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Human Structure & Function > How do cells grow, specialise & die? > Flashcards

How do cells grow, specialise & die? Flashcards

1
Q

What is DNA?

A
  • DNA: deoxyribonucleic acid
  • Genetic information contained in nucleus
  • Contains genetic information for protein formation
  • Approximately 23 000 genes in human genome
  • Genes code for proteins
  • Only 1.5% of DNA is due to genes
  • 98.5% of DNA is non-coding – e.g regulatory sequences, introns, and noncoding DNA – e.g repeat elements
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2
Q

What is the structure of DNA?

A

-Double-stranded (double helix - twisted ladder)
-Sugar-phosphate backbone
-Complementary nitrogenous bases
o adenine – thymine
o guanine - cytosine

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3
Q

What is the organisation of DNA?

A
  • Double strand of DNA – twisted ladder
  • DNA wrapped around proteins called histones.
  • Histones & DNA bundled together – chromatin
  • Chromatin twists around to make chromosomes
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4
Q

What are maternal & paternal chromosomes

A
  • Each somatic human cell has two copies of each chromosome – one you inherited from Mum and one from Dad.
  • The maternal and paternal chromosomes of a pair are called homologous chromosomes (make a “homologous pair)
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5
Q

How many pairs of autosomal & sex chromosomes do humans have?

A

-Humans have 22 pairs of autosomal chromosomes and 1 pair of sex chromosomes
o Women have 2 X chromosomes and men have an X and Y

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6
Q

In somatic cells & gametes how many chromosomes are there? What happens when cells are dividing?

A
  • Somatic cells with 46 chromosomes (23 pairs) are said to be diploid (have the full amount of DNA)
  • Gametes (sperm and egg) only have 1 chromosome of each homologous pair (have 23 chromosomes) and are called haploid (have half the normal amount of DNA)
  • When cells are dividing, the chromosomes become easier to see and we can arrange them next to their pair – this kind of map is a karyotype
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7
Q

What is a Karyotype?

A

A map of chromosomes in dividing cell

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8
Q

Define genetics, gene, allele, genotype & phenotype

A 
Genetics - study of heredity 
Gene – piece of DNA that codes for a protein 
Allele – alternative form of a gene 
Genotype – the actual gene (allele)
Phenotype - person’s appearance
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9
Q

What are cells?

A
  • Cells are protein factories that constantly synthesize many different proteins
  • These proteins are used for cell functions or can be exported
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10
Q

What do cells DNA contain?

A
  • The cell’s DNA contains all the instructions the cell needs for making proteins
  • Not all cells make all proteins – some proteins are needed only by specific cells.
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11
Q

What is the proteome of a cell?

A
  • The “proteome” of a cell is all the proteins that a cell makes, and “proteomics” is the study of the proteins in a cell.
  • The proteome of one cell can be compared to another to see how they are different.
  • A muscle cell vs a skin cell
  • A melanoma vs a normal melanocyte
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12
Q

What is transcription and translation?

A
  • Transcription= DNA > RNA
  • Translation= RNA > protein
  • Flow of information from DNA to RNA to protein: The Central Dogma
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13
Q

What is transcription?

A
  • DNA has two strands, but only one strand of the DNA is used as a template to make RNA
  • Genetic information (a gene) is copied from a strand of DNA to make a strand of ribonucleic acid (RNA) called mRNA (messenger RNA)
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14
Q

RNA is like DNA except?

A 
-RNA is like DNA except – 
o	Sugar: ribose instead of deoxyribose
o	It is single-stranded 
o	Contains uracil instead of thymine 
-RNA acts as an intermediary between DNA and protein
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15
Q

What is initiated by transcription & mRNA produced is called what?

A
  • Initiated by transcription factors that recruit RNA polymerase enzyme
  • The mRNA produced is called an RNA transcript
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16
Q

What starts and stops a gene?

A

-There are special sequences/signals in DNA that indicate when a gene starts and stops

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17
Q

What is within a gene & what does the initial mRNA transcript contain?

