Human Cells Flashcards
What is a somatic cell?
Any body cell other than those involved in reproduction
How do somatic cells divide?
Mitosis
What are germline cells?
Gametes and the stem cells that divide to form gametes
How do germline cells divide?
By mitosis and meiosis
Does mitosis maintain the diploid chromosome complement?
Yes
How many homologous pairs are made in mitosis?
23
What does meiosis produce?
Haploid gametes
What are the two divisions that happen during meiosis?
1 - separating homologous chromosomes
2 - separating chromatids producing 23 single chromosomes in each haploid cell
How many daughter cells does mitosis produce?
2
How many daughter cells does meiosis produce?
4
What is cellular differentiation?
The process by which a cell develops more specialised functions by selective gene expression
How does cellular differentiation work?
Only a fraction of the genes remain switched on so only those are expressed producing the characteristics specific proteins
What are stem cells?
Undifferentiated somatic cells
What do stem cells divide to do?
Make copies of themselves
Differentiate into specialised cells
Where are embryonic stem cells found?
A very early embryo
What are the genes like in an embryonic stem cell?
All of the genes have the potential to be switched on so they can differentiate into almost any cell type
What are embryonic stem cells known as?
Pluripotent
Where are tissue stem cells found?
In tissue and bone marrow
What are the genes like in tissue stem cells?
Many of the genes are already switched off so they can only differentiate into a limited number of cells (closely related to the tissue they are found in)
What can bone marrow differentiate into?
Different blood cells
What are tissue stem cells known as?
Multipotent
What are tissue stem cells involved in?
The growth, repair and renewal of cells found in that tissue
What do germline cells produce when they divide by meiosis?
Gametes
What do germline cells produce when they divide by mitosis?
Copies of themselves
What are the 2 therapeutic uses of stem cells?
Regeneration of damaged tissue
Corneal repairs
When can stem cells renew?
Under the right conditions in the lab
What are the 3 research uses of stem cells?
Model cells to study how diseases develop
For drug testing
They provide information on how cell processes such as cell growth, differentiation and gene regulation work
What are the ethical issues of stem cells?
They offer effective treatments for disease and injury, however it involves the destruction of embryos
Why do cancer cells divide excessively?
They don’t respond to regulatory signals - this results in a mass of abnormal/cancer cells known as a tumour
What happens if cells within the rumour fail to attach to each other?
They can spread throughout the body and form a secondary tumour
What does DNA stand for?
Deoxyribose nucleic acid
What are the two strands of repeating units in DNA called?
Nucleotides
What are nucleotides composed of?
Deoxyribose sugar
Phosphate
A base
What does a chemical bond form between?
The phosphate group of one nucleotide and the deoxyribose of another forming a sugar - phosphate backbone
What type of bonds join the bases on each strand if nucleotides to form base pairs?
Weak hydrogen bonds
What does the base sequence form?
The organisms genetic code
What structure does DNA have and what does this mean?
Anti-parallel
This means the 2 strands run in opposite directions with one end bearing the deoxyribose 3’ end and the other the phosphate 5’ end
What is the shape of DNA known as?
A double helix
When does DNA replication occur?
Before cell division
What does DNA replication begin with?
DNA unwinding
What is DNA replicated by?
A DNA polymerase
What 5 things are required for DNA replication?
DNA template Primers Nucleotides Enzymes ATP
What are primers?
Short strand of nucleotides which binds to 3’ end
What enzymes are used in DNA replication?
DNA polymerase and sometimes ligase
What is the process of DNA replication?
DNA unwinds
Hydrogen bonds break between
bases to form 2 template strands
Primer bonds to 3’ end to start replication
DNA polymerase adds new complementary nucleotides to the template strands from the primer onwards
What direction does replication occur?
3’ to 5’
What happens to the leading strand during DNA replication?
It is replicated continuously
What happens to the lagging strand during DNA replication?
New nucleotides can only be added to the 3’ end so it is replicated in fragments with many primers
Fragments are joined together by ligase
What happens in PCR?
DNA is amplified using complementary primers which are complementary to a specific target sequence at two ends of the region of DNA
How is the target region amplified during PCR?
By repeated cycles of cooling and heating
What happens when DNA is heated to 92-98°C in PCR?
Hydrogen bonds break and strands separate
What happens when mixture is cooled to 50-65°C in PCR?
Allows primers to bind to target sequences
What happens when mixture is heated between 70-80°C in PCR?
Heat tolerant polymerase replicates region of DNA
What is PCR used for?
Forensics to help solve crimes
Settle paternity suits
Diagnose genetic disorders
What does gene expression involve?
