Supply of nucleotides Enzymes (ligase and DNA polymerase) ATP
What are the steps of DNA replication?
- DNA unwinds and hydrogen bonds break between bases to form 2 template strands
- primers bind to the 3’ end to start replication
- DNA polymerase adds new complementary nucleotides to the template strands from the primer onwards.
- the leading strand is replicated continuously
- the lagging strand is replicated in fragments with many primers and ligase joining the fragments together
What are primers?
Short strands of nucleotides that are 5’
What direction does DNA replication happen?
3’to 5’ on the parent strand
What is PCR?
A process that amplifies small quantities of DNA using complementary primers which are complementary to the specific target sequence.
What are the requirements for PCR?
Heat tolerant DNA polymerase
Primers
Free nucleotides to make amplified DNA
Original DNA strand needed to be replicated
Enzymes
What temperature is DNA heated to to separate the strands and break the hydrogen bonds in PCR?
92-98 degrees
What does cooling the DNA to 50-65 degrees allow?
It allows the primers to bind to the target sequences
what does heating DNA back up to 70-80 degrees allow?
It allows heat tolerant DNA polymerase to replicate the region of DNA
What are the uses of PCR?
Help solve crimes
Settle paternity suits
Diagnose genetic disorders
What is gene expression?
the transcription and translation of DNA expressing only a fraction of the genes in a cell
Describe the differences between DNA and RNA
RNA- single stranded
contains uracil (u)
has a ribose sugar
DNA- double stranded
contains thymine
contains deoxyribose sugar
what are the three types of RNA?
mRNA
rRNA
tRNA
What is the role of mRNA?
To carry a copy of the DNA code from the nucleus to the ribosome.
what is the role of tRNA?
to carry specific amino acids to the ribosome
What is the role of rRNA?
To form the ribosome with proteins
Describe the structure of mRNA
a series of base triplets known as codons which code for a specific amino acid.
Describe the structure of tRNA
folded due to complementary base pairing
an exposed triplet of bases on one side known as an anticodon
and carries a specific amino acid on the opposite side
What is transcription?
the synthesis of mRNA from a section of DNA
Describe the process of transcription
RNA polymerase moves along the DNA strand unwinding and breaking hydrogen bonds between bases
RNA polymerase adds new complementary RNA nucleotides
this breaks off and is the primary transcript
the RNA is then spliced: introns(non coding regions) are removed and exons(coding regions) are joined together
this produces the mature transcript.
What is translation?
the synthesis of a polypeptide from mRNA at the ribosome
describe the process of translation
the mRNA travels out of the nucleus to the ribosome
translation begins at a start codon and ends at stop codon.
Each tRNA picks up its specific amino acid
Each anticodon on the tRNA is complementary to a codon on the mRNA and bonds by complementary base pairing, translating genetic code into a sequence of amino acids
peptide bonds join the amino acids on the tRNA and the tRNA molecule leaves to carry more amino acids.
what is a polypeptide?
a chain of amino acids joined by peptide bonds
what is alternative RNA splicing?
different segments of RNA can be treated as exons and introns meaning one primary transcript can produce several mature transcripts
how are proteins formed from polypeptides?
the polypeptides fold to form a 3D shape held together by hydrogen bonds and interactions between individual amino acids
What is a mutation?
a change in the DNA that can result in no protein or an altered protein being synthesised.
What are the two types of mutation?
single gene mutations
chromosome structure mutations
What are the types of single gene mutation?
substitution
insertion
deletion
what are the types of chromosome structure mutations?
deletion
duplication
translocation
inversion
what is the definition of a deletion chromosome mutation?
a section of the chromosome is removed and the rest is rejoined
what is the definition of a duplication chromosome mutation?
a section of a chromosome is added from its homologous partner.
what is the definition of a translocation chromosome mutation?
a section of chromosome is added from its non homologous partner
what is the definition of an inversion chromosome mutation?
a section of chromosome is reversed and rejoined
what is a single gene mutation?
the alteration of a DNA nucleotide sequence due to substitution, insertion, or deletion of nucleotides
what 3 things can nucleotide substitution mutations result in?
missense mutations
nonsense mutations
splice site mutations
what is a missence mutation?
a substitution that results in one amino acid being changed for another resulting in either a non-functional protein or very little effect on the protein
what is a nonsense mutation?
a substitution mutation resulting in a premature stop codon being produced resulting in a shortened protein
what is a splice-site mutation?
a substitution mutation resulting in some introns being retained and/or some exons not being included in the mature transcript
what is a nucleotide insertion mutation?
the insertion of an extra nucleotide in the DNA sequence resulting in a frame shift
what is a nucleotide deletion mutation?
the deletion of a nucleotide in the DNA sequence resulting in a frame shift
what does frame shift mean?
everything is moved so all amino after mutation is changed having a major effect on the structure of the proteins produced
what is the genome of an organism?
its entire hereditary information encoded in DNA, the genes and other areas of DNA that do not code for proteins
what is genomic sequencing?
when the sequence of nucleotide bases for individual genes and entire genomes is determined
how does genomic sequencing work?
computer programmes can be used to identify base sequences by looking for sequences similar to known genes
what is bioinformatics?
the use of computers and statistical technology to identify DNA samples
what is a positive use for genomic sequencing?
to predict the likelihood of developing certain diseases.
what is pharmacogenetics?
the use of genome information in the choosing the most effective drugs and dosage to treat an individuals disease
What is a metabolic pathway?
a series of enzyme controlled steps
what is an anabolic pathway?
the synthesis of larger molecules from smaller ones
do anabolic pathways require energy?
yes
what is a catabolic pathway?
the breakdown of larger molecules to smaller ones
do catabolic pathways require energy?