A
  • Within a gene there are exons (coding) and introns (non-coding)
  • The initial mRNA transcript (pre-mRNA) contains both the exons and introns. The RNA introns are then cut out and the exons are all joined together. This transcript is called processed RNA
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18
Q

Name & describe the kinds of RNA transcribed from DNA

A

-Three kinds of RNA are transcribed from DNA
o Messenger RNA (mRNA): is translated in the cytoplasm to make proteins
o Ribosomal RNA (rRNA): together with ribosomal proteins rRNA makes up the ribosomes
o Transfer RNA (tRNA): each tRNA can bind specifically to one of the 20 different amino acids used to build proteins, important in translating mRNA into amino acid peptide

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19
Q

Describe the events that occur when the DNA strands seperate

A

-The strands of DNA are separated
-RNA polymerase binds at a promoter region
-RNA polymerase catalyses the formation of a mRNA chain using the DNA as a template and following the rules of complimentary base pairing
o A with U
o C with G

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20
Q

How does transcription end?

A
  • Transcription ends at a terminator sequence
  • DNA uncoils and unzips
  • RNA polymerase –> messenger RNA (mRNA)
  • mRNA exits nucleus through nuclear pores
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21
Q

What does translation do & where does it occur?

A

-Turns mRNA into a protein
-Occurs in the cytoplasm – by ribosomes
o On rough endoplasmic reticulum (RER)
o Free within cytoplasm

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22
Q

What does mRNA carry?

A

-mRNA carries genetic information from the nucleus to the ribosomes

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23
Q

In translation what is the sequence read by?

A

-The sequence is “read” by translational machinery in the ribosome, in lots of three nucleotides (nucleotide triplets = codon)

24
Q

What does translation start at?

A

-Translation starts at the start codon (AUG) of each gene in the mRNA

25
Q

What does each codon code for & as they’re read what happens?

A
  • Each codon codes for a specific amino acid

- As each codon is read, a tRNA with a complimentary sequence (anticodon) binds to each triplet

26
Q

What does tRNA carry & what are amino acids joined together by?

A
  • The tRNA also carries the amino acid specified by the codon
  • Amino acids are joined together by peptide bonds, in the sequence specified by the mRNA, to make a peptide/protein
27
Q

How many possible codons are there and how many naturally occurring amino acids are there?

A

-There are 64 possible codons in mRNA and only 20 naturally occurring amino acids (aa’s)

28
Q

What do three codons signal?

A

-Three codons do not code for an amino acid but signal termination of the peptide chain – stop codons

29
Q

What is post-translational modification?

A
  • The chemical modification of a protein following translation
  • It is one of the last steps in protein synthesis
30
Q

What can happen after translation?

A

-After translation, proteins can be modified by attaching other functional groups which can change or extend its functions

31
Q

Can amino acids be cleaved off the end of a protein & what do modifications do to the behaviour of proteins?

A
  • Amino acids may be cleaved off the end of the protein or the polypeptide can be cut in half, e.g. insulin
  • Other modifications, such as phosphorylation are a common way of controlling the behaviour of a protein, for instance activating or inactivating an enzyme
32
Q

What is a protein?

A
  • A protein molecule is a long chain of amino acids, each linked to its neighbour by a peptide bond
  • There are many thousands of proteins, each has a unique sequence of amino acids
33
Q

What does each amino acid have as a property?

A

-Each amino acid has specific properties due to its side chains (part of the amino acid not involved in linking to each other)

34
Q

What can some side chains be compared to others?

A

-Some of the side chains are non-polar and hydrophobic (water fearing), others are hydrophilic (water loving), or positively or negatively charged

35
Q

What can affect the way a protein folds & shapes and how many amino acids can a peptide, polypeptide and a protein have?

A

-In a long chain of amino acids, interactions between these side groups, as well as the peptide bonds, affect the way a protein can fold and what shape it is
o Peptide - 2 or more aa’s
o Polypeptide- 10 or more aa’s
o Protein - 50 or more aa’s

36
Q

Describe a primary and secondary protein

A

Primary
-Sequence of amino acids linked by peptide bonds
Secondary
-Proteins folds to form secondary structures because the amino acids have different side chains
-Two regular folding patterns are seen: alpha helices (a keratin) and beta pleated sheets (fibroin, silk)

37
Q

Describe a tertiary and quaternary protein

A

Tertiary
-The 3D shape is determined by the folding of the secondary structure. The a-helices and b-sheets fold to form unique structures which are held together by bonds between amino acids that may be far apart in the actual polypeptide chain
Quaternary
-Combined three-dimensional structure of two or more polypeptide chains.
-E.g. haemoglobin, which consists of 2 alpha and 2 beta chains

38
Q

What is related to its function in a protein and what can proteins be classified as based on their shape/appearance?