Transcription and translation of DNA expressing only a fraction of the genes in a cell
Describe RNA
Single stranded
Has uracil instead of thymine
Has ribose sugar instead of deoxyribose sugar
What are the 3 types of RNA?
mRNA
tRNA
rRNA
What is mRNA (messenger RNA) and what does it do?
mRNA is made of a series of base triplets known as codons
It carries a copy of the DNA code from the nucleus to ribosome
What does a codon do?
Codes for a specific amino acid
What is tRNA (transfer RNA) and what does it do?
Carries a specific amino acid to the ribosome
Folds due to complementary base pairing
Has an exposed triplet of bases known as an anticodon at one end
Has an attachment site for a specific amino acid at the other end
What is rRNA (ribosomal RNA) and what does it do?
Forms the ribosome with proteins
What is transcription?
The synthesis of mRNA from a section of DNA
What happens in transcription?
RNA polymerase moves along the DNA strand unwinding and breaking the hydrogen bonds between the bases, adding new RNA nucleotides following RNA base pairing rules
RNA polymerase can only add new nucleotides to the 3’ end of the new mRNA strand
The resultant mRNA breaks off and is the primary transcript
What happens during RNA splicing?
Regions of the transcript (in transcription) are known as introns and exons
Introns are cut out and exons joined together
Now known as the mature transcript
What is translation?
The synthesis of a polypeptide from mRNA at the ribosome.
What happens during translation?
Ribosome attaches to mRNA
Ribosome reads start codon to start translation
As ribosome reads each codon, complementary tRNA with anticodon and amino acid attached binds to codon
When the next codon is read and anticodon attaches, peptide bond forms between the two amino acids
tRNA molecule detaches from amino acid and leaves to pick up another
What is the difference between introns and exons?
Introns are non-coding
Exons are coding
What is alternative RNA splicing?
Different segments of mRNA may be treated as exons and introns
The same primary transcript can produce several mature transcripts
What is a polypeptide?
Amino acids linked by peptide bonds
What happens to polypeptides?
They fold to form a 3D shape held together by hydrogen bonds and interactions between individual amino acids
What does the protein shape determine?
Their function
What is the phenotype of a gene determined by?
The protein produced as a result of gene expression which can be influenced by environmental factors
What is a mutation?
Change in the DNA that can result in no protein or an altered protein being synthesised
What are the 3 types of single gene mutations?
Substitution
Insertion
Deletion
What does a substitution mutation result in?
Missense mutations
Nonsense mutations
Splice-site mutations
What is a missense mutation?
One amino acid being changed for another
Results in either a non-functional protein or very little effect on the protein
What is a nonsense mutation?
A premature stop codon being produced
Resulting in a shortened protein
What is a splice-site mutation?
Some introns being retained and/or some exons not being included in the mature transcript
What does an insertion/deletion result in?
A frame-shift mutation
What is a frame-shift mutation?
Everything is moved so all amino acids after mutation is changed
This has a major effect on the structure of the protein produced
What is the genome of an organism?
It’s entire hereditary information encoded in DNA
What is a genome made up of?
Genes and other DNA sequences that do not code for proteins
What can be determined in genomic sequencing?
The sequence of nucleotide bases for individual genes and entire genomes
What is used to identify base sequences in genomics and how?
Computer programmes by looking for sequences similar to known genes
What is bioinformatics?
The use of computer and statistical technology to identify DNA samples
What is pharmacogenetics?
The use of genome information in the choice of drugs
Why may an individuals genome be analysed?
To predict the likelihood of developing certain diseases
What can an individuals personal genome sequence be used to do?
Select the most effective drugs and dosage to treat their disease - known as personalised medicine
What is a metabolic pathway?
When one chemical is changed to another, then to another via a series of enzyme controlled steps
What is an anabolic pathway and is energy required?
The synthesis of larger molecules from smaller ones
Energy is required
What is a catabolic pathway and is energy required?
Breakdown of larger molecules down to smaller ones
Energy is released
What can the steps in metabolic pathways be?
Reversible or irreversible
When do alternative routes occur in metabolic pathways?
When there is a plentiful supply of one metabolite in a pathway
How are metabolic pathways controlled?
Each step is driven by a particular enzyme, and a particular gene codes for each enzyme, so as long as the enzyme proteins are correctly functioned, the pathway proceeds
What is enzyme action controlled by and regulated by?
Controlled by - The presence or absence of particular enzymes
Regulated by - The rate of reaction of key enzymes
What do enzymes do?
Speed up chemical reactions by lowering the activation energy required for the reactants to reach the transition state
What are the active sites of enzymes like?
They have a high affinity for substrate molecules and when the two combine, the reactants are orientated to the active site, the activation energy is lowered and the products and released
Do the products have a higher or lower affinity for the active site?