no they release energy
what are the two types of metabolic pathway?
anabolic
catabolic
what is cell metabolism?
a collective term for thousands of biochemical reactions that occur in a living cell
what is required for a metabolic pathway to proceed?
specific enzymes for each step in the pathway
how is enzyme action controlled?
by the presence or absence of particular enzymes
how is enzyme action regulated?
the rate of reaction of key enzymes
how are wasted resources prevented in metabolic pathways?
by ‘switching on/off’ genes that code for the enzymes for each stage as they are required rather than all of the time
what is activation energy?
the energy required for reactants to reach a transition state
how to enzymes speed up chemical reactions?
by lowering the activation energy
what is the transition stage in a chemical reaction?
the state at which the reactants have absorbed enough energy to make them unstable allowing the reaction to happen
describe the process of an enzyme controlling a chemical reaction
the enzymes active site has a high affinity to the substrate molecules
when the two combine the reactants are orientated to the active site
the activation energy is lowered
the products, which have a low affinity to the active site, are released
what is meant by induced fit?
the active sites of enzymes are not rigid in shape as when the substrate molecule enters the active site, it changes slightly making it fit the substrate molecule more closely
what is the effect of substrate concentration on enzyme activity?
at low concentrations of substrate:
reaction rate is low due to too few molecules to make full use of active sites
an increase in substrate:
increase in reaction rate as more active sites are in use
further increase in substrate concentration:
no more effect on reaction rate as all the active sites are already in use
what do inhibitors do in metabolic pathways?
control metabolic pathways by decreasing the rate of enzyme action
what are the two types of inhibitors?
competitive
non-competitive
describe competitive inhibitors
competitive inhibitors bind to the active site preventing the substrate from binding
but
can be overcome by increasing the substrate concentration as there is then a higher chance of enzyme-substrate interaction
describe non-competitive inhibitors
non-competitive inhibitors become attached to a non-active site causing a change in the shape of the active site
these cannot be reversed by increasing substrate concentration
what is feedback inhibition?
feedback inhibition is when the concentration of end product builds up and reaches critical concentration, inhibiting an earlier enzyme, blocking the pathway and so prevents further synthesis of end products
in what order does cellular respiration occur?
glycolysis
citric acid cycle
electron transport chain
what is phosphorylation?
when a phosphate group is added to a molecule
in summary what is glycolysis?
the breakdown of glucose to pyruvate
where does glycolysis occur?
the cytoplasm of the cell
does glycolysis require oxygen?
yes
what are the two stages of glycolysis?
energy investment stage
energy payoff stage
describe the whole of the energy investment stage of glycolysis
ATP is required
ATP is broken down into ADP and a Pi group
this is used in the phosphorylation of intermediates
describe the whole process of the energy payoff stage of glycolysis
ATP is produced
ATP is directly generated so there is a net gain pf 2 ATP
describe the link reaction between glycolysis and the electron transport chain
if oxygen is present pyruvate is broken down into an acetyl group.
the acetyl group then combines with coenzyme A to form acetyl coenzyme A
where does the citric acid cycle occur?
the matrix of the mitochondria
does the citric acid cycle occur with or without oxygen?
with oxygen
describe the citric acid cycle
the acetyl group from the acetyl coenzyme combines with oxaloacetate to form citrate
during a series of enzyme controlled steps, citrate is gradually converted back into oxaloacetate
this generates ATP and releases carbon dioxide
Describe the role of dehydrogenase enzymes
remove hydrogen ions and electrons from both glycolysis and the citric acid cycle and passes then to the coenzyme NAD to form NADH
these hydrogen ions and electrons are passed to the electron transport chain
what actually is the electron transport chain?
a series of carrier proteins attached to the inner mitochondrial membrane.
describe the electron transport chain
NADH releases its h+ ions and electrons to the chain where they cascade down the chain, releasing energy.
this energy is used to pump h+ ions across the inner mitochondrial membrane by active transport
return flow of h+ ions drives ATP synthase (rotates) and produces the bulk of ATP
the final electron acceptor is oxygen which combines with h+ ions and electrons to form water
what is ATP?
high energy compound which transfers energy
How is ATP formed?
when ADP combines with a phosphate group (phosphorylation)
How does ATP release energy?
when ATP is broken down into ADP and a Phosphate group
What is lactate metabolism?
when during vigorous exercise, muscles don’t get enough oxygen to support the electron transport chain , so pyruvate is converted into lactate instead of following the normal pathway.
How does lactate metabolism work?
the hydrogen from NADH is transferred to pyruvate to produce lactate which regenerates the NAD required to produce ATP in glycolysis.
Describe how oxygen debt is made and repaid during lactate metabolism
As lactate builds up in muscles, muscle fatigue occurs and an oxygen debt is built up.
when exercise stops the oxygen debt is repaid allowing respiration to provide the energy required to convert lactate back to pyruvate.
What are the 2 types of skeletal muscle fibres?
Slow twitch and fast twitch
what are the properties of slow twitch muscle fibres?
contract slowly but can sustain contractions for a long time
rely on ATP from aerobic respiration.
have many mitochondria
have a large blood supply
have a high concentration of myoglobin
major storage fuel is fats
what are the properties of fast twitch muscle fibres?
contract more quickly but only maintain contractions for a short period of time
rely on ATP from glycolysis
have few mitochondria
have a lower blood supply
have a lower concentration of myoglobin
major storage fuel is glycogen
what types of activities are slow twitch muscle fibres best equipped for?
endurance activities such as long distance running or cycling
what type of activities are fast twitch muscle fibres best equipped for?
short bursts of activity such as weightlifting or sprinting
what is myoglobin?
the protein that stores oxygen in muscles