A
  • The 3D structure of a protein is related to its function

- Proteins can be classified according to overall shape and appearance as either fibrous or globular

39
Q

Describe what a globular protein is

A

-Polypeptide chain folds up into a compact shape, like a ball with a rough surface
-Usually water soluble
-Mobile
-Chemically active
-Play crucial roles in nearly all biological processes
o e.g. haemoglobin, most enzymes

40
Q

Describe what a fibrous protein is

A

-Simple, elongated 3D structures
-Are insoluble in water and stable
-Provide mechanical support and tensile strength
-Are abundant outside the cell where they make up a lot of the matrix in between cells
o e.g. collagen, keratin, elastin

41
Q

Describe a somatic cell

A

Somatic cell:

  • A biological cell forming the body of a multicellular organism.
  • Most cells.
  • 46 chromosomes (diploid number).
  • Mitosis.
42
Q

Describe a germ cell

A

Germ cell:

  • Cells that give rise to gametes.
  • Located in ovaries and testes
  • Meiosis.
43
Q

Describe a gamete

A

Gamete:

  • Cells that fuse during sexual reproduction.
  • Sperm or egg (oocyte).
  • 23 chromosomes (haploid number).
44
Q

What is interphase?

A

-Cells spend the majority of their life in interphase.
-Interphase: phase between cell divisions
o Replication of DNA
o Ongoing normal cell activities

45
Q

What is mitosis, what are the stages in mitosis & what is cytokinesis?

A 
-Mitosis: series of events that leads to the production of two cells by division of a mother cell into two daughter cells. Cells are genetically identical. 
o	Prophase 
o	Metaphase 
o	Anaphase 
o	Telophase 
-Cytokinesis: division of cell cytoplasm
46
Q

How many centrioles are there and where are they located and before cell division what happens to centrioles?

A
  • 2 centrioles, located in centrosome
  • Centre of microtubule (spindle fibre) formation
  • Before cell division, centrioles divide, move to ends of cell and organize spindle fibres
47
Q

What is a chromatin and what happens to it during cell division?

A
  • Chromatin: DNA complexed with proteins (histones)
  • During cell division, chromatin condenses into pairs of chromatids called chromosomes. Each pair of chromatids is joined by a centromere
48
Q

How many pairs of chromosomes, autonomic, diploid & sex determining are there?

A 
Chromosomes
Humans: 
o	23 pairs of chromosomes
o	46 – Diploid number 
o	22 autonomic pairs 
o	1 sex determining pair. 
XX – female 
XY - male
49
Q

What is homologous, locus & allele?

A
  • Homologous: pairs of chromosomes - where one is from the father and the other is from the mother
  • Locus: the location of a gene on a chromosome
  • Allele: different forms of the same gene
50
Q

What occurs in interphase?

A

Interphase – DNA replication occurs. Each chromosome becomes doubled, consisting of 2 identical strands of DNA.

51
Q

How man cells are produced in mitosis?

A

2 identical daughter cells.

52
Q

Describe what happens in prophase, metaphase, anaphase, telophase & cytokinesis

A

Prophase – chromatin condenses to form chromosomes, centrioles migrate to ends of each cell, spindle fibres attach to centromeres, nuclear envelope disintegrates.
Metaphase – chromosomes are aligned at the nuclear equator
Anaphase – spindle fibres separate the chromatids, 2 identical sets of chromosomes are moved to separate ends of the cell, cytokinesis begins.
Telophase – nuclear envelope reforms around each set of chromosomes, chromosomes decondense into chromatin, cytokinesis continues.
-Cytokinesis – cytoplasmic division.

53
Q

What is meiosis, what is it specialised for, what is produced & what does it result in?

A

-Germ cells divide and produce gametes.
-Specialized for sexual reproduction
-DNA replication followed by two cell divisions
-Produces 4 genetically different daughter cells
o Gametes, haploid (n)
o Only one homolog from each homologous pair
-Resulting gametes (egg, sperm) unite to form a zygote – a new ‘genetically unique’ human being.

54
Q

What happens in prophase 1?

A

-Prophase 1: Homologous chromosomes line up next to each other.

55
Q

What happens in homologous crossing over and what does it result in?

A

-DNA is exchanged between the adjacent homologous chromatids.
-Sister chromatid strands of each chromosome are no longer identical.
-Results in exchange of genetic material between maternal and paternal chromosomes.
o New gene combinations
o Human variation.

Human Structure & Function (11 decks)

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