Lower
What is induced fit?
The active site is not a rigid structure as when the substrate enters the active site, it changes slightly, making it fit the substrate molecule snugly
What happens as the substrate concentration increases?
At low concentrations - reaction rate is low due to too few substrate molecules to make full use of all active sites
An increase - increase in reaction rate as more of the active sites are in use
Further increase - no more effect on reaction rate as all the active sites are in use
In reversible reactions, what can the presence of substrate do?
Drive the direction of the reaction
What do inhibitors do?
Control metabolic pathways by decreasing the rate of enzyme action
What do competitive inhibitors do?
Bind to the active site preventing the substrate from binding
This can be overcome by increasing the substrate concentration as there are then a higher chance of enzyme-substrate interaction
What do non-competitive inhibitors do?
Become attached to a non-active site causing a change in shape of active site and cannot be reversed by increasing substrate concentration
What is feedback inhibition?
It happens as the concentration of end product builds up and reaches critical concentration, it inhibits an earlier enzyme, blocking the pathway and so prevents further synthesis of the end product
What are the 3 stages of cellular respiration?
Glycolysis
Citric acid cycle
Electron transport chain
What is a duplication mutation?
A section of a chromosome is added from its homologous partner
What is a deletion mutation?
Where a section of chromosome is removed and rest rejoined if needed
What is an inversion mutation?
A section of chromosome is reversed
What is a translocation mutation?
A section of a chromosome is added to a chromosome which is not its homologous partner
What do substantial changes in chromosome structure do?
Make them lethal
What are the 4 types of chromosome structure mutation?
Duplication
Deletion
Inversion
Translocation
What happens during glycolysis?
It is a series of enzyme controlled reactions in two stages
Occurs in cytoplasm
Glucose is broken down into pyruvate
Energy investment stage -
ATP required, phosphorylation of glucose and the intermediated
Energy payoff stage -
Involves the direct generation of ATP
Results in a net gain of ATP
What happens during the citric acid cycle?
Oxygen is required
Pyruvate is broken down to an acetyl group and combines with coenzyme A to produce acetyl coenzyme A
Occurs in the matrix of the mitochondria
The acetyl group from acetyl coenzyme A combines with oxaloacetate to form citrate
During a series of enzyme controlled steps, citrate is gradually converted back into oxaloacetate
The cycle generates ATP and releases carbon dioxide
Dehydrogenaze enzymes remove hydrogen ions and electrons from both glycolysis and citric acid cycle and passes them to the coenzyme NAD forming NADH
The hydrogen ions and electrons from NADH are passed to the electron transport chain
What happens in the electron transport chain?
The electron transport chain is a series of carrier proteins attached to the inner mitochondrial membrane
The NADH passed its hydrogen ions and electrons down a series of electron acceptors, releasing their energy, which is used to pump hydrogen ions across the inner membrane by active transport
The return flow of hydrogen ions by diffusion via the membrane protein, ATP synthase, drives the synthesis of the bulk of ATP produced in respiration
The final electron acceptor is oxygen, which combines with hydrogen ions and the electrons to form water
What is ATP?
The high energy compound which transfers energy
When is ATP produced?
when ADP combines with phosphate in phosphorylation building up energy
What is ATP broken down into?
ADP and phosphate with energy being released
What happens in lactate metabolism?
During vigorous exercise, muscled do not get sufficient oxygen to support the electron transport chain so pyruvate is converted into lactate instead of following the normal pathway.
The hydrogen from the NADH produced in glycolysis is transferred to pyruvate in order to produce lactate, regenerating the NAD needed to maintain ATP production during glycolysis.
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 needed to convert lactate back to pyruvate and glucose in the liver.
What is pyruvate concerted into during vigorous exercise/lactate metabolism?
Lactate
What happens as lactate builds up in muscles?
Muscle fatigue occurs and an oxygen debt is built up
What are the two types of muscle fibres that make up skeletal muscles?
Fast twitch
Slow twitch
Where do slow twitch rely on ATP from?
Respiration
Describe slow twitch muscle fibres
Contract relatively slow but can sustain the contractions for a long time
Have many mitochondria
Have a large blood supply
Have a high concentration of myoglobin
Major storage fuel is fats
What are slow twitch fibres good for?
Endurance activities such as long distance running or cycling
What does fast twitch rely on for ATP?
Glycolysis
Describe fast twitch muscle fibres
Contract relatively quickly for a short period of time
Have fewer mitochondria
Have a lower blood supply
Major storage fuel is glycogen
What are fast twitch fibres good for?
Short bursts of activity such as weight lifting or sprinting